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HThe SYSID field of the COMMREQ Function Block defines the target rack and slot of the Ethernet Interface to receive the command data. The first two digits of SYSID (00 in this example) indicate the rack number, the last two digits (04 in this example) indicate the slot number of the Ethernet Interface.
HThe TASK field of the COMMREQ Function Block indicates which mailbox task ID to use for the specified rack and slot. This field should always be zero (0) for the Ethernet Interface.
HThe FT output (CMRQFLT in this example) is turned on (set to 1) if there were problems preventing the delivery of the Command Block to the Ethernet Interface. In this case, the other status indicators are not updated for this COMMREQ.
Note
The OK output is not used in this example so that the sample code can equally apply to a
Troubleshooting Your Ladder Program
As explained in Section 4 of this chapter, there are several forms of status data which can be used in your ladder program. The use of the LAN Interface OK bit in the LAN Interface Status Word was described in the ladder program fragment above. Some of the status data can be used to troubleshoot your program in its developmental stage. The two primary sources of this data are the FT Output on the COMMREQ Function Block and the COMMREQ Status word (CRS word).
FT Output is ON
If after executing a COMMREQ Function, the FT Output is ON, then there is a programming error in one or more of the following areas.
HInvalid rack/slot specified. The module at this rack/slot is unable to receive a COMMREQ Command Block.
HTask ID not valid. (Should be set to 0.)
HData Block length is specified as 0 or greater than 128.
COMMREQ Status Word is Zero (0) and FT Output is OFF
If after executing a COMMREQ function, the CRS word is zero (0) and the FT Output is OFF, then the Command Block has been sent to the Ethernet Interface, but no status has been returned yet. If this condition persists, check the PLC fault table for information.
COMMREQ Status Word is Not One (1)
If after executing a COMMREQ function, the CRS word is not one (1) indicating success, then there were:
HErrors in the Command Block (the Channel Command code or parameters), or
HFor an Establish Read or Write Channel Command, the command parameters were valid but there was an error in establishing a channel.
If the CRS word does not contain a 1 indicating success, then it contains either a 0 or a code indicating what error occurred. See Section 4 of this chapter for CRS word error codes.
Chapter 4 Programming Communications Requests |
