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MSTR TCP 'Open Connection' Option

Goals and Symptoms

The purpose of this Resolution is to inform users of Momentum Ethernet processors of an enhancement option to the MSTR function block that allows the TCP connection to remain open.


Facts and Changes

This resolution describes how to implement the ‘Open Connection’ option for the MSTR TCP/IP block in the 984LL Exec (v.1.20 and higher) and the MSTR EFB blocks in the IEC Exec (v.1.21 and higher).

Causes and Fixes

984LL MSTR Function Block
A new feature has been added to 984LL Exec. versions 1.20 and higher where power is asserted to the bottom input of the MSTR block. Asserting this ‘go-again’ input, along with the top enable input, causes the TCP connection to remain open. Once the connection has been established, only Modbus command and response packets are transmitted onto the Ethernet. The only difference is that the repetition rate cannot be specified. It goes as fast as the scan and the target server can accommodate. No dynamic changes to the control block are accepted until the ENABLE (top) input is pulsed.

984LL Function Block Example for Open Connection operation.



IEC MSTR EFB's
A new feature has been added to IEC Exec. versions 1.21 and higher by setting a bit in the ‘Slot_ID’ of the EFB ‘TCP_IP_ADR’. Asserting this ‘go-again’ bit, along with the TCPIP operation bit causes the TCP connection to remain open. Once the connection has been established, only Modbus command and response packets are transmitted onto the Ethernet. The only difference is that the repetition rate cannot be specified. It goes as fast as the scan and the target server can accommodate.

The Slot_ID of the EFB TCP_IP_ADR has extended usage:
Bit 0 = 0 MBP operation
1 TCPIP operation

Bit 1 = 0 The TCP port will be closed after the transaction has completed (as before)
1 The TCP port will be held open

Bits 2 through 7 are reserved and must remain at 0.

Note Map_Idx = 0 for Momentum M1E Processors

IEC EFB Example for Open Connection operation:
Register 400050 = 3 hex

This feature is only useable for the following EFB’s:
CREAD_REG
CREADREG
CWRITE_REG
CWRITEREG
MBP_MSTR (needs to be always kept active: ENABLE=1)

Do NOT use this feature with the following EFB’s:
READREG
WRITEREG
READ_REG
WRITE_REG

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