Data Table
Chapter 3
315
additional 7 timer/counter instructions become available. The previous
output image table addresses 020
8
-026
8
are now reserved for timer/counter
accumulated values; previous input image table addresses 120
8
-126
8
, for
timer/counter preset values.
When I/O requirements are increased from the standard value of 256 to
384 (or from 2 racks to 3 racks), data table size does not change. Instead,
timer/counter areas (in the default memory configuration) are each
reduced by 8 words. Previous timer/counter accumulated value addresses
030
8
-037
8
are now reserved for output image table; previous timer/counter
preset value addresses 1308-1378, for input image table.
When I/O image table size is increased from 384 to 512 (i.e., increase
from 3 to 4 racks), timer/counter areas are reduced by another 8 words.
Previous timer/counter accumulated value addresses 040
8
-047
8
are
reserved for output image table. Previous timer/counter preset value
addresses 1408-1478 are reserved for the input image table. This same
progression continues, as follows:
when you increase the I/O to 640 (5 racks), accumulated address limits
become 060
8
to 077
8
and the preset address limits become 160
8
to 177
8
.
when you increase the I/O to 768 (6 racks), accumulated address limits
are 070
8
to 077
8
and preset address limits are 170
8
to 177
8
and with the maximum I/O increase to 896 (racks), accumulated address
limits and preset address limits are completely gone from the default
data table.
Data table expansion becomes necessary if 7 racks are selected and timers
or counters are desired. The first address available for accumulated storage
would be 200
8
and the first preset address would be 300
8
.
NOTE: Block transfer counter addresses must start immediately following
the I/O address. Therefore, if the I/O image table size is changed, the block
transfer instructions must be reprogrammed.
Memory Write Protect
In the processor, the inhibit feature is active when the user removes a
jumper from the 1772-LH interface module. This prohibits alteration of the
user program in any processor mode. The alteration of data table words
4008 and above is also prohibited except through the user program. Only
data table values between word addresses 010
8
and 377
8
can be changed
either in run/prog or prog modes.
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