Radio Shack TRS-80 Service Manual page 18
Pocket computer printer and cassette interface
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Also See for TRS-80:
- Reference manual (274 pages) ,
- User manual (236 pages) ,
- Service manual (199 pages)
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5)
Timer/cou
nter
circuit
PC
.
5
C2
PC4
'
0
PC3
...
0
PCI
"'
-l
Cl
"
co
"O
0
"'
STB
"'
0
~
cs
;,..
(")
"'
()Q
f'CoO
PC2
DATA
HI
~
PS6
CNO
PBS
Yoo
XTAL
XTAL
O
E
TP
DATA
OUT
Cl.K
Vee
1---~a
32.768kH1.
y
1. Outline
As shown
in
the left,
the
µPD I 990AC
is
used
for
the
time
keeping
JC
to count
hour/minute/second/ml)nlh/day.
2.
Main
function
of
µPD1990AC
Time data
is in the BCD
form
and is
judged by means of
comparison.
How-
ever,
day of week
is
nol used with
this
chip and
hou
r
is
represented
by
24-hour
system.
r
-
--
----
~-+-+-~~~~~~~~--'
,
Vee
:
:
+
I
'-
-
...
-
-
-
-·
110
CPU
Reset
ILS&I
IMS&!
OIN
2
5
2
B
~
Seconds
M
inutes
Houn
Dav
Week
Month
•
I
•
•
I
4
I
4
4
Bits
Bits
Bits
8iu
Blu
Blc:s
•
I •
S
its
Sib
•
I
•
Bits
Bits
Pin
Signal
In/out
Description
No.
N:une
I
C2
Jn
'Mode
select
signal
C2=0
2
Cl
ln
Mode select signal
Cl
co
Mode
Data
In/out
mode
3
co
In
Mode
select signal
0
0
0
Regi!ler
hold
0
I
I
Register
shift
I
0
2
Time
set
I
I
3
Time read
4
STB
In
St
robe.
Command
is latched
by
t
he
strobe
STB.
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