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Communications Status Words
The COMMREQ Status word (CRS word) and the first word of the two Detailed Chan- nel Status words (DCS words) report status and errors in the same format, as shown be- low. 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 con- tents 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:
HThe Ethernet Interface is powered up or restarted
HThe CPU transitions from STOP to RUN
HA channel abort COMMREQ aborts the channel
CRS Word in
Hex Format
High Low
00 00
Minor Error Codes (high byte)
Success and Major Error Codes (low byte)
Figure 4-3. Format of the COMMREQ Status Word (CRS Word)
DCS Word in Hex Format
Word 2 | Word 1 | |
| High | Low |
0000
00 00
Channel Active (0001 = channel active, 0000 = channel not active)
Minor Error Codes (high byte)
Success and Major Error Codes (low byte)
Figure 4-4. Format of the Detailed Channel Status Words (DCS Words)
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
Chapter 4 Programming Communications Requests |
