ProSoft Technology MVI71-MCM - Manual (Page 67)

Reference MVI71-MCM ♦ PLC Platform
Modbus Communication Module
ProSoft Technology, Inc. Page 67 of 111
December 28, 2007
5.2.8 Slave Status Blocks
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:
State Description
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 and
communications is successful.
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. 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.
Block ID Description
3002 Request for slave status values for Port 1 slaves 0 to 59
3003 Request for slave status values for Port 1 slaves 60 to 119
3004 Request for slave status values for Port 1 slaves 120 to 179
3005 Request for slave status values for Port 1 slaves 180 to 239
3006 Request for slave status values for Port 1 slaves 240 to 255
3102 Request for slave status values for Port 2 slaves 0 to 59
3103 Request for slave status values for Port 2 slaves 60 to 119
3104 Request for slave status values for Port 2 slaves 120 to 179
3105 Request for slave status values for Port 2 slaves 180 to 239
3106 Request for slave status values for Port 2 slaves 240 to 255
The format of these blocks is as shown in the following table:
Offset Description Length
0 3002 to 3006 or 3102 to 3106 1
1 to 63 Spare 63
The module will recognize the request by receiving the special write block code
and respond with a read block with the following format:
Offset Description Length
0 3002 to 3006 or 3102 to 3106 1
1 Write Block ID 1
2 to 61 Slave Poll Data Status 60
62 to 63 Spare 2