Rockwell Automation AADvance Controller Configuration Guide - Manual (Page 211)

 
Document: 553633
ICSTT-RM405f-EN-P
Issue 07
9-25
Controlling a Modbus Master Object
Every Modbus master object has a pair of registers (holding registers), which allow the
application to control the object, and to retrieve status information. The registers are
a 'control register' and a 'status register'. Each register is located at a unique address
— the Control Variable Address and the Status Variable Address.
The use of the registers is optional. If you want to use a register, you have to declare a
variable for it in the application Dictionary and also specify the address in the holding
register map.
An application can use the control register to control a specific master. If you do not
specify a control variable address, then the master is enabled automatically when the
controller is started. The variable in the application Dictionary has the functions listed
in the table.
Table 26: Modbus Master Control Register
Value Meaning Description
0 Inactive Disables the Modbus master
The link is inactive, no communications activity
All connected slaves set inactive
1 Standby Forces the Modbus master to operate in its standby mode
Link is active but no data is being transferred
2 Active Forces the Modbus master to operate in its active mode
Link is active and transferring data
Note: If the application sets the control register to any other value, the Modbus
master is disabled.
The status register is an unsigned integer value (UINT) that is returned by the
Modbus driver to allow the application to monitor and act on faults. If you do not
specify a status register address, then the master does not report its status information
to the application. The variable in the application Dictionary has the values listed in
the table.
Table 27: Modbus Master Status Register
Value Meaning Description
0 Healthy The Modbus master is operating normally
Link is active, no errors reported
1 Initializing The Modbus master is initializing
2 Error The Modbus master has encountered an error and is disabled
Unable to establish link