Allen-Bradley PLC-5 User Manual page 141

Status Field Word(s)
Transmit confirm 24
Transmit NAK full 30
Transmit NAK misc. 25
Transmit not ACKed 27
Transmit NAKed SAP 31
Description
Number of SDA messages successfully sent to and acknowledged by the addressed station
Number of times the station received a NAK to a message because the destination station was
full
This indicates that messages are being sent to the receiving station faster than the PLC-5
controller can process them. Most likely, more than one station on the DH+ link is sending
messages to the same station. Check to see that you are:
not scheduling unnecessary traffic (e.g., your are sending continuous messages when you only
need updates once per second)
implementing report-by-exception so that data is sent only if it is new data
Number of incoming SDA messages that were NAKed due to reasons other than the NAKed full
and NAKed inactive counters (e.g., a NAK due to a bad CRC)
Number of SDA messages that were sent but were not ACKed by the receiving station
The following could have occurred:
message could have been NAKed
an invalid ACK was returned
nothing was returned
This counter can indicate:
a noise or a cabling problem
the receiving station has been removed from the link
the receiving station cannot communicate
Number of SDA messages that were successfully sent to but were NAKed by the addressed
station because the SAP specified in the message was illegal
This counter should always be 0.
Communicating with Devices on a DH+ Link
Publication 1785-UM012D-EN-P - July 2005
9-9