Cassette Interface Circuit - Tandy 102 Service Manual

Cassette Interface Circuit
The cassette interface circuit is subdivided into three sections:
• Write circuit
• Read circuit
• Remote circuit
Write Circuit
The write circuit is accomplished in several steps. First, the serial data from the SOD terminal of the
CPU is inverted by M34. Then, the DC component is removed by C63. Finally, the data
passes through an integrator consisting of R51 and C64, and after voltage division, out to a
cassette recorder AUX jack.
Read Circuit
The signal input from the earphone jack of the cassette recorder passes through the clamp circuit
consisting of D5 and D6, and then is input to the comparator circuit consisting of M30.
Finally, the signal is converted into the digital signal and sent to the SID terminal of the CPU.
In this circuit, D7 clamps the negative voltage output of the comparator.
Remote Circuit
As a result of writing data "1" into bit 3 of the output port (Ml 4) specified by I/O address EOH-EFH,
the REMOTE signal is changed to H level.
Then, T6 is switched on and relay RY1 is energized. This causes the drive motor of the cassette
recorder to operate.
0
0
TXC
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C
D: M
5
R54 R51
C63 2 1
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7
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VDD VDD
4584
R95 R52
4584
RXC
4
8
RY 1
10012 1 K
M
13
M30
4
R72
5 6 SID
REMi
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,
n
x
+ 14 33K -
p 11
1 4 5
08
C 0
ti 12
L
REM2
3
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t_ 0
GND 1 I
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GND 6
6 21
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R132150K
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R50
T6
3.3 K
REMOTE
Figure 4-8. Cassette Interface Circuit