Radio Shack TRS-80 Service Manual page 11

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POWER
SUPPLY
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POWER
SUPPLY
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CASSETTE
I/O
I/O BUS
Z·80
4K or 14K ROM
4K, 16K, 32K,
or
48K RAM
REAL TIME CLOCK
UPPER/LOWER CASE VIDEO
500/1500 BAUD CASSETTE INT.
KEYBOARD INTERFACE
LINE PRINTER INTERFACE
I/O BUS INTERFACE
LINE
PRINTER
PORT
II
RS·232
I/O
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, , • I
RS'232C
INTERFACE
(optional)
II
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FLOPPY
DISK
CONTROLLER
(optional)
TO
EXTERNAL
DISKS
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DISK
#0
(optional)
DISK #1
(optional)
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BRIGHTNESS
AND
CONTRAST
FIGURE 1. TRS·80 MODEL III BLOCK DIAGRAM