IBM PC 100, Техническое руководство

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Chapter 2. Connectors and Jumpers
Serial Port Connectors
The two serial connectors on the back of the computer use a 9-pin, male, D-shell connector and pin
assignments defined for RS-232D. The voltage levels are EIA only. Current loop interface is not
supported.
1 5
6 9
The following figure shows the signal and pin assignments for the serial port connector in a
communication environment.
Use Serial A or Serial B for high-speed modem and printer connections, or for devices such as a mouse
or other pointing device.
The serial ports transfer data one bit at a time (serially) at speeds ranging from 300 to 345 600 bits per
second (bps). The transfer rate is also referred to as
baud rate. The serial ports on the computer are
16550-UART (universal asynchronous receiver/transmitter) compatible which means that they can support
high-speed modems.
Serial-Port Setup
Each serial connector or adapter in the computer can use any of four available port settings, provided that
a different setting is used for each. The settings include the port address (in hexadecimal) and the IRQ
(interrupt request line), which determines how the microprocessor responds to an interrupt from the serial
port. The four available port settings, in sequential order, are:
3F8h-IRQ 3 or 4
2F8h-IRQ 3 or 4
3E8h-IRQ 3 or 4
2E8h-IRQ 3 or 4
There is no direct relationship among the port connectors, the four available port settings, and the four
COM numbers. When the computer is started, the power-on self-test (POST) assigns COM numbers to
the port addresses that are actually in use at the time. POST goes down the list of addresses sequentially
to assign COM numbers to each address in use by a serial device. If an address is not in use, a COM
number is not assigned. POST assigns the next available COM number to the next address in use. The
port addresses and IRQ for Serial A and Serial B are preset at the factory to:
Serial A: 3F8h-IRQ 4
Serial B: 2F8h-IRQ 3
POST assigns COM numbers to Serial A and Serial B during startup, as follows:
Serial A: 3F8h-IRQ 4 (COM1)
Serial B: 2F8h-IRQ 3 (COM2)
Figure 23. Serial Port Connector Signal and Pin Assignments
Pin I/O Signal Name Pin I/O Signal Name
1 I Data carrier detect 6 I Data set ready
2 I Receive data 7 O Request to send
3 O Transmit data 8 I Clear to send
4 O Data terminal read 9 I Ring indicator
5 NA Signal ground
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Technical Information Manual