Tandy 102 Service Manual page 34

RS-232C Interface Circuit
In the RS-232C transmission circuit, after the DC component is removed from the signals by the
coupling capacitors, the signals are leveled to ±5V signals by the inverters connected in
parallel, and then are output as RS-232C transmission signals.
In the RS-232C reception circuit, the DSRR, CTSR, and RXR signals from the external RS-232C line
are subjected to waveform shaping and inverted by M24, and then converted to +5V or ground level
signals by the diodes.
(
0
GND 1
Z 2
0 TXR
RTSR
DTRR
DSRR
CTSR
RXR
GND
4
20
6
4584
i2 _ -- 13 --- -1 VDD
35 1 R751
0
0K R73 33K
2 1
R9 33
0
n 110
35
11
R9433
35
I 4 3
35
18
35 9
R99 330n]
R89
6.2K
5
35
R74 33K
C71
o. 039)1
R7 1OOK R76 33K
M13 (pin8)
M 38 (pin 13)
M 25 (pin
35)
M 33 (pin11 )
R77 33K
C72
0.039
)L
R81 1OOK R79 33K
R80 33K
C 73
O.O39.
R65
DTR
VEE
13 2 12
1
R137
i00K
R96 18K D9
5 R8 6.2K 9 24 8
I
R138 1OOK
R9 18K D10
3 R87 6.2K 11 24 10
R139 1ooK
7 I
I
D8
R9218K L ---------
VEE
33K VDD
M33
(pin
5)
M 33 (pin
2)
Figure 4-16. RS-232C Interface Circuit