Rockwell Automation 1771-DCM USER MANUAL 1771-DCM - Manual (Page 47)

Calculating Transfer Time
Chapter 7
7Ć13
You have a communications problem.
You did not correctly connect the twin-axial cable to the scanner.
You did not connect a terminator resistor to each end of the twin-axial
cable.
When the scanner encounters a communication fault, it tries twice to
complete the transfer. It sets the error bit after the second unsuccessful
try.
When the scanner and/or processor detects a block transfer error, the
transfer is halted. Transfers from that module are prevented until:
Your program clears the instruction’s control word (clears the error,
Figure 7.5).
You locate and correct the error.
Figure 7.5
Resetting the Control Word after a Block Transfer Error
MOV
Move from A to R
A : Storage Word
0000000000000000
R : Control Word
0000000000000000
13
03
Control Word