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Nolan Garcia
Nolan Garcia

Rs232 Serial Cable Pin Configuration

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 ground loop. 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 RS-422 or RS-485 can tolerate larger ground voltage differences because of the differential signaling.[11]

rs232 serial cable pin configuration


When developing or troubleshooting systems using RS-232, close examination of hardware signals can be important to find problems. This can be done using simple devices with LEDs that indicate the logic levels of data and control signals. "Y" cables may be used to allow using another serial port to monitor all traffic on one direction. A serial line analyzer is a device similar to a logic analyzer but specialized for RS-232's voltage levels, connectors, and, where used, clock signals; it collects, stores, and displays the data and control signals, allowing developers to view them in detail. Some simply display the signals as waveforms; more elaborate versions include the ability to decode characters in ASCII or other common codes and to interpret common protocols used over RS-232 such as SDLC, HDLC, DDCMP, and X.25. Serial line analyzers are available as standalone units, as software and interface cables for general-purpose logic analyzers and oscilloscopes, and as programs that run on common personal computers and devices.

The purpose of a null-modem serial cable is to permit two RS-232 devices to communicate with each other without modems or other communication devices between them. To achieve this, the most obvious connection is that the TxD signal of one device must be connected to the RxD input of the other device (and vice versa).

The following table is a general guide to the cable length base on the baudrate. Please note that this is only a general guide. The material and the construct of the cable also plays a part in the length of the cable. To be safe, it is better to have a margin factor of 2. If you really want to stretch the cable length further, ensure that you get yourself a high quality RS232 cable and also use a better serial data protocol to detect data corruption and do the necessary data re-transmission.

The front panel or serial port can be used for SecureSync configuration or to obtain select data. The serial port is a standard DB9 female port. Communication with this port is via a standard DB9 F to DB9M serial cable (minimum pinout is pin 2 to 2, pin 3 to 3 and pin 5 to 5) connected to a PC running a terminal emulator program such as Tera Term or Microsoft HyperTerminal. The port settings of the terminal emulator should be configured as 9600, N, 8, 1 (flow control setting does not matter).

Using a multimeter, ring out the pins from one end of the serial cable to the other. Verify the cable is pinned as a straight-thru serial cable (pin 2 to 2, pin 3 to 3 and pin 5 to 5) and not as a null-modem or other pin-out configuration.

If you do not plan to use a serial port for accessing another device or for data connection through a modem, you can configure it as a serial console. The first serial port is configured as a serial console, but you can choose to unconfigure it to free it for other applications. A free serial port can also be used to access other routers' (or other equipment, like switches) serial consoles from a MikroTik RouterOS router. A special null-modem cable is needed to connect two hosts (like, two PCs, or two routers; not modems). Note that a terminal emulation program (e.g., HyperTerminal on Windows or minicom on linux) is required to access the serial console from another computer.

Note that the above diagram will not work if the software is configured to do hardware flow control, but the hardware does not support it (e.g., some RouterBOARD models have reduced serial port functionality). If this is the case, either turn off the hardware flow control or use a null-modem cable with loopback, which will simulate the other device's handshake signals with it's own. The diagram for such a cable is as follows:

Plug one end of the serial cable into the console port (also known as a serial port or DB9 RS232C asynchronous serial port) of the RouterBOARD and the other end in your PC (which hopefully runs Windows or Linux). You can also use a USB-Serial adapter. Run a terminal program (HyperTerminal, or Putty on Windows) with the following parameters for All RouterBOARD models except 230:

The serial port to be used as a serial terminal needs to be free (e.g., there should not be any serial consoles, LCD or other configuration). Check the previous chapter to see how to disable serial console on a particular port. Use /port print command to see if some other application is still using the port.

There are two versions of the serial port for the RMC product. The current style is a male DTE DB9. Early production RMCs have a female DTE DB9. However, because both connectors are DTE, the wiring is the same, so only a gender changer is needed to convert a cable between the two ports.

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If you wish to connect your Raspberry Pi to a PC with a USB port, the simplest option is to use a USB-to-serial cable which uses 3.3 V logic levels (e.g. the Adafruit 954 cable, the FTDI TTL-232R-RPI cable, or the Debug Buddy ultimate serial port). These can be simply plugged in directly to the GPIO header (see illustration).

You can connect the Raspberry Pi to a PC using a USB-serial cable, or (if it has an RS-232 port) a level-converter circuit - see above for details. When this is done, you will need to set up a terminal emulator program on your PC as described below.

The easiest way to set up a network connection between your Raspberry Pi and another computer is with an Ethernet cable. If this is not possible, as is the case for the Raspberry Pi Model A, you can set up a connection over the serial cable. This uses the Point-to-point Protocol (PPP). A network connection running over a serial cable can be very useful for copying files onto the Raspberry Pi.

If you are unsure of the COM port, run [Device Manager] and look under 'Ports'. USB-attached serial adapters should have the name of the adapter shown (the Adafruit cable comes up as 'Prolific USB-to_Serial Comm Port'.

The cable is used in conjunction with the Redpark Serial Cable SDK. Together these tools enable hobbyist, education and enterprise developers to write iOS apps that communicate with serial devices. These apps may be deployed for private use at home, at school or in an office. Under current Apple policy this cable may not be used with apps sold on the App Store.

Q: Can I power the iOS device using this cable?A: No. Depending upon which Redpark serial cable you are using, it may be possible to power the iOS device using an accessory named DockStubz. Customers have reported to us that they are using DockStubz from CableJive for this purpose. DockStubz is compatible with our C2-DB9 and C2-TTL cables but is not compatible with our C2-DB9V cable.

Q: Can I power the serial device using this cable?A: Power is not supplied through a RS232 connection. Some very low power devices make use of the RS232 signal lines to supply power. This usage of the RS232 connection is outside of the RS232 specification and may not work in every instance. It is left up to the user to determine if the RS232 output signals will supply enough power for a particular application. Currently, the C2-DB9 uses a MAX3243 or similar driver to convert logic level signals to RS232 level signals. The specifications for the MAX3243 may be used as a rough guide to determine if the signal levels are appropriate for your application. Redpark reserves the right to change the RS232 driver circuitry at any time.

The rear panel of many Rotel models include an RJ45 connection labeled "Computer I/O". This connection is used for serial RS232 control from control systems such as Crestron or Control4, or to upgrade the internal software in the unit. A special RJ45 to DB9 conversion cable is required in order to connect from a standard DB9 serial connection. Many Rotel products include this cable, or it may also be available through the local Rotel authorized dealer or distributor.

HI920011 is a 5 to 9 pin RS232 serial cable for PC connection that allows for easy data transfer from a variety of Hanna meters. The HI920011 has a 9 pin female RS232 connector on one end and a 5 pin DIN female connector on the other end. The serial cable is for use with the Hanna Instruments portable turbidity meters and the HI9829 Multiparameter Meter which are used to test drinking water and ambient water to meet government standards, and to monitor water used in the manufacture of food and beverages.


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