USER MANUAL 1771-DCM User Manual
Using the Status Word
Chapter 5
53
Bit 14 Not Used
Bit 13 No Data Available
Set by the 1771-DCM at power-up. The 1771-DCM rests this bit when it
receives data from the supervisory processor.
Bit 12 Not Used
Bit 11 Inhibit Outputs
Set by the 1771-DCM to inform the local processor that the supervisory
processor has been switched to program or test mode, has switched itself
to program mode because of a dependent I/O fault (PLC-2 family), or that
the 1771-DCM has lost communication with the supervisory processor.
Bit 10 Invalid Data
Set by the 1771-DCM whenever it sets any other status bit. As long as
this bit is reset, the 1771-DCM has detected no error condition or change
in status.
When the 1771-DCM detects an error in its communication with the local
processor, it indicates this condition in the status word read by the
supervisory processor as follows:
17 16 15 14 13 12 11 10
Insuf Excess Backplane Backplane No Old 0 Invalid
Data Data Reset Error Data Data Data
Bits 17, 16, 13, and 10 Same as Local Processor
Bit 15 Backplane Reset
Set by the 1771-DCM to inform the supervisory processor that the local
processor has reset the backplane. The local processor typically resets the
backplane when switched to program/test mode, or when it detects a fault
condition and turns off outputs. The 1771-DCM cannot detect a
backplane reset due to a fault condition resulting in outputs remaining in
last state. You determine the last state condition (hold last state or turn
off) by a DIP switch on the I/O chassis.
Status Bits Read by the
Supervisory Processor