Publication 1747-RM001G-EN-P - November 2008
13-18 SLC Communication Channels
For processors running OS Series C, FRN 6 and higher, clicking the Clear
button while monitoring Channel Status of either channel 1 or channel 0
online, will reset all of the channel status diagnostic counters for both channels
to zero. Prior to OS Series C, FRN 6 the only channel status diagnostic
counters that are reset when the Clear button is clicked are the ones on the
channel that the programming terminal is connected to. For example, if your
programming terminal is connected online via channel 0 and you are
monitoring the Channel Status of channel 1, when you click on the Clear
button, only channel 0 diagnostic counters will be reset, not channel 1
diagnostic counters.
Global Status Word Overview
When a processor passes the DH+ token to the next node, it can also send a
16-bit word called the Global Status Word (GSW). Every node on the network
sees the token pass message, but only the “next” node on the network accepts
the token. However, all of the nodes on the network read the Global Status
Word sent with each token pass and save it to memory. Each processor on the
DH+ network has a table in memory to store Global Status Word(s) it receives
from other nodes. In each SLC 5/04 processor’s status file, there is a
designation for the:
• Global Status Word.
Data Sent
with
Acknowled-
gement
(SDA)
Transmit failed 25 Number of SDA messages sent by the station that were determined to be in error. This
counter is the sum of the SDA transmit not ACKed and SDA transmit time-out counter.
Transmit NAK full 26 Number of times the station received NAK to a message because the destination station
was full. This indicates that messages are being sent to the receiving station faster than
the processor 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 (for example, you 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.
Transmit NAKed SAP 27 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.
Data Sent
without
Acknowled-
gement
(SDN)
Transmit confirm 28 Number of valid SDN messages sent by the station.
Transmit failed 29 Number of SDN messages sent by the station that were in error. This error should never
be seen.
Received 31 Number of valid SDN messages received.
Table 13.5 SLC 5/04 Channel 1 DH+ Channel Status (Continued)
Status field Word Displays the
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