Texas Instruments 990 Maintenance Manual page 34

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945407-9701
NOTE
If the RUN LED fails to light, return to step 1 and repeat the
program setup procedure.
The following scoping loop is used to test all 16 of the output/input lines. As shown, it sends
FFFF
16
out and loops it back on the input lines. The FFFF
16
value is loaded into the interface
by the LDCR instruction from register 2; the 16 bits read back are stored in register 8 by the
STCR instruction. The normal indication is that register 2
=
register 8. By changing the value at
location 1006
16 ,
any value (pattern) may be looped out/in. By changing the count operand of
the LDCR and STCR instructions, any number of lines may be tested.
The loading procedures for this loop are identical to those for the previous example.
Main Memory Location Machine Code Comments
1000 C300 MOY 0,12 (Move the CRU base
address to register 12)
1002·
04C8 CLR 8 (Clear register 8)
1004 02Q2
LI 2 >FFFF (Load register 2
1006
FFFF
with FFFF 16)
1008 3002 LDCR 2,0 (Load the 16 CRU
lines with the data in register 2)
100A
0206
LI 6, 0040 (Load register 6 with
JOOC 0040
004016)
IOOE 0606 DEC 6 (Decrement register 6 by one)
1010
16FE
JNE $-1 (Loop until register 6 = 0)
1012 C300 MOY 0,12 (Move the CRU base
address to register 12)
1014 3408 STCR 8 ,0 (Load register 8 with the
value of the 16 CRU input bits)
1016 IOF4 JMP $-11 {Go back to the beginning
of the loop)
1040
xx xx
CRU base address.
PC= 1000 16
WP= 1040 16
5-8
Digital Systems Division