Data Transfer File Instructions
Chapter 12
124
Externally Indexed Counter
When the counter is externally indexed, the accumulated value must be
positioned to point to a word in the file by instructions in the user program.
The counter can be indexed randomly by using a Get/Put transfer or
sequentially by using another counter. In either case, the other instructions
are addressed to the accumulated value of the file instruction counter.
Instructions with externally indexed counters will operate when the rung
condition is true. As long as the rung is true, the operation will take place
each scan. If the counter accumulated value (position) changes while the
rung is true, the data at the new position will be operated upon.
An example of a file instruction with an externally indexed counter is
shown in Figure 12.3.
Figure 12.3
Example
of an Externally Indexed File Instruction
WORD-TO-FILE
MOVE
COUNTER ADDR:
212
POSITION: 007
FILE LENGTH: 012
WORD ADDR:
113
FILE R: 420-423
212
(DN)
15
Internally Indexed Counter
An example of a file instruction with an internally indexed counter is
shown in Figure 12.4. The instruction contains an enable bit in addition to
the done bit.
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