Master Schematic Diagram - Radio Shack TRS-80 Reference Handbook

MREQ
240
19 2MREQ
*"
®
(TO Z23, pins 4 and 12)
SEE
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2
KEf
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ROM
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ROM
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AI4
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238
AI5
5
(pi
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10,12,61
GND
29
MREQ
R9
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29
(32 PLACES)
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37
C2 2,C2 3, C29,
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16-C19 C31,C33,C3S-C38,
I
'39
C40,C41, C44-C56
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(Revision D and after)
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RAM·
A. Pins 5 and 4 of Z74 connect directly to signal
~MREQ*.
B. Pins 20 of Z33 and Z34 are tied together.
C. DIP shunt Z3, pins 6,7 and 8 are tied together and go to pins 20 of Z33 and Z34.
The signal is now called ROM*.
D. Pin 39 is now ground. +5 volts still goes to 0.1 MF capacitors (32).
Figure 28. Changes to the TRS-80 Schematic Diagram (Figure 29)
(Revisions D and E)
III