Mitsubishi Electric Apricot LS Pro, Hardware Technical Reference

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Chapter 1
Chapter 2
Chapter 6
Contents
Chapter 3
Chapter 5
System Board
Chapter 3
LS PRO HARDWARE TECHNICAL REFERENCE 3/17
3.8 PERIPHERALS CONTROLLER
A 16C452 peripherals controller provides two serial and one parallel port.
Serial ports
The serial controllers integrated in the 16C452 are fully compatible with the
NS16450 serial communications controller. They automatically add and remove
start, stop and parity bits. Programmable baud rate generators allow operation
from 50 baud to 56 Kbaud. The ports support 5, 6, 7 and 8-bit characters with
1, 1.5 or 2 stop bits. A prioritized interrupt system controls transmit, receive,
error and line status as well as data-set interrupt.
Each serial port controller provides the following functions:
• Full double buffering in character mode
• False start-bit detection
• Line-break generation and detection
• Modem control functions:
Clear to send (CTS)
Request to send (RTS)
Data set ready (DSR)
Ring indicator (RI)
Data carrier detect (DCD)
Note
The DSR, DTR and RI modem control signals of COM2 do not appear on the serial port at
the rear of the system unit.
COM1 is connected to the system address and data busses using IRQ4 while
COM2 uses IRQ3. The controllers occupy a group of eight consecutive I/O
ports COM1 at 03F8-03FFh and COM2 at 02F8-02FFh. The ports have the
following significance.
Location Significance
0 Transmit Data
Receive Data
Baud Rate Generator Divisor (Low byte)
1 Baud Rate Generator Divisor (High byte)
Interrupt Enable
2 Interrupt Identification Register
3 Line Control Register
4 Modem control Register
5 Line Status Register
6 Modem Status Register
7 Scratch Pad Register
Programmable The serial port controllers each contain a programmable baud-rate generator
baud-rate which can divide the clock input (1.8432 MHz) by any divisor from 1 to 65,535. The
generator output frequency of the baud-rate generator is the baud-rate multiplied by 16. Two
8-bit latches store the divisor in a 16-bit binary format. These divisor latches must
be loaded during setup to ensure the correct operation of the baud-rate generator.
When either of the divisor latches is loaded, a 16-bit baud counter is immediately
loaded. This prevents long counts on the first load.