4
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
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.
