Model 253 Application Notes

The heavy manufacturing environment is replete with examples of machine tools, instruments and other devices being employed and often under the control of a PC. Such control can be effected by linking the PC and these devices by data communications. However, interface conversion is usually needed to effect the communications. Data generally comes into and out of the PC through an RS-232 interface. On the other hand the tools, instruments and other devices may employ the RS-422 interface, which uses differential signaling to combat the high electrical noise prevalent when high current machinery is in operation.

Interface conversion must be carried out in order for PCs using RS-232 communications to be brought into factory RS-422 based communications networks.

The Model 253 Non-Powered RS-232 to RS-422 converter is a convenient device for performing this interface conversion. It carries out conversion for full duplex signals at data rates up to 19.2 KBPS. It needs neither AC nor DC power for operation. Rather, it powers itself from the signals at the RS-232 interface. It provides operation over 8,000 feet of twisted pair cable into a load of 120 Ohms. Finally, it conveniently plugs into the 9 pin DB9 data port found on the back of a PC.

The illustration above shows a ready application of the Model 253. This is the industrial environment with a PC on the left communicating with a machine tools on the right. RS-422 based communications is desired because of its resistance to interference. The machine tool has the RS-422 interface built-in. The PC does not. The Model 253 plugged into the 9 pin RS-232 data port of the PC effects the needed interface conversion from RS-232 to RS-422.


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