Rs-232C Technical Description - Radio Shack TRS-80 Model 4 Technical Reference Manual

9.1 RS-232C Technical Description

The RS-232C option board for the Model 4 computer
supports asynchronous serial transmissions and
conforms to the EIA RS-232C standards at the input -
output interface (P1). The heart of the board is the
TR1602 Asynchronous
performs the job of converting the parallel byte date
from the CPU to a serial data stream including start,
stop, and parity bits. For a more detailed description
of how this LSI circuit performs these functions, refer
to the TR1602 data sheets and application notes.
The transmit and receive clock rates that the TR1602
needs are supplied by the Baud rate generator
(BR19411). This circuit takes the 5.0688 MHz
supplied by the CPU board and the programmed
information received from the CPU over the data bus
and divides the basic clock rate to provide two clocks.
The rates available from the BRG go from 50 Baud to
19200 Baud. See the BRG table for the complete list.
NIBBLE LOADED
0H
1H
2H
3H
4H
5H
6H
7H
8H
9H
AH
BH
CH
DH
EH
FH
RS-232C CIRCUIT BOARD
Receiver/Transmitter.
BRG PROGRAMMING TABLE
TRANSMIT OR RECEIVE
BAUD RATE
50
75
110
134.5
150
300
600
1200
1800
2000
2400
3600
4800
7200
9600
19,200
It
16X CLOCK FREQUENCY
2.1523kHz
32.081 kHz
115.2kHz
153.6kHz
307.2kHz
87
SUPPORTED BY
0.8kHz
1.2 kHz
1.76kHz
2.4kHz
4.8kHz
9.6 kHz
19.2 kHz
28.8kHz
38.4 kHz
57.6kHz
76.8 kHz
SETCOM
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes