Radio Shack TRS-80 26-3650

3-3.
CPU
Signal
Descriptions
Pin
No.
Signal
Name
In/Out
Function
1~4
D1
-
D8
In/Out
Data
bus.
Also designates RAM
address
while
signal OP is
HIGH.
5
INT
Not
used.
6~
18
KI2-
K1
In/Out
Key
input/output signals.
19
SW
In
Power switch input
signal.
20-24
V5-
V1
In LCD
drive voltages. These voltages
are
generated by
connecting external
resistors
to
VDD2.
25,
26
OSO,
OSI
In/Out
By
connecting
56
kohm external
resistance
between these
terminals, clock pulse is
inter-
nally generated.
27-72 R15-
R7
Out
LCD
display signals.
73
GND
In
(zero) volt
power source.
74,
75
CE1, CE2 Out Chip
enable signals. CE1
selects
RAMI
at
HIGH level while CE2
designates
RAM
2 at
HIGH level.
76
VDD1
In
—5.5V
input.
77
VDD2 Out —5.5V output
from
the LSI.
Stays
-5.5V
at
power ON. Goes
to 0V at
power-off)
or APO
(Auto
Power-Off).
78,
79
01,
02
Out
Clock pulses.
80
OP
Out When the signal
is
H IGH,
the data
bus becomes
address
bus
for RAMs and
also
becomes
the
command code for the optional cassette tape
interface.
-
5
-