run the current application software.

Serial Ports

There are two basic kinds of general purpose I/O (Input/Output) port. One kind is a “serial” port, where data bits are sent one at a time along a single wire, in series. Additional wires are used to send control signals between the transmitting and receiving devices. These control signals allow the two communicating devices to determine which of them will send or receive the data, and when the first bit of a particular byte is being sent, among other things.

Standardized “protocols” for these signals have been agreed upon by the microcomputer industry so that the different manufacturer’s machines can communicate with each other.

Your computer system uses the “RS-232C” asynchronous serial communications interface. The serial port connector is the left- hand 9-pin “D-type” connector mounted on the rear pannel of the system motherboard. Electrical information for the serial port is in Appendix A “Specifications.” For details on the serial port pin connections, see Appendix D, “Connector Pinouts.”

MS-DOS uses labels to refer to the various I/O ports on your computer. The RS-232C serial ports on the system motherboard are assigned the “COM1” (Communications port #l) label and the second port is "COM2" (Communications port #2) label.

Expanding Your System

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