6-61
Test 4. 00101101 is loaded and read back via U243. Test result is set to FAIL if not a match on bits 0
through 5.
Test 3. 10010110 is loaded and read back via U243. Test result is set to fail if not a match on bits 0
through 5.
Test 2. 01001011 is loaded and read back via U243. Test result is set to fail if not a match on bits 0
through 5.
Test 1. 10100101 is loaded and read back via U243. Test result is set to fail if not a match on bits 0
through 5.
The test is to load a pattern into the display counters, U220 and U211, with the LDCOUNT strobe. The
counter outputs are switched to the 0 bus through U221, U212, U210 by holding U414A in the reset
mode (PRESTART + DISPLAY is LO). The inputs to U240 are the bits 00 through 05 where 00
through 03
=
O.04 and 05 are the bO,bl data of pattern. To read back properly, one shifts the pat-
tern left 6 bits and uses bits 6 and 7 of XDIAG (U243); the test result is set to FAIL if the test fails.
The test result
=
PASS.
MISC
=
00100000. Significant bit is b5 (ZAXIS OFF).
MODECON
=
00010000. Significant bit is b3 (U240).
DISCON
=
01100000. Significant bits are b2, b5, b6, and b7 (STOPDIS, enable
"0"
bus, not ENV
mode).
Initialization:
This test requires the display state machine to be operative. There is no "good" way to insure that it is
functional, and there have been no previous tests to help find that out. Therefore, if this test fails, it
could be for several reasons other than U240.
If run from this level, all four tests are selected in turn, or one may execute anyone test by selecting
2351 to 2354.
Testing Method:
Readout Buffer U240 (diagram 16):
2350
U240
5b. Verify the COUNTEN chip enable to U140 pin 19 has a HI-to-LO transition; then, before the time
that U140 pin 1 goes LO, U140 pin 19 goes HI. While U140 pin 19 is LO, inputs
06, 07,
08 are
selected. If ok to here, replace U140.
Sa. Verify the RO chip enable to U140 pin 1 is HI for about half of the Trigger strobe positive period,
and then that it goes LO and stays LO for the remaining time. This LO selects inputs 06 through
09 of U140.
4. Verify the outputs of U221, U212, and U210 are stable and correct after the LDCOUNT strobe to
the previous bus.
3. Verify that U323 pin 3 is LO.
Table
6-6
(cont)
Maintenance-2430 Service
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