Differences Between Series 90 And Pacsystems Modbus/Tcp Channels - GE RX3i User Manual

Differences between Series 90 and PACSystems Modbus/TCP
9.6
Channels
This section lists the known differences between the Series 90 implementation of Modbus/TCP Channels and
the PACSystems implementation.
1. On the 90-30 CMM321 if a Modbus error response is received for a Modbus/TCP channel, the Ethernet
interface closes the TCP connection and updates the CRSW with an appropriate error code. For
PACSystems Ethernet, the Modbus error response results in an updated CRSW with an appropriate error
code but the TCP connection is NOT closed.
2. A CRSW of 0x8390 (Invalid Server Memory Type) is returned when an invalid Modbus Function code is
specified for the CMM321. For PACSystems Ethernet, an improved CRSW of 0xB690 (Invalid/Unsupported
Modbus Function Code) is returned.
3. The TCP connect timeout (i.e. the amount of time to wait for the Remote server or Gateway to establish a
TCP connection with a Modbus/TCP Channel) is 90 seconds on the Series 90 and 75 seconds on
PACSystems. An error is returned in the CRSW for the Open Modbus/TCP Connection COMMREQ when this
timeout occurs.
4. The station manager command "stat m" on the Series 90 results in displaying "Closed" for specific Closed
channels while PACSystems Modbus/TCP Channels results in displaying nothing for a specific Closed
channel.
5. When sending a Close Modbus/TCP Connection COMMREQ, the PACSystems Modbus/TCP Client will return
a success CRSW (0x0001) while the CMM321 module returns an error CRSW.
6. The rules for Endian conversion when transferring between Word and Bit types of memory are different in
order to make these types of conversions consistent.
CMM321 Modbus Client Endian Conversion Example
For example, depending on the direction of the transfer, the end-to-end values result in bytes being swapped
for CMM321 Modbus Client. This can be seen in the example table below.
Memory
Location / Memory value
Type example
%M16-%M1 =
Client Bit
0x4321
%M16-%M1 =
Server Bit
0x4321
Client Word %R1 = 0x4321
Server
%R1 = 0x4321
Word
GFK-2224Q
Memory
Transfer Location /
Direction Type
Server Word

Client Word

Server Bit

Client Bit

January 2017
Chapter 9. Modbus/TCP Client
Resulting Value After
Transfer
%R1 = 0x4321
%R1 = 0x2143
%M16-%M1 = 0x4321
%M16-%M1 = 0x2143
Notes
End-to-end bytes
un-swapped
End-to-end bytes
swapped
End-to-end bytes
un-swapped
End-to-end bytes
swapped
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