Gantner IDL 101 - Telegram Format

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