Rockwell Automation 1771-DB Basic Module User Manual - Series A - Manual (Page 135)

Programming
Chapter 6
6–3
Refer to figure 6.1 for the sample ladder logic and figure 6.2 for the
corresponding BASIC program. The values shown in figure 6.2 are for
demonstration purposes only. Use the program shown in figure 6.2 for all
PLC-2, PLC-3 and PLC-5 processor ladder logic programs shown in this
chapter. Figure 6.3 is an actual sample program.
Figure 6.1
Sample PLC-2 Family Ladder Logic
6.3.1.1
Rung Description
Rungs 1 and 2 – The first two rungs of the sample program toggle the
requests for block-transfer-writes (BTW) and block-transfer-reads (BTR).
The interlocks shown do not allow a BTR and BTW instruction to enable
at the same time.
Rung 3 – When a BTR successfully completes, its done bit sets, enabling
the file-to-file move instruction. The file-to-file move instruction (FFM)
moves the BTR data file (File CCC-DDD) into a storage data file
(EEE-FFF). This prevents the programmable controller from using invalid
data if a block-transfer communication fault occurs.
6.3.1
PLC-2 Processor Program
(continued)