PLCs that support networking communication capabilities over Modbus Plus and Ethernet have a special MSTR (master) EFB with which nodes on the network can initiate message transactions.

The L9_MSTR EFB allows you to initiate one of different possible network communication operations over the network. Each operation is designated by a code. Certain MSTR operations are supported on some networks and not on others.

The L9_MSTR function block is supported on various hardware platforms.

L9_MSTR has two control inputs. ENABLE activates the EFB when it is ON. TERM terminates the active operation when it is ON.

L9_MSTR can produce three possible outputs. OUT echoes the state of ENABLE- i.e., it goes ON while the EFB is active. ERR echoes the state of TERM-i.e., it goes ON if the MSTR operation is terminated prior to completion. SUCCESS goes ON when a MSTR operation has been completed successfully.

For further information refer to chapter MBP_MSTR: Modbus Plus Master.