Prosoft-technology MVI69-MCM User Manual download pdf (Page 124)

Reference MVI69-MCM ♦ CompactLogix or MicroLogix Platform

User Manual Modbus Communication Module

Page 124 of 167 ProSoft Technology, Inc.

March 22, 2011

5.5.2 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

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 (E

RROR

ELAY

OUNT

parameter in the configuration file). 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.

In order to read the slave status table, refer to the sample ladder logic. The

ladder logic must send a special block to the module to request the data. Each

port has a specific set of blocks to request the data as follows:

Block ID Description

3002 Request status for slaves 0 to 59 for Port 1

3003 Request status for slaves 60 to 119 for Port 1

3004 Request status for slaves 120 to 179 for Port 1

3005 Request status for slaves 180 to 239 for Port 1

3006 Request status for slaves 240 to 255 for Port 1

3102 Request status for slaves 0 to 59 for Port 2

3103 Request status for slaves 60 to 119 for Port 2

3104 Request status for slaves 120 to 179 for Port 2

3105 Request status for slaves 180 to 239 for Port 2

3106 Request status for slaves 240 to 255 for Port 2

The following topics describe the format of these blocks:

Write Block - Request Slave Status

Offset Description Length (words)

0 3002 to 3006 or 3102 to 3106 1

1 to n

Spare

n=60, 120, or 240 depending on the Block Transfer Size parameter (refer to the configuration file).

The module will recognize the request by receiving the special write block code

and respond with a read block with the following format:

1 2 ... 119 120 121 122 123 124 125 126 127 128 129 ... 166 167

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