M&M
R
EFRIGERATION
I
NC
. C-9
Appendix C: Software Interface Description
Preset Single Register
The Preset Single Register function code (0x06) is used to change the contents of a
single register within the M&M controller. Any register within the Control Message
and Setpoint Messages may be changed as long as the address and data are within
the valid range.
The following table is an example of the use of the Preset Single Register function
code for changing the value of the S1 Suction Pressure Control Setpoint to 0 PSIG
(14.7 PSIA) using Modbus word address 40202.
Preset Multiple Registers
The Preset Multiple Registers function code (0x10) is used to change the contents of
one or more registers within the M&M controller. Any group of registers within the
Control Message and Setpoint Messages may be changed as long as the number of
registers addressed does not extend beyond the valid range.
The following table is an example of the use of the Preset Multiple Registers function
code for changing the value of the S1 Suction Pressure Control Setpoint to 0 PSIG
(14.7 PSIA) using Modbus word address 40202 (M&M word address 201).
Error Messages
The Modbus protocol provides for the return of error codes in the event of a data error
within a correctly formatted message block. When the M&M controller detects an
error within a read or write message, the message response will contain an error
code instead of the expected data response.
The following example shows an error response to an illegal data value in a Preset
Multiple Registers command.
Unit Address 0X??
Function Code 0x06
Register Address Hi 0x00
Register Address Lo 0xC9
Preset Data Hi 0x00
Preset Data Lo 0x93
CRC-16 0x??
Unit Address 0X??
Function Code 0x10
Starting Address Hi 0x00
Starting Address Lo 0xC9
No. of Registers Hi 0x00
No. of Registers Lo 0x01
Byte Count 0x02
Data 1 Hi 0x00
Data 1 Lo 0x93
CRC-16 0x??
To Next Page
Loading...
Need help?
General