DUAL PORT RS-232 SERIAL INTERFACE
2.4 Technical Description
The Dual Port RS-232 Serial Interface provides the PC/XT™/AT/80X86 computer with two additional serial ports for terminals, modems, printers, etc. The Dual Port RS-232 Serial Interface can be configured as COM1: through COM4:, or any other I/O address.
The Dual Port RS-232 Serial Interface (IC110C) 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. The IC174C uses the 16950 UART chip.
Each serial port can be set as COM1:, COM2:, or any other I/O address set up to 3FF hex, providing total compatibility with most communications software and languages. Some software packages require the use of the modem handshake signals such as CTS or DCD. Consult your software manual to determine handshake-signal requirements. If no requirements are mentioned, or if you are not sure, a safe configuration is to connect (in your cable hood) DTR to DSR and DCD, and tie RTS to CTS. This usually satisfies the modem signal requirements for most communications software.
The table on page 5 shows the connector pinouts for ports J1 and J2 (DB9). Note that this is the same RS-232 pinout as the DB9 serial AT connector.
