35 |
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| #220
–
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RIOT Technology Corp.
Appendix D: Modbus Programming Manual
The GroPoint Lite Profiling Probe (GPLP) Modbus version uses standard Modbus RTU protocol
(RS-485). The probe can only operate as a slave device. Sensor factory default address is 01.
The sensor address can be changed via holding register 40201 (see below). Default communi-
cation settings are 19200 Baud, 8 Bits, Even Parity, one Stop Bit. Other communication parame-
ters may be selected by writing to the appropriate holding registers. See GPLP Modbus Register
Lists on the following pages for a complete list of the available Modbus registers.
•
NOTE: For more information about Modbus RTU protocol, please visit
Modbus Command Functions
Supported Function Codes/Commands
The GPLP Modbus probe supports the following subset of Modbus commands:
Function
Code
Name
Notes
Broad-
cast
03 (0x03)
Read Holding Registers
Maximum of 9 in one read
No
04 (0x04)
Read Input Registers
Moisture Values, Temperature
Sensor Values. Maximum of 9
in one read.
No
06 (0x06)
Write Single Register
Single registers only
No
08 (0x08)
Diagnostic
Supported subfunctions
[TBD]:
0 - return query data
1 - restart communications
4
–
force listen only mode
No
11 (0x0B)
Fetch Comm Event Counter
No
17 (0x11)
Report Slave ID
Returns the ASCII encoded
string
‘RIOTTECHGPLPTC
vvvSNnnnnnn’
where vvv is the firmware ver-
sion (v.v.v) and nnnnnn is the
probe serial number.
No
Unsupported Function Codes/Commands
All remaining public command function codes listed below will return an exception response
with an exception code value of 01 indicating that the command function is not supported:
01
–
Read Coils (0x01)
21
–
Write File Record (0x15)
