I think the minimum for simplex communication are TX so we can transmit and the power supply pins +Vcc and GND. That is all we need. When do we need to use all 9 pins of RS-232? I think that the reciever can decipher when data has started coming in and if it knows the baud rate already, it also knows when the latch the incoming bits. Therefore, I don't see the purpose of all the remaining pins on the RS-232 cable besides TX, RX, +Vcc and GND.
Do we still need them? The problem is that I wish to connect a PC to a waveform generator through RS-232 cable. I have the software for this installed on the PC but no RS-232 cable. If I do make my own using RS-232 connectors (which is what I intend) with my own wires soldered to it, how do I know if I just need TX, RX, +Vcc and GND or if I need all the other pins as well?
Soldering all the pins is not such a hard thing to do anyway, but I am just curious. The RS-232 standard was originally specified to support connections between Data Terminal Equipment (DTE) such as computers, teletypes and video display terminals and Data Communications Equipment (DCE) such as modems and Automatic Calling Units (ACUs). At the time, DCE did not have any internal intelligence, so dedicated signals were designed into the RS-232 specification to manage specific features that were common to such equipment, such as flow control, on-hook/off-hook status and call progress. Nowadays, modems have their own microprocessors, so it's actually easier (and cheaper) to ignore the dedicated signals in the RS-232 connector and do everything over the serial data lines, using the ubiquitous 'AT' protocol. The RS-232 (DB9) pinout specifies only the TX and RX pins necessary for communication. The rest of the pins are necessary only if you implement some form of hardware flow control.
In no particular order these are RTS (Request to Send), CTS (Clear to Send), DTR (Data Terminal Ready) and couple others. You can get the details. If your intended hardware doesn't use any form of hardware handshaking (most trivial applications don't; you'd need to check yours, however) you can get away with using the two data pins along with GND.
RS232 serial spy monitor cable. Introduction on monitoring serial RS232 data The RS232 standard defines an asynchronous way of communication between DTE, data terminal equipment (computers, printers, etc.) and DCE, data communication equipment (modems). This type of communication has become the minority and nowadays serial communications is mainly between two DTE devices using a. Although this is 1:1 communication, it is possible with special cables to monitor the data streams. RS232 provides 2 data lines for each data channel. One is for transmitting data and the other for receiving.
Because of these two separate lines, data can be send full duplex. This means that both ends can send and receive data simultaneously without mutual interference.
In most situations however the high level communication protocol only allows half duplex communications because most simple protocols with external devices work with a master-slave, or question-answer configuration. One of the parties is the master which is in charge of communications. This master sends commands and requests to the slave which responds to them. The slave will never by itself start a communication sequence so in practise the communication is half duplex: There is no single moment when both sides send data simultaneously. That most RS232 communication is performed in a half duplex way is important if the data stream has to be monitored. A half duplex communication protocol can be spied with a computer with just one serial port attached. This port listens to both RS232 communication lines simultaneously but no data will be garbled because only one party sends at a time.
This type of communication can be spied with simple software like the terminal emulation program HyperTerminal which is shipped with the Windows operating system. In the situation of full duplex communication on a RS232 channel we cannot simply tie both lines together and listen to it. For this situation you need two separate serial ports on the spionage computer. Also special sniffer software is handy that listens to both ports simultaneously and outputs the data of both lines to the screen or to disk. Half duplex RS232 spy / monitor / sniffer cable It is not difficult to monitor half duplex RS232 serial communication between two devices with a PC.
To do this you need the RS232 monitor cable which is displayed in the next picture. Two DB9 connectors are wired straight through.
The spy computer is connected to the third connector. This monitor cable taps communication from two sources on only one RS232 receiver port.
This means that if the two devices happen to talk simultaneously, the monitored information will be garbage. In most circumstances communication protocols work half duplex, in which case this RS232 cable will work without problems. Otherwise you need the full duplex RS232 monitor cable which is discussed here also.
Half duplex RS232 spy / monitor / sniffer cable Connector 1 Connector 2 Spy Function 1 1 - Carrier detect 2 2 2 via R 1 Rx Rx spy 3 3 2 via D 1 Tx Rx spy 4 4 - Data terminal ready 5 5 5 Signal ground 6 6 - Data set ready 7 7 - Request to send 8 8 - Clear to send 9 9 - Ring indicator -1 + 4 + 6 DTR CD + DSR -7 + 8 RTS CTS The electronic diagram looks simple and strange at the same time with one diode and one resistor. The functionality is however straight forward. The spy computer is attached to the connector in the right bottom.
The female connector at the left is attached to the spied computer and the male connector at the right to the attached device. When an RS232 port is in an, it will be in the so-called marking state with a negative voltage at the transmit output. Assume the computer connected to the left port is sending data and the peripheral device at the right side is idle. At that moment the RS232 signal level on line 3 will change. When the voltage of this line changes to a higher value, current will flow through the diode to the spy computer. We assume the attached device is in an idle state.
Therefore, the voltage at line 2 is something like -12 Volt, while at the other end of the resistor +12 Volt is applied. Simple mathematics learns that a current of approximately 11 mA (=24 Volt/2200 Ohm) flows through the resistor. This is no problem because most RS232 driver IC's are capable to deliver at least 45 mA. Because the voltage drop over the diode is only 0.7 Volt—independent of the current through the diode—the spy computer will see on its RS232 port (almost) the same voltage levels as present on the transmit port of the sending computer and data from the sending computer to the peripheral device is successfully captured.
In the second situation the computer has finished sending data and waits for an answer from the device at the male connector. The RS232 signal level at line 2 will go to positive values. The diode will block current to line 3 so the spy computer effectively only sees the data coming from the peripheral device. Now the spy computer will be able to pick-up the data send from the device back to the computer. In the diagram for the half duplex monitor cable some shorts have been made between pins of the connector of the spying computer. These shorts loopback the handshaking signals of the computer.
In most cases these shorts won't be necessary, but if the spy monitoring software uses handshaking, this will prevent the monitor software from blocking. You don't need expensive software to use this RS232 spy cable. A simple serial terminal emulator like the HyperTerminal program present on all Windows based computers is enough to spy your communications. The only thing you need to do is changing the baudrate and start and stop bits settings from the terminal emulation program to the settings used on the line to monitor.
Full duplex RS232 spy / monitor / sniffer cable As already discussed, it is not possible to monitor a full duplex RS232 communication with only one spy port. For this purpose the full duplex monitor cable can be used.
This cable connects to two serial ports on the spy computer where each ports taps one direction of the communication. You could open two sessions of a terminal emulation program on your computer, but often better is to use one of the specialized RS232 monitor software products. In that way the two communication streams are merged in one screen which makes it easier to analyze the sequence of the communications. Full duplex RS232 spy / monitor / sniffer cable Connector 1 Connector 2 Spy port 1 Spy port 2 Description 1 1 -Carrier detect 2 2 2 - Rx Rx 1 3 3 - 2 Tx Rx 2 4 4 -Data terminal ready 5 5 5 5 Signal ground 6 6 -Data set ready 7 7 -Request to send 8 8 -Clear to send 9 9 -Ring indicator -1 + 4 + 6 - DTR CD + DSR -7 + 8 - RTS CTS -1 + 4 + 6 DTR CD + DSR -7 + 8 RTS CTS The diagram of the full duplex RS232 monitor cable is actually simpler than the diagram of the half duplex monitor cable. This is because no special circuitry is necessary to combine two communication lines on one input. Just to be sure, all handshake signals on both spy connectors have been looped back. This prevents the software from blocking input in case it checks the CTS, DSR or CD inputs.
Other RS232 monitor solutions Besides the cables mentioned above, there are ready made adapters available on the market which monitor serial communications on RS232 channels. An interesting product is the from Stratus Engineering. It allows you to monitor RS232 communications via the USB port.
A connector as described in the RS-232 standard In, RS-232, 232 is a introduced in 1960 for transmission of data. It formally defines the signals connecting between a DTE ( ) such as a, and a DCE ( or ), such as a. The RS-232 standard had been commonly used in. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and of connectors. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997. An RS-232 serial port was once a standard feature of a, used for connections to, data storage, and other peripheral devices.
RS-232, when compared to later interfaces such as, and, has lower transmission speed, short maximum cable length, large voltage swing, large standard connectors, no multipoint capability and limited multidrop capability. In modern personal computers, has displaced RS-232 from most of its peripheral interface roles. Many computers no longer come equipped with RS-232 ports (although some come equipped with a COM port header that allows the user to install a bracket with a DE-9 port) and must use either an external USB-to-RS-232 converter or an internal expansion card with one or more serial ports to connect to RS-232 peripherals. Nevertheless, thanks to their simplicity and past ubiquity, RS-232 interfaces are still used—particularly in industrial machines, networking equipment, and scientific instruments where a short-range, point-to-point, low-speed wired data connection is adequate. Contents. Scope of the standard The (EIA) standard RS-232-C as of 1969 defines:. Electrical signal characteristics such as voltage levels, timing, and of signals, voltage withstand level, behavior, and maximum load.
Interface mechanical characteristics, pluggable connectors and pin identification. Functions of each circuit in the interface connector. Standard subsets of interface circuits for selected telecom applications. The standard does not define such elements as the (i.e., or others), the framing of characters (start or stop bits, etc.), transmission order of bits, or error detection protocols.
The character format and transmission bit rate are set by the serial port hardware which may also contain circuits to convert the internal to RS-232 compatible signal levels. The standard does not define bit rates for transmission, except that it says it is intended for lower than 20,000 bits per second. History RS-232 was first introduced in 1960 by the (EIA) as a Recommended Standard. The original DTEs were electromechanical, and the original DCEs were (usually) modems. When (smart and dumb) began to be used, they were often designed to be interchangeable with teletypewriters, and so supported RS-232. The C revision of the standard was issued in 1969 in part to accommodate the electrical characteristics of these devices. Because the standard did not foresee the requirements of devices such as computers, printers, test instruments, and so on, designers implementing an RS-232 compatible interface on their equipment often interpreted the standard idiosyncratically.
The resulting common problems were non-standard pin assignment of circuits on connectors, and incorrect or missing control signals. The lack of adherence to the standards produced a thriving industry of, patch boxes, test equipment, books, and other aids for the connection of disparate equipment. A common deviation from the standard was to drive the signals at a reduced voltage. Some manufacturers therefore built transmitters that supplied +5 V and −5 V and labeled them as 'RS-232 compatible'. Later personal computers (and other devices) started to make use of the standard so that they could connect to existing equipment. For many years, an RS-232-compatible port was a standard feature for, such as modem connections, on many computers (with the computer acting as the DTE). It remained in widespread use into the late 1990s.
In personal computer peripherals, it has largely been supplanted by other interface standards, such as USB. RS-232 is still used to connect older designs of peripherals, industrial equipment (such as ), ports, and special purpose equipment. The standard has been renamed several times during its history as the sponsoring organization changed its name, and has been variously known as EIA RS-232, EIA 232, and, most recently as TIA 232. The standard continued to be revised and updated by the and since 1988 by the (TIA). Revision C was issued in a document dated August 1969. Revision D was issued in 1986. The current revision is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997.
Changes since Revision C have been in timing and details intended to improve harmonization with the standard V.24, but equipment built to the current standard will interoperate with older versions. Related standards include V.24 (circuit identification) and V.28 (signal voltage and timing characteristics). In revision D of EIA-232, the D-subminiature connector was formally included as part of the standard (it was only referenced in the appendix of RS-232-C).
The voltage range was extended to ±25 volts, and the circuit capacitance limit was expressly stated as 2500 pF. Revision E of EIA-232 introduced a new, smaller, standard D-shell 26-pin 'Alt A' connector, and made other changes to improve compatibility with CCITT standards V.24, V.28 and ISO 2110. Main article: In the book Hardware Design Guide, deprecated support for the RS-232 compatible serial port of the original IBM PC design. Today, RS-232 has mostly been replaced in personal computers by for local communications. Advantages compared to RS-232 are that USB is faster, uses lower voltages, and has connectors that are simpler to connect and use. Disadvantages of USB compared to RS-232 are that USB is far less immune to (EMI) – and that maximum cable length is much shorter (15 meters for RS-232 v.s.
3 - 5 meters for USB depending on USB speed used). In fields such as laboratory automation or surveying, RS-232 devices may continue to be used. Some types of, and equipment are programmable via RS-232.
Computer manufacturers have responded to this demand by re-introducing the connector on their computers or by making adapters available. RS-232 ports are also commonly used to communicate to such as, where no monitor or keyboard is installed, during boot when is not running yet and therefore no network connection is possible. A computer with an RS-232 serial port can communicate with the serial port of an (such as a ) as an alternative to monitoring over Ethernet.
Physical interface In RS-232, user data is sent as a of. Both synchronous and asynchronous transmissions are supported by the standard. In addition to the data circuits, the standard defines a number of control circuits used to manage the connection between the DTE and DCE. Each data or control circuit only operates in one direction, that is, signaling from a DTE to the attached DCE or the reverse. Because transmit data and receive data are separate circuits, the interface can operate in a manner, supporting concurrent data flow in both directions. The standard does not define character framing within the data stream, or character encoding. Voltage levels.
RS-232 data line on the terminals of the receiver side (RxD) probed by an oscilloscope (for an ASCII 'K' character (0x4B) with 1 start bit, 8 data bits, 1 stop bit, and no parity bits). The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for the data transmission and the control signal lines. Valid signals are either in the range of +3 to +15 volts or the range −3 to −15 volts with respect to the 'Common Ground' (GND) pin; consequently, the range between −3 to +3 volts is not a valid RS-232 level. For data transmission lines (TxD, RxD, and their secondary channel equivalents), logic one is defined as a negative voltage, the signal condition is called 'mark'. Logic zero is positive and the signal condition is termed 'space'. Control signals have the opposite polarity: the asserted or active state is positive voltage and the deasserted or inactive state is negative voltage. Examples of control lines include request to send (RTS), clear to send (CTS), (DTR), and data set ready (DSR).
RS-232 logic and voltage levels Data circuits Control circuits Voltage 0 (space) Asserted +3 to +15 V 1 (mark) Deasserted −15 to −3 V The standard specifies a maximum open-circuit voltage of 25 volts: signal levels of ±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the voltages available to the line driver circuit. Some RS-232 driver chips have inbuilt circuitry to produce the required voltages from a 3 or 5 volt supply. RS-232 drivers and receivers must be able to withstand indefinite short circuit to ground or to any voltage level up to ±25 volts.
The, or how fast the signal changes between levels, is also controlled. Because the voltage levels are higher than logic levels typically used by integrated circuits, special intervening driver circuits are required to translate logic levels. These also protect the device's internal circuitry from short circuits or transients that may appear on the RS-232 interface, and provide sufficient current to comply with the slew rate requirements for data transmission. Because both ends of the RS-232 circuit depend on the ground pin being zero volts, problems will occur when connecting machinery and computers where the voltage between the ground pin on one end, and the ground pin on the other is not zero.
This may also cause a hazardous. Use of a common ground limits RS-232 to applications with relatively short cables. If the two devices are far enough apart or on separate power systems, the local ground connections at either end of the cable will have differing voltages; this difference will reduce the noise margin of the signals.
Balanced, differential serial connections such as, and USB can tolerate larger ground voltage differences because of the differential signaling. Unused interface signals terminated to ground will have an undefined logic state. Where it is necessary to permanently set a control signal to a defined state, it must be connected to a voltage source that asserts the logic 1 or logic 0 level, for example with a pullup resistor. Some devices provide test voltages on their interface connectors for this purpose. Connectors RS-232 devices may be classified as Data Terminal Equipment (DTE) or Data Circuit-terminating Equipment (DCE); this defines at each device which wires will be sending and receiving each signal.
According to the standard, male connectors have DTE pin functions, and female connectors have DCE pin functions. Other devices may have any combination of connector gender and pin definitions. Many terminals were manufactured with female connectors but were sold with a cable with male connectors at each end; the terminal with its cable satisfied the recommendations in the standard. The standard recommends the 25-pin connector up to revision C, and makes it mandatory as of revision D. Most devices only implement a few of the twenty signals specified in the standard, so connectors and cables with fewer pins are sufficient for most connections, more compact, and less expensive. Personal computer manufacturers replaced the connector with the smaller connector. This connector, with a different pinout (see ), is prevalent for personal computers and associated devices.
Presence of a 25-pin D-sub connector does not necessarily indicate an RS-232-C compliant interface. For example, on the original IBM PC, a male D-sub was an RS-232-C DTE port (with a non-standard interface on reserved pins), but the female D-sub connector on the same PC model was used for the.
Some personal computers put non-standard voltages or signals on some pins of their serial ports. Main article: The standard does not define a maximum cable length, but instead defines the maximum capacitance that a compliant drive circuit must tolerate. A widely used rule of thumb indicates that cables more than 15 m (50 ft) long will have too much capacitance, unless special cables are used. By using low-capacitance cables, communication can be maintained over larger distances up to about 300 m (1,000 ft). For longer distances, other signal standards are better suited to maintain high speed. Since the standard definitions are not always correctly applied, it is often necessary to consult documentation, test connections with a, or use trial and error to find a cable that works when interconnecting two devices. Connecting a fully standard-compliant DCE device and DTE device would use a cable that connects identical pin numbers in each connector (a so-called 'straight cable').
' are available to solve gender mismatches between cables and connectors. Connecting devices with different types of connectors requires a cable that connects the corresponding pins according to the table below.
Cables with 9 pins on one end and 25 on the other are common. Manufacturers of equipment with connectors usually provide a cable with either a DB-25 or DE-9 connector (or sometimes interchangeable connectors so they can work with multiple devices). Poor-quality cables can cause false signals by between data and control lines (such as ).
If a given cable will not allow a data connection, especially if a is in use, a cable may be necessary. Gender changers and null modem cables are not mentioned in the standard, so there is no officially sanctioned design for them. 3-wire and 5-wire RS-232 A minimal '3-wire' RS-232 connection consisting only of transmit data, receive data, and ground, is commonly used when the full facilities of RS-232 are not required. Even a two-wire connection (data and ground) can be used if the data flow is one way (for example, a digital postal scale that periodically sends a weight reading, or a GPS receiver that periodically sends position, if no configuration via RS-232 is necessary).
When only hardware flow control is required in addition to two-way data, the RTS and CTS lines are added in a 5-wire version. Data and control signals The following table lists commonly used RS-232 signals (called 'circuits' in the specifications) and their pin assignments on the recommended DB-25 connectors. (See ) for other commonly used connectors not defined by the standard.) Circuit Direction pin Name Typical purpose Abbreviation DTE DCE DTE is ready to receive, initiate, or continue a call. DTR out in 20 DCE is receiving a carrier from a remote DCE. DCD in out 8 Data Set Ready DCE is ready to receive and send data.
DSR in out 6 Ring Indicator DCE has detected an incoming ring signal on the telephone line. RI in out 22 Request To Send DTE requests the DCE prepare to transmit data. RTS out in 4 Ready To Receive DTE is ready to receive data from DCE. If in use, RTS is assumed to be always asserted. RTR out in 4 Clear To Send DCE is ready to accept data from the DTE. CTS in out 5 Transmitted Data Carries data from DTE to DCE. TxD out in 2 Received Data Carries data from DCE to DTE.
RxD in out 3 Common Ground Zero voltage reference for all of the above. GND common 7 Protective Ground Connected to chassis ground.
PG common 1 The signals are named from the standpoint of the DTE. For the other connections, and establishes the 'zero' voltage to which voltages on the other pins are referenced. The DB-25 connector includes a second 'protective ground' on pin 1; this is connected internally to equipment frame ground, and should not be connected in the cable or connector to signal ground. Ring Indicator Ring Indicator (RI) is a signal sent from the DCE to the DTE device.
It indicates to the terminal device that the phone line is ringing. In many computer serial ports, a is generated when the RI signal changes state. Having support for this hardware interrupt means that a program or operating system can be informed of a change in state of the RI pin, without requiring the software to constantly 'poll' the state of the pin.
RI does not correspond to another signal that carries similar information the opposite way. On an external modem the status of the Ring Indicator pin is often coupled to the 'AA' (auto answer) light, which flashes if the RI signal has detected a ring. The asserted RI signal follows the ringing pattern closely, which can permit software to detect patterns. The Ring Indicator signal is used by some older (UPSs) to signal a power failure state to the computer.
Certain personal computers can be configured for, allowing a computer that is suspended to answer a phone call. RTS, CTS, and RTR.
Further information: The RTS and CTS signals were originally defined for use with half-duplex (one direction at a time) modems such as the. These modems disable their transmitters when not required and must transmit a synchronization preamble to the receiver when they are re-enabled. The DTE asserts RTS to indicate a desire to transmit to the DCE, and in response the DCE asserts CTS to grant permission, once synchronization with the DCE at the far end is achieved. Such modems are no longer in common use. There is no corresponding signal that the DTE could use to temporarily halt incoming data from the DCE. Thus RS-232's use of the RTS and CTS signals, per the older versions of the standard, is asymmetric. This scheme is also employed in present-day RS-232 to converters.
RS-485 is a multiple-access bus on which only one device can transmit at a time, a concept that is not provided for in RS-232. The RS-232 device asserts RTS to tell the converter to take control of the RS-485 bus so that the converter, and thus the RS-232 device, can send data onto the bus. Modern communications environments use full-duplex (both directions simultaneously) modems. In that environment, DTEs have no reason to deassert RTS. However, due to the possibility of changing line quality, delays in processing of data, etc., there is a need for symmetric, bidirectional. A symmetric alternative providing flow control in both directions was developed and marketed in the late 1980s by various equipment manufacturers. It redefined the RTS signal to mean that the DTE is ready to receive data from the DCE.
This scheme was eventually codified in version RS-232-E (actually TIA-232-E by that time) by defining a new signal, 'RTR (Ready to Receive)', which is CCITT V.24 circuit 133. TIA-232-E and the corresponding international standards were updated to show that circuit 133, when implemented, shares the same pin as RTS (Request to Send), and that when 133 is in use, RTS is assumed by the DCE to be asserted at all times. In this scheme, commonly called 'RTS/CTS flow control' or 'RTS/CTS handshaking' (though the technically correct name would be 'RTR/CTS'), the DTE asserts RTR whenever it is ready to receive data from the DCE, and the DCE asserts CTS whenever it is ready to receive data from the DTE. Unlike the original use of RTS and CTS with half-duplex modems, these two signals operate independently from one another. This is an example of.
However, 'hardware flow control' in the description of the options available on an RS-232-equipped device does not always mean RTS/CTS handshaking. Equipment using this protocol must be prepared to buffer some extra data, since the remote system may have begun transmitting just before the local system deasserts RTR.
Seldom-used features The EIA-232 standard specifies connections for several features that are not used in most implementations. Their use requires 25-pin connectors and cables. Signal rate selection The DTE or DCE can specify use of a 'high' or 'low' signaling rate. The rates, as well as which device will select the rate, must be configured in both the DTE and DCE. The prearranged device selects the high rate by setting pin 23 to ON. Loopback testing Many DCE devices have a capability used for testing. When enabled, signals are echoed back to the sender rather than being sent on to the receiver.
If supported, the DTE can signal the local DCE (the one it is connected to) to enter loopback mode by setting pin 18 to ON, or the remote DCE (the one the local DCE is connected to) to enter loopback mode by setting pin 21 to ON. The latter tests the communications link, as well as both DCEs. When the DCE is in test mode, it signals the DTE by setting pin 25 to ON. A commonly used version of loopback testing does not involve any special capability of either end. A hardware loopback is simply a wire connecting complementary pins together in the same connector (see ). Loopback testing is often performed with a specialized DTE called a (or BERT). Timing signals Some synchronous devices provide a to synchronize data transmission, especially at higher data rates.
Two timing signals are provided by the DCE on pins 15 and 17. Pin 15 is the transmitter clock, or send timing (ST); the DTE puts the next bit on the data line (pin 2) when this clock transitions from OFF to ON (so it is stable during the ON to OFF transition when the DCE registers the bit). Pin 17 is the receiver clock, or receive timing (RT); the DTE reads the next bit from the data line (pin 3) when this clock transitions from ON to OFF. Alternatively, the DTE can provide a clock signal, called transmitter timing (TT), on pin 24 for transmitted data.
Data is changed when the clock transitions from OFF to ON, and read during the ON to OFF transition. TT can be used to overcome the issue where ST must traverse a cable of unknown length and delay, clock a bit out of the DTE after another unknown delay, and return it to the DCE over the same unknown cable delay. Since the relation between the transmitted bit and TT can be fixed in the DTE design, and since both signals traverse the same cable length, using TT eliminates the issue. TT may be generated by looping ST back with an appropriate phase change to align it with the transmitted data.
ST loop back to TT lets the DTE use the DCE as the frequency reference, and correct the clock to data timing. Synchronous clocking is required for such protocols as, and. Secondary channel A secondary data channel, identical in capability to the primary channel, can optionally be implemented by the DTE and DCE devices. Pin assignments are as follows: Signal Pin Common Ground 7 (same as primary) Secondary Transmitted Data (STD) 14 Secondary Received Data (SRD) 16 Secondary Request To Send (SRTS) 19 Secondary Clear To Send (SCTS) 13 Secondary Carrier Detect (SDCD) 12 Related standards Other serial signaling standards may not interoperate with standard-compliant RS-232 ports. For example, using the of near +5 and 0 V puts the mark level in the undefined area of the standard. Such levels are sometimes used with -compliant receivers and. A 20 mA uses the absence of 20 mA current for high, and the presence of current in the loop for low; this signaling method is often used for long-distance and links.
Connection of a current-loop device to a compliant RS-232 port requires a level translator. Current-loop devices can supply voltages in excess of the withstand voltage limits of a compliant device. The original IBM PC serial port card implemented a 20 mA current-loop interface, which was never emulated by other suppliers of equipment.
. RS232 uses single ended TX and RX. This means a common ground wire is shared between TX and RX. Only 3 wires are needed for a data-only serial channel: TX, RX, and GND. Disadvantages of single ended signaling is that it is more susceptible to noise than differential signaling, effective cable distances are shorter and data rates are slower. The voltage ranges of RS232 signaling is +3V to +15V for a 'high' and -3V to -15V for a 'low'.
RS423 uses single ended TX and differential RX. TX is comprised of 2 wires:.
TX+, a single ended signal, and TX- (which is really just GND). RX is comprised of RX+ and RX-, which go into a true differential receiver. 4 wires are needed for a data-only serial channel: TX+, TX- (GND), RX+ and RX. The single ended TX+ pin drives the RX pin of an RS232 port.
TX- (GND) just ties to the RS232 GND pin and provides a common GND. The voltage levels of signaling is +5V for a 'high' and -5V for a 'low', which is within the RS232 voltage level ranges mentioned above. RS422 uses differential TX and RX. The TX pair of wires TX+ and TX- either drive. TX+ to 5V and TX- to 0V for a 'high', or. TX+ to 0V and TX- to 5V for a 'low'. TX- is not tied to GND as in RS423, instead it drives 'opposite' the voltage that is on the TX+ pin.
RS422 RX+ and RX- detect differential voltages just as in the RS423 case. 4 wires are needed for a data only serial channel: TX+, TX-, RX+ and RX.
Since the TX pair of wires does not have a GND wire, RS422/RS485 can not be connected directly to an RS232 port. Attempting to do this (by connecting RS422 TX+ to RS232 RX and RS422 TX- to RS232 GND) would cause. the RS422 TX- pin to be held at GND and. the RX422 TX+ pin would drive 5V for 'high' (which is valid RS232) and 0V for 'low' (which is not a valid RS232 signal level).
Since RS422/RS485 are truly differential for both TX and RX, cable distances can be much longer and data rates much higher than RS232. If twisted pair cabling is used, (which makes sense because you end up with a complementary TX+ and TX- pair and RX+ and RX- pair), you reduce EMI emissions because the wire pairs help to cancel external transmissions. These wire pairs also reduce the impact of external electrical noise on the signaling. RS485 uses differential TX and RX as in RS422, however RS485 is a superset of RS422. It adds a slightly wider input voltage range on its RX pair, to make it less susceptible to noise and GND potential differences among RS485 devices. RS485 also adds multidrop capability. There can be up to 32 RS485 devices on a single set of serial lines.
This is achieved by having an 'output enable' on the TX ports and allowing only one RS485 device to transmit at a time on a given pair of wires. No isolation transformer is needed as in Appletalk described below. RS485 serial 'networks' can be wired for 2 or 4 wire mode. In 2-wire mode, only one RS485 device can transmit at a time, this is known as half-duplex communication.
An advantage to this topology is that you can save on cabling cost since the cable can be several thousand feet in length. In 4-wire mode, a single RS485 device is designated as the 'master' device.
It's TX pair is connected to all the other 'slave' devices' RX pairs, and all the slave's TX pairs are tied to the master's RX pair. This has the advantage of enabling the master device to transmit to the slaves while a single slave device may also transmit back to the master simultaneously. This is known as full-duplex communication.
Another advantage of this topology is that the slaves are unable to inadvertently transmit to each other's RX pairs because they are not physically connected. This may make it easier to run slaves of different protocols on the same serial network. In 4-wire mode, the Device Server's serial port or screw terminal port can be connected directly to another RS422/RS485 port. The RS485 port cannot be connected directly to an RS232 port without an RS485-to-RS232 adapter for reasons described above in the RS422 section. Since, like RS422, RS485 is differential it has similar cable length, data rate and noise immunity characteristics to RS422 described above.
Appletalk uses a variation of RS422. TX+ and TX- are 'turned off' into a high impedance state (Tristate) where they are not driving a valid differential voltage. By doing this they enable multidrop capabilities where multiple parties can share a common set of serial lines. This is somewhat similar to RS485 described above, however Appletalk typically also includes an isolation transformer between the RS422 driver and the serial cable. There are no Lantronix products that support Appletalk.
Description With this professional 4 port RS232 to USB FTDI chip adapter you can easily add 4 standard serial ports to your desktop, laptop or other mobile device. The Professional 4 Port RS232 USB to Serial outputs are automatically configured as additional COM ports with Windows, Linux, and Mac. This device also offers protection against static electricity, high voltage spikes and other dangerous electrical shocks which can damage your equipment or data signaling. The 4 Port RS232 USB to Serial Adapter is compatible with most GPS and PDA devices such as Garmin, Magellan, and Palm. Office equipment such as modems, printers, scanners, and digital cameras are also compatible.
With protection against static electricity and surges up to 15KV, the Professional 4 Port RS232 USB to Serial converter cable gives you reliable data transfers and protects the converter and your equipment from damage due to over voltages. Package Contents:. 4 Port RS232 USB to Serial Adapter. CD For Drivers (also available for download). GM-FTDI4X Product Manual (also available for download) The USB Plug and Play feature allows easy installation and requires n o configuration for IRQ, DMA, or I/O port resources, meaning more devices can be attached to your system without the hassles of device and resource conflicts.
The converter is suitable for general office, commercial and industrial use. Just like most of our other converters, this adapter is using the high quality FTDI chip which makes it fully compatible with all versions of Windows, Linux, and Mac. OS Support:.
WinXP, 2000, 2003, CE, Vista, 7, 8, 10. Linux. Mac OS 10.X Features & Specifications:. Easy Plug and Play installation.
USB interface: standard Type A female. Automatic handshake support. Baud rates up to 921.600bps. No power supply needed. Dual 16 Byte hardware data buffer (up/down stream).
Parallel Cables
Cable Length 3 feet. Supported in Windows 10. I was using a couple of individual usb-serial converters in my ham shack, and acquired two more pieces of equipment that needed serial ports. I ran across this item and decided to give it a try. I’m glad I did. Installation was a breeze on my Win 7 Pro 32-bit system, and the product functions extremely well, even in a strong RF environment. Each serial connector in the octopus cable is marked (A,B,C,D) and windows assigned Com8,Com9,Com10,Com11 respectively.
These assignments remain across reboots, so there is no reconfiguring of application software. No muss, no fuss. This product uses the latest ultra-reliable FTDI-4232 chipset, and the drivers are Microsoft certified. As the title states, money well spent! This USB to serial port adapter has 4 separate serial cables that connect to a single USB 2.0 plug.
Each of the 4 serial cable ends is slightly more than 3 feet long. The USB cable end is one foot long. Total end-to-end length is a little bit more than 4 feet long. Each serial cable is labeled “1”, “2”, “3”, or “4” which makes it easy to track your connections. The connections always retain the same com port, so you won’t need to reconfigure you software after restarting you computer.
Daedelus music. The adapter has 3 separate LEDs: red = power, green = TX, yellow = RX. The adapter comes with a CD-ROM that contains USB 1.1 and USB 2.0 drivers for many operating systems including Linux, Mac, Windows, and more. The release notes on the CD-ROM mention that newer drivers can be found at No paper instruction manual is included which might cause inexperienced computer users to have moderate difficulty with the setup. Experienced users will find the setup straight forward and simple. Installation on Windows 7 was easy for me. I found the appropriate installer on the CD-ROM.
I had to right-click the installer and select run-as-administrator. The first time I plugged the adapter in it took several minutes for the device to be detected, so be patient. Subsequent detection’s are fast. All 4 serial adapters can be used simultaneously. Overall I am satisfied with the quality of this device.Reviewed at Amazon.com. This USB to serial port adapter has 4 separate serial cables that connect to a single USB 2.0 plug.
Each of the 4 serial cable ends is slightly more than 3 feet long. The USB cable end is one foot long. Total end-to-end length is a little bit more than 4 feet long.
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Each serial cable is labeled “1”, “2”, “3”, or “4” which makes it easy to track your connections. The connections always retain the same com port, so you won’t need to reconfigure you software after restarting you computer. The adapter has 3 separate LEDs: red = power, green = TX, yellow = RX. The adapter comes with a CD-ROM that contains USB 1.1 and USB 2.0 drivers for many operating systems including Linux, Mac, Windows, and more.
The release notes on the CD-ROM mention that newer drivers can be found at No paper instruction manual is included which might cause inexperienced computer users to have moderate difficulty with the setup. Experienced users will find the setup straight forward and simple. Installation on Windows 7 was easy for me. I found the appropriate installer on the CD-ROM.
I had to right-click the installer and select run-as-administrator. The first time I plugged the adapter in it took several minutes for the device to be detected, so be patient. Subsequent detections are fast. All 4 serial adapters can be used simultaneously. Overall I am satisfied with the quality of this device. I purchased this product to help study Cisco as others have already said in previous reviews.
However, everyone else stated they were using the product with a Windows computer. I plugged this quad port USB to serial cable into my Ubuntu server running 12.04 and dmesg shows that it registered immediately. Quickly mapped each of the USB ports to a telnet port and it works perfectly.
The only gripe I have about the product is the studs aren’t female, but I knew that purchasing the product just from looking at the photos. Time to sell the access server that eats up electricity since this has replaced it and doesn’t consume a dime! In short, the GearMo 4-port serial adapter ROCKS! I am a professional network engineer and often need to connect to serial console ports on routers, switches, firewalls and more. An RS232 serial connection is pretty much the industry standard for a local console connection to these devices.
Since it’s common for me to be working on several devices at once — often trying to make coordinated changes on 2 or 4 devices that must be executed with relatively precise timing — this product seemed like a better option than moving my console cable back and forth between devices. The 36″ cables are a bit bulky when coiled up but the spare length for connections is great when working in a data center rack. The FTDI chipset retains its COM port assignment on Windows after reboots and regardless of which USB port the adapter is connected to — an enormous improvement over the PL2303 chipset which always changes its COM port assignment. Each RS232 port is embossed with a number (1-4) that indicates which port it is. I mapped these to COM11-14 on my system so I could make an easy mental association with the COM port to the physical connector. This item also works reliably in Mac and Linux OSes. I’ve been strongly considering building a battery-powered RaspberryPi terminal server with one or two of these to provide an easy-to-access WiFi-connected terminal server.
I guess you get what you pay for, this was more than similar items found on auction sites cheaper. The big difference is this one works! As a ham radio operator we have all lamented the loss of the once ubiquitous serial port.
While there are a bunch of cheap Chinese cables they used cloned chips that may or may not work with drivers and software. I plugged this in, installed the drivers and it assigned 16, 17,18 and 19 as serial ports.
I am running a Navigator interface that uses a number of ports below that. I could have reassigned any of them via the control panel but left them as is. I Have a serial to CT converter for my Icom on 16, a Harris modem on 17, a GPS disciplined Oscillator on 18 and a homebrew antenna patch panel on 19 and they all work with all my various software. HRD, MARS ALE, Comm terminal, 110A both hardware via the Harris and Software.
All USB Connectors
I am no longer tearing my hair out every time a windows update reboots me! What a difference real FTDI chips and non Chinese bootleg drivers makes.
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