Rockwell Automation 1771-DCM USER MANUAL 1771-DCM - Manual (Page 21)

Using the Status Word
Chapter 5
5Ć4
Bit 14 Ć Backplane Error
Set by the 1771-DCM whenever it detects that a block transfer operation
by the local processor was not completed on time, was out of sequence, or
contained a checksum error. The 1771-DCM returns the last valid data
received from the local processor. It returns zeroed data words if
communications had not been established. It inhibits block transfers to
the local processor until it detects a backplane reset or a scan from the
local processor.
Bit 12 Ć Old Data
Set by the 1771-DCM whenever it detects that it has not received data
from the local processor after a delay of 14 read scans by the supervisory
processor (discrete data transfer), or since the last read block transfer by
the supervisory processor. The 1771-DCM passes old data to the
supervisory processor until it detects new data, passes it, and resets this
bit.
Bit 11 Ć Not Used