Specifications

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 connectors are the

left-hand 9-pin “D-type” connector mounted on the rear panel

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.”

MD-DOS uses labels to refer to the various 110 ports on your

computer. The RS-232C

serial ports on the system mother

board are assigned the “COM1” (Communications port #l)

label and the second port is “COM2” (Communications port

#2) label.

Unlike serial ports, parallel ports allow your computer to

communicate one entire byte at a time. Eight wires are

included in the cable to permit the transmission of each of the

eight data bits simultaneously. Extra wires are included in the

cable for control signals. Your Computer uses the industry

Expanding

OUY

System

7-3