Monitoring Ethernet Global Data Exchange Status - GE RX3i User Manual

Chapter 5. Ethernet Global Data
Modifying Exchange Variables on Targets that use EGD Commands
PACSystems targets can service EGD commands from other devices. Some commands read or write an
exchange based solely on an offset into that exchange. If EGD signatures are not used, the exchange offset
and length requested are validated against the length of the exchange. Without EGD signatures, the definition
of the exchange can be changed entirely by an RMS and the EGD command would be serviced as long as the
offset and length in the command are valid. For this reason, caution should be used when modifying EGD
exchanges on a target that services EGD commands. Adding variables to the end of such exchanges would not
cause a problem, but modifying or deleting variables should only be done with caution.
PACSystems targets can also be EGD command clients. EGD commands can be sent to other devices via
COMMREQs in user logic. If EGD will be modified using RMS, the exchange signature should be set to the
signature value of the device that will service the command. Do not set the signature value to zero, this
effectively disables signature checking.

Monitoring Ethernet Global Data Exchange Status

5.7
The Exchange Status word is used to store status information about an EGD exchange. A unique Exchange
Status word location must be is configured for each exchange.
The PLC writes status codes into the Exchange Status word whenever an exchange is transferred or a
consumer timeout occurs
The Exchange Status word is typically set to 1, indicating that data transfer occurred successfully. The
application program can monitor for error conditions reported in the Exchange Status word by setting it to 0
once a non-zero value is written to it. In all cases, if the least significant bit of the exchange status is set to a 1,
then data was transferred successfully. Status values other than 1 with the least significant bit set (e.g. 3, 5 and
7) give information about the data that was transferred, the producer or the network that are noteworthy in the
application.
The program should also monitor the "LAN Interface OK" Status bit (see Chapter 12, Diagnostics) for each of the
Ethernet Interfaces performing EGD. The Exchange Status word is invalid if the bit is 0.
Note that when an EGD exchange message received from the network contains an invalid Protocol Version
Number, the Ethernet Interface cannot decode the message in order to identify the exchange. In this case, the
Exchange Status Word cannot be updated.
92 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q