User manual

Operating Your PLC-5 Backup System
Chapter 5
5-17
For example, if the primary processor is sending multiple blocks to the
secondary processor, the data that was in block 2 when block 1 was sent may
change by the time block 2 is sent. This is because the ladder program,
which executes asynchronously to block transfer instructions, may have
changed the information in block 2 before it was sent.