Chapter 9. Modbus/TCP ClientGFK-2224Q January 2017 1719.6 Differences between Series 90 and PACSystems Modbus/TCPChannelsThis section lists the known differences between the Series 90 implementation of Modbus/TCP Channels andthe PACSystems implementation.1. On the 90-30 CMM321 if a Modbus error response is received for a Modbus/TCP channel, the Ethernetinterface closes the TCP connection and updates the CRSW with an appropriate error code. ForPACSystems Ethernet, the Modbus error response results in an updated CRSW with an appropriate errorcode but the TCP connection is NOT closed.2. A CRSW of 0x8390 (Invalid Server Memory Type) is returned when an invalid Modbus Function code isspecified for the CMM321. For PACSystems Ethernet, an improved CRSW of 0xB690 (Invalid/UnsupportedModbus 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 aTCP connection with a Modbus/TCP Channel) is 90 seconds on the Series 90 and 75 seconds onPACSystems. An error is returned in the CRSW for the Open Modbus/TCP Connection COMMREQ when thistimeout occurs.4. The station manager command “stat m” on the Series 90 results in displaying “Closed” for specific Closedchannels while PACSystems Modbus/TCP Channels results in displaying nothing for a specific Closedchannel.5. When sending a Close Modbus/TCP Connection COMMREQ, the PACSystems Modbus/TCP Client will returna 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 inorder to make these types of conversions consistent.CMM321 Modbus Client Endian Conversion ExampleFor example, depending on the direction of the transfer, the end-to-end values result in bytes being swappedfor CMM321 Modbus Client. This can be seen in the example table below.MemoryLocation /TypeMemory valueexampleTransferDirectionMemoryLocation /TypeResulting Value AfterTransfer NotesClient Bit %M16-%M1 =0x4321 Server Word %R1 = 0x4321 End-to-end bytesun-swappedServer Bit %M16-%M1 =0x4321 Client Word %R1 = 0x2143 End-to-end bytesswappedClient Word %R1 = 0x4321 Server Bit %M16-%M1 = 0x4321 End-to-end bytesun-swappedServerWord %R1 = 0x4321 Client Bit %M16-%M1 = 0x2143 End-to-end bytesswapped
