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TCP/IP Ethernet Communications User’s Manual - August 1997 GFK-1084B
Section 4: Status Data
This section describes all the status data that is available to the ladder program to deter-
mine the state of the Ethernet Interface and its channels.
Types of Status Data
There are four main types of status data available to your ladder program.
1. OK Output of the COMMREQ Function Block. This output is set if the PLC CPU was
successful in transferring the COMMREQ data from the reference table memory
specified by the COMMREQ function block into the memory local to the Ethernet
Interface. This does not indicate that the Ethernet Interface has processed the
COMMREQ, only that it has been received by the Ethernet Interface.
Barring ladder programming errors, the OK and FT outputs should not both be set
in the same scan by the same COMMREQ.
2. FT Output of the COMMREQ Function Block. This output is set if there is a
programming error in the COMMREQ Function Block itself, if the rack and slot
specified in the COMMREQ Task parameter is not configured to contain an Ethernet
Interface, or if the data block length specified in the Command Block is out of range.
This output also may indicate that no more COMMREQ functions can be initiated in
the ladder program until the Ethernet Interface has time to process some of the
pending COMMREQ functions.
If the FT Output is set, the CPU does not transfer the Command Block to the
Ethernet Interface. In this case, the other status indicators are not updated for this
COMMREQ.
3. Status Bits. The status bits are updated in the CPU once each PLC scan by the
Ethernet Interface. These bits are generally used to prevent initiation of a
COMMREQ function when certain errors occur or to signal a problem on an
established channel. The status bits include the LAN Interface Status bits and the
Channel Status bits. The starting location of these bits is user-configurable. See
Chapter 2 for more information.
The LAN Interface Status bits monitor the health of the Ethernet Interface itself such
as the LAN Interface OK bit and the AAUI Fuse Blown bit. The Channel Status bits
monitor the health and progress of a channel established using the Establish Read/
Write Channel Commands.
4. Communications Status Words. There are two types of words that provide detailed
information: The COMMREQ Status word (CRS word) and the Detailed Channel
Status words (DCS words). The communications status words are not updated in
the CPU each scan as are the status bits. They are generally used to determine the
cause of a communications error after the COMMREQ function is initiated. The
cause is reported in the form of an error code described later in this section.