DUAL PORT RS-232↔422/485 SERIAL INTERFACE
2.4 Technical Description
The Dual Port RS-232/422/485 Serial Interface utilizes the same 16550 UART chip found in the IBM® asynchronous adapter. This chip features programmable baud rate, data format, and interrupt control. Refer to the IBM Technical Reference for details on programming the chip.
RS-232
The Dual Port RS-232/422/485 Serial Interface meets the RS-232C specifications and provides an asynchronous serial I/O port. This is the standard port configuration found in the IBM AT® computer, including the DB9 style connector.
The table below shows the connector pinouts for ports J1 (port 1) and J2 (port 2) on the Interface while using RS-232.
Pin Number | Signal Name | Mode |
3 | Transmit Data (TD) | Output RS-232 |
7 | Request To Send (RTS) | Output RS-232 |
4 | Data Term Ready (DTR) | Output RS-232 |
5 | Ground (GND) | –––––––––––– |
2 | Receive Data (RD) | Input RS-232 |
1 | Data Carrier Detect (DCD) | Input RS-232 |
6 | Data Set Ready (DSR) | Input RS-232 |
8 | Clear To Send (CTS) | Input RS-232 |
9 | Ring Indicator (RI) | Input RS-232 |
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RS-422
RS-422 allows very long distance communications—4000 feet (about
1219 meters) at 9600 baud—based on use of Category 3, UTP, or better, with virtually error-free differential drive characteristics. RS-422 signal levels are the standard electrical specification used in RS-449 and EIA-530. This allows interfacing with equipment that meets these specifications.
