Rockwell Automation 6008-SI IBM PC I/O SCNNR 6008-SI - Manual (Page 126)

Chapter 11
Troubleshooting
11-3
Problem: Possible Solution:
Discrete I/O is updating,
but block transfers are not
Make sure you are addressing the proper module by using this
formula: Module address = rack * 16 + slot #
Check the your program to make sure that the code for block
transfer to that module exactly follows the examples in chapter 8.
Make sure that block transfer length is specified in the block transfer
(QBT) data packet.
Use the U_D1 program to try block transfers. If they execute
properly, the fault is most likely your program.
Block transfers are
working erratically
Declare the QBT data packet as static". Use a different data packet
for each block transfer.
Adapter READY" lights
blink briefly, then go out
Make sure your program is using the host_active macro as
described in chapter 5, "Host Watchdog".