Rockwell Automation 1771-DB Basic Module User Manual - Series A - Manual (Page 142)

Programming
Chapter 6
6–10
1. The block lengths PUSHed for CALLs 4 and 5 must equal the
corresponding lengths on your BTW/BTR instructions in the processor.
2. If a BTW appears first in your ladder logic, put CALLs 3 or 6 first in your
BASIC program. If a BTR appears first in your ladder logic, put CALLs
2 or 7 first in your BASIC program.
3. Set the PLC-5 block-transfer-write timeout bit (block-transfer control
block, word 0 bit 8) to eliminate excessive PLC-5 scan times. When the
timeout bit sets, the processor attempts two DB block-transfers before
generating a block-transfer error. The error condition resets the enable bit
and restarts the block-transfer in our program example, figure 6.7.
4. If your application requires bidirectional block-transfers, you can use
CALL 6 or 3 and CALL 7 or 2 as necessary if:
you use an equal number of each type.
you alternate their use (e.g. CALL 6, CALL 7, CALL 6, CALL
7)You can put the calls anywhere in the program. They can occur
at any time interval.
5. If your application requires a one way block-transfer (all
write-block-transfers or all read-block-transfers, use only the associated
CALLs (4, and 3 or 6; 5, and 2 or 7).
6.6.
Block-Transfer
Programming Tips