4
FOUR PORT RS-232 SERIAL INTERFACE
2.4 Technical Description
The Four Port RS-232 Serial Interface provides four additional serial ports for
terminals, modems, printers, etc. The Serial Interface can be configured as
COM1: through COM4:, or as any other I/O address (up to 3FF Hex),
providing total compatibility with most communications software and
languages. The Four Port RS-232 Serial Interface (IC111C) uses the 16550
UART chip, which features programmable baud rate, data format, interrupt
control, and a 16-byte FIFO. The IC181C uses the 16850 UART.
Modem Control Signal Considerations
Some software packages require the use of the modem handshake signals
such as CTS or DCD. Consult your software manual to determine the
requirements of your modem control signals. If no requirements are
mentioned, or if you are not sure, a safe configuration is to tie DTR to DSR
and DCD (6-8-20), and tie RTS to CTS (4-5). This will typically satisfy the
modem control-signal requirements for most communications software.
Pin Number Signal Name Mode
2 Transmit Data (TD) Output RS-232
4 Request To Send (RTS) Output RS-232
20 Data Term Ready (DTR) Output RS-232
7 Ground (GND) ––––––––––––
3 Receive Data (RD) Input RS-232
8 Data Carrier Detect (DCD) Input RS-232
6 Data Set Ready (DSR) Input RS-232
5 Clear To Send (CTS) Input RS-232
22 Ring Indicator (RI) Input RS-232
Table 2-1. P1 through P4 pinouts as found on the
octopus cable (standard RS-232C DTE)
