Troubleshooting Procedures; Scoping Loops - Texas Instruments 990 Maintenance Manual

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945407-9701
5.4 TROUBLESHOOTING PROCEDURES
Upon receipt of a defective data module from a field repair facility, inspect the module for
visible signs of damage (loose or missing components, loose or missing jumpers, breaks in the
board or etched circuits, foreign material which may have caused short circuits, etc.). If no
indications of damage are found, place the module on an extender card in the hot mock-up
system and perform the procedures listed in table 5-1.
5.4.1 SCOPING LOOPS. A scoping loop is a short repetitive software program which establishes
and maintains a set of conditions in the circuitry under observation so that an error of brief
duration may be observed and isolated. Once the malfunction has been discovered, a scoping
loop is entered into the hot mock-up computer from the programmer panel on either the
computer chassis or the Model 990 Maintenance Unit. The scoping loop permits data to be
written into or read from a desired memory location or block of memory locations. Dynamic
troubleshooting may then be performed in accordance with the procedures in table 5-1. Table 5-2
provides a reference for tracing each output line circuit, and table 5-3 provides a reference for
tracing each input line circuit.
The following scoping loop is used to set a CRU output line to 'l' and to read back the corre-
sponding CRU input line. The normal indication is that CRUBITIN-
=
CRUBITOUT.
Main Memory Location
Machine Code Comments
1000 C300 MOY 0.12 (Move the CRU base
address to register 12)
1002 1D09 SBO 9 (Set CRU output line '9'
to 'I')
1004 0206
LI 6,>oo40 (Load register 6 with
1006 0040
004016)
1008 0606 DEC 6 (Decrement register 6
by one)
IOOA 16FE JNE $-1 (Loop until register
6 = 0)
IOOC 1F09
TB 9 (Test CRU input line 9)
IOOE 10F8 JMP $-7 (Go back to the beginning
of the loop)
1040
xxxx
Enter the CRU base address.
WP= 1040
PC= 1000
5-4
Digital Systems Division