CHARACTER
WRITING
PROBLEMS
CONDITION
POSSIBLE
CAUSE
19.
Characters don't
write
on
the
screen. 1. Duplex
switch
in
"full"
position
when it
should be
in
"half".
1. DAV latch
(1C616)
-
No DAV
signal.
3.
DAV
priority
encoder
(1C61
1A,
C,
D, lC610D, lC619B).
4.
Three-state enables
(1C6088,
C, D).
5. RAM WE. OC
if
DAV timing
pulse (lC737A).
6. RAM
F. OC
if DAV riming
pulse (1C7198,
D).
7. DAV from lC719C, lC725A, lC713C.
8.
Special
character
generator
l@04, 1C405, 1C406 latched
on
(A1
or
A2 high).
20. Wrong characters write
on
the
screen
1. Keyboard
encoder
1C402.
2. Keyboard
buffer
1C403.
3. Bus wires interchanged.
4.
Bus wires shorted to
+
or
ground.
5. Bus
buffers
1C603, 1C620.
6. Shorted bus
foil.
7.
BAUD rate set wrong.
21. Screen filled with same character. 1. RAM
counters
not
counting:
tc722o, D.
tcs02.
tc219F, tc217D.
2. Keyboard
output enable always on:
P402-8 always logic 0.
Check
DAV latch
and three-state enables
tc616. tc608. tc610. tc619.
3.
Parallel input
enable always on: Check
items listed
under
2
above.
4.
UART ilDE enable always on: Check
items listed
under
2
above.
22. Same line is repeated 12
times. 1.
+12
counter not cbunting up.
2. 1c519,lC511C, rcs158, rC716A, rC715C.
23. Blocks
of characters are repeated
left
to
right. 1.
2.
+4
counter
not
counting.
1c513, lc5148,
lcs10C.
24. Writes
two characters. 1. Full Duplex key
set
for half
duplex
(released)
instead of
full
duplex
(pushed
in).
25. Characters write
erratically.
'1.
Wrong baud rate.
26. Misses
characters coming from the
computer.
1. Refresh interrupt not
enabled at the
rear
pqnel
baud
rate
switch. Connect
the
gr6en
wire to lug
2
of SW2
(for
BAUD
rates
great€r
than
600).
2.
At 110
baud, the
computer
may not be
programmed
lor two
stop
bits.
27.
Characters
write in more
than one
position
on the screen. 1. Address
encoder.
1C512, lC526A, lC526D,
& lC527B.
2. RAM address lines shorted or open.
3. Counters
not
counting up
(see
"Conditions
22 & 23" above).
4.
Check
the counter cascade controls.
lC73O,1C724
(+20
+
+4, +4
+
+12, +QQ e +12,
etcl.
28. Writes
control characters.
't.
2.
Control character decoder.
lC703C, lC703B, lC707C, and
tc702.
Control character detector.
lC617A.
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