Back then, RS232 was preferred for connecting computers and Programmable Logic Controllers (PLC) with the peripherals such as printers, mice, and modems. It is the most commonly used serial communication protocol in the industry. RS232 is also commonly used in debugging tools such as JTAG adapters.īeing one of the EIA standards, RS232 is also known as the EIA232 protocol. The simplicity of the RS232 interface makes it widely used in a variety of applications including industrial control, barcode scanners, and GPS receivers. RS232 is an asynchronous protocol, meaning that it does not require a clock signal to synchronize data transfer. The receiving line is used to receive data from the TX line. Data is transmitted serially, meaning that each bit is sent one after the other on the TX line. The protocol uses a simple three-wire interface consisting of a transmit (TX) line, a receive (RX) line, and a ground (GND) line. RS232 is a standard for serial data communications between computers and other devices. What is the Speed and Baud rate of the RS232 protocol?.If you would like to buy the Keyspan USA-19HS USB-to-Serial adapter, you can get it at Amazon. If you’re in need of purchasing an IDC10-to-DB9 serial adapter, ether model can be purchased at AT/Everex and DTK/Intel. If you would like to learn more about RS-232, check out this Wikipedia page. I’m a happy administrator.Īnd just to be complete, here was the final configuration settings I used in nf: # nf v1.1 # Finally, the server was powered through the UPS and accurately monitored via apcupsd. Even quicker, I warmed up the soldering iron and re-wired my adapter in less than ten minutes. A quick fix was to buy the correct adapter. Once I discovered that there were two industry standard conventions in use for the IDC COM header connector pinout, my problem was solved. The following tables detail the differences: DB9 Connector AT/Everex was known as Straight Through Wiring, and DTK/Intel ws known as Cross Over Wiring. They were known as AT/Everex and DTK/Intel. This was unreliable, so I wanted to figure out what the problem was with my serial connection.Īfter a bit of research, I learned that there were two pinout conventions used for the IDC10 header on motherboards. The next time the server rebooted, it could have been ttyUSB1. The problem with this setup was that I couldn’t rely on the device always being ttyUSB0. I also explicitly define DEVICE as /dev/ttyUSB0. Instead, I define UPSCABLE as the model number of the proprietary APC serial cable I’m using, 940-0024C, and UPSTYPE as smartups. In the following configuration, notice that UPSCABLE and UPSTYPE are not configured as usb. However, when using the Keyspan USB-to-serial adapter, nf needed to be configured differently. This is because apcupsd will try all the known USB ports until it succeeds. Note that UPSCABLE and UPSTYPE are configured as usb and DEVICE is not defined at all. For a typical USB configuration, nf would be setup as follows. When using the Keyspan adapter, the only caveat is that communication with the UPS is configured as using a serial cable instead of a USB cable. I’m using apcupsd to monitor the UPS and control the server during a power outage. So before discovering and solving this problem, I setup the UPS with a Keyspan USA-19HS USB-to-serial adapter, which I thought would be an easy fix. Initially, I had communication problems as a result of purchasing the wrong IDC10-to-DB9 serial adapter. I did, however, own one of their proprietary serial cables, part number 940-0024C, so that’s how I set things up. Although this UPS is capable of USB communication, APC uses a RJ45 connector on the back of the unit, and I didn’t own one the correct cable. I’m in the process of building a server with Ubuntu 12.04, and I needed a serial connector to communicate with an APC Smart-UPS RT 1500VA RM. If you want to know more about how I discovered this and the differences, then continue reading. I had just such a need recently and discovered that there are two industry standard pinout conventions in use, the AT/Everex and the DTK/Intel. If you have a need for a serial port, then an IDC10-to-DB9 serial adapter might be required. With servers, however, the serial port is still in use, but sometimes it’s only available as an IDC COM header connector on the motherboard. But with USB being a much better protocol and easier to use, the serial port has just about disappeared from modern desktop computers. At one point, the RS-232 9-pin Serial Port used to be a common connector on the back of every computer.
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