IDL 101
COMMUNICATION
HB_IDL101_E_V222.doc
77
Gantner Instruments Test & Measurement GmbH
10.4.2. Telegram Format
ADR
FNR
function parameters / data
CRC
request telegram
idle-interval
> 3,5 CT
1 byte 1 byte
n byte
2 byte
ADR
FNR
function parameters / data
CRC
response telegram
idle-interval
> 3,5 CT
1 byte 1 byte
n byte
2 byte
The request and response telegrams in the RTU-mode used by the data loggers are starting with an idle-interval of at
least 3.5 character lengths. Most simple this will be performed by waiting for at least 4 character-times after receiving
the last character of a telegram. The telegrams have no Start-Delimiter and no End-Delimiter too. The first field after
that idle-interval is the ISM-Address (ADR) followed by the function number (FNR) and the function parameters or data
respectively. At the end the telegrams contain a check sum (CRC) with the length of 16 bits. The check sum is
calculated from the whole telegram without the CRC itself. The CRC-polynomial is: u
15
+ u
13
+ 1. The start value is
hex
FFFF.
10.4.3. Instruction Set
With the MODBUS-protocol the data are read and written via register accesses. The following register accesses are
defined for the communication with the sensor modules:
function number
function
03 hex
read holding register (read/write register)
04 hex
read input register (read only register)
06 hex
preset single register
08 hex
Diagnostic
10 hex
preset multiple register
Table 10.15 MODBUS commands supported by the IDL 101