ProSoft Technology MVI46-MCM - Manual (Page 66)

Reference MVI46-MCM ♦ SLC Platform
User Manual Modbus Communication Module
Page 66 of 108 ProSoft Technology, Inc.
March 29, 2011
Slave Status Blocks (3000 to 3003 or 3100 to 3103)
Slave status data sends status information of each slave device on a master port.
Slaves attached to the master port can have one of the following states:
0 The slave is inactive and not defined in the command list for the master port.
1 The slave is actively being polled or controlled by the master port.
2 The master port has failed to communicate with the slave device. Communications
with the slave is suspended for a user defined period based on the scanning of the
command list.
3 Communications with the slave has been disabled by the ladder logic. No
communication will occur with the slave until this state is cleared by the ladder logic.
Slaves are defined to the system when the module initializes the master
command list. Each slave defined will be set to a state of one in this initial step. If
the master port fails to communicate with a slave device (retry count expired on a
command), the master will set the state of the slave to a value of 2 in the status
table. This suspends communication with the slave device for a user specified
scan count (Error Delay Counter value in the module configuration for each port).
Each time a command in the list is scanned that has the address of a suspended
slave, the delay counter value will be decremented. When the value reaches
zero, the slave state will be set to one. This will enable polling of the slave.
In order to read the slave status table, ladder logic must be written and the slave
status data must be located in the user data area. The module will constantly
update the user defined data area with the slave data for each Modbus
Master/Slave master port. This data can be transferred to a user-defined file in
the processor using the COP instruction.
Slave status blocks send status information of each slave device on a master
port. Slaves attached to the master port can have one of the following states:
0 The slave is inactive and not defined in the command list for the master port.
1 The slave is actively being polled or controlled by the master port. This does not
indicate that the slave has responded to this message.
2 The master port has failed to communicate with the slave device. Communications
with the slave is suspended for a user defined period based on the scanning of the
command list.
3 Communications with the slave has been disabled by the ladder logic. No
communication will occur with the slave until this state is cleared by the ladder
logic.