Tandy 1400LT - Switching Logic (RS232 C. MODEM); Baud Rate Generator (1.8432 Mhz)

The UART (IC35) contains a programmable Baud Rate Generator.
The output frequency of the Baud Rate Generator is 16x the baud rate
[ divisor # = (frequency input)/(baud rate
X 16)]. Two 8 bit latches store the divisor in a 16 bit binary format. These Divisior latches must be loaded during
initialization in order to ensure desired operation of the Baud Rate Generator.
Table 4-10 shows the use
of the Baud Rate Generator with crystal frequency of 1.8432 MHz .
m
m
Percent En or Difference
Between Desired and
Actual
Divisor Used to
Generate
16 X Clock
Desired Baud Rate
SELECTOR Hr
B
, ti MODm
50
75
110
134.5
150
300
600
1200
1800
2000
2400
3
600
4800
7200
9600
2304
1536
1047
857
768
3 84
192
96
64
58
48
32
24
16
12
-
0.026
0.058
-
0.69
Table 4-10. Baud Rate Generator (1.8432 MHz)
TO RS232C CONNECTOR / TO MODEM CONNECTOR SWITCHING CIRCUIT
The switching circuit is generated in the GATE3. MOD/m signal is selectable by the software. Figure 4-40 shows
the block diagram of GATE3 (Switching logic)
GATE3
RTS l2 A
TXD l2 A
SELECTOR DTR l2 A
TXDM
m
DO - D7 $1 DE C 0 DER
1/0 PORT
Figure 4-40. Switching Logic (RS232C, MODEM)
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