Cpu Signal Descriptions; Ram - Radio Shack TRS-80 26-3650 Service Manual

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
-