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3-36 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual
–
May 2002 GFK-1541B
3
Communications Status Words
The COMMREQ Status word (CRS word) and the first word of the two Detailed Channel Status
words (DCS words) report status and errors in the same format, as shown below. The second
word of the DCS words indicates when the channel is active.
The CRS word location is specified in Words 3 and 4 of the Command Block. The DCS words
location is specified in the Retrieve Detailed Channel Status Command. The contents of these
status words are defined below:
The initial value of the Detailed Channel Status words is all zeros. DCS words are reset to zero
when:
The Ethernet Interface is powered up or restarted
The CPU transitions from STOP to RUN
A channel abort COMMREQ aborts the channel
Format of the COMMREQ Status Word (CRS Word)
Hex Format
High
Low
00 00
Minor Error Codes (high byte)
Success and Major Error Codes (low byte)
CRS Word in
Format of the Detailed Channel Status Words (DCS Words)
High
Low
00 00
Minor Error Codes (high byte)
Success and Major Error Codes (low byte)
0000
Channel Active (0001 = channel active,
0000 = channel not active)
DCS Word in Hex Format
Word 1Word 2
There are several points to remember when interpreting the contents of the COMMREQ Status
word and Word 1 of the Detailed Channel Status words:
1.
Display the Status Words in hexadecimal form
to more easily differentiate the high and low
bytes. A good way to do this is to use a MOVE WORD function block to display the
hexadecimal value within the ladder program.
2. The Ethernet Interface will never send a zero for the COMMREQ Status word to the PLC
CPU. The user program should zero the COMMREQ Status word
before
issuing the
COMMREQ function and then check for a non-zero value indicating that the Ethernet
Interface is responding to the COMMREQ. A good way to do this is to use a MOVE WORD
function block to zero the CRS word.