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Modbus Read, Write and Override Parameters plus Exception Codes
194 UDC2500 Universal Digital Controller Product Manual 4/07
10.6 Using a Computer Setpoint (Overriding Controller Setpoint)
Overview
You can use a setpoint generated from the computer to override the setpoint being used
by the controller. The value generated by the computer will have ratio and bias applied
by the controller.
Register Addresses
Use the identifying code in Table 10-7 to enter the computer setpoint.
Table 10-7 Computer Setpoint Selection
Parameter
Description
Register
Address
Data
Type
Access Data Range or
Enumerated Selection
Hex Decimal
Computer
Setpoint
007D 125 FP R/W Value from computer with
Ratio and Bias applied by
the controller. Within the
Setpoint Range Limits in
Engineering Units or
Percent.
Shed
The computer setpoint override will continue until SHED from communications occurs
or the controller is placed into monitor mode through communications. Doing periodic
SLAVE READS within the shed time will allow the override to continue until
communication is stopped and shed time elapses. Does not apply to IR communications.
ATTENTION
0 Shed (code 79) allows the override to continue indefinitely or until the reset shed timer
register address 1B90 is written using function code 6 or register address 7F using
function code 21. Any data value can be written because it is ignored.
When SP is overridden, the upper display becomes “COM” momentarily, and the lower
display shows the CSP value as CSXXXX.
Table 10-7.1 Shed Timer Reset
Parameter
Description
Register
Address
Data
Type
Access Data Range or
Enumerated Selection
Hex Decimal
Shed Timer
Reset
7F 127 FP W Exit Slave Mode
IR Only