Gantner IDL 101 - MODBUS-Protocol

IDL 101
COMMUNICATION
76
HB_IDL101_E_V222.doc
Gantner Instruments Test & Measurement GmbH
10.4. MODBUS-Protocol
10.4.1. Transmission Sequence
In the MODBUS-protocol data are transmitted from and to the data logger by means of the following sequence:
DA
.. ..
CRC DA .. .. .. .. .. .. .. .. CRC
request telegram response telegram
T
1
request telegram
T
2 T3
DA
.. ..
CRC
T
1
: time between two characters
T
2
: time between request-telegram and corresponding response-telegram
T
3
: time between response-telegram and next request-telegram
You will find the minimum and maximum appearing values for T
1
, T
2
and T
3
and the adjustment range in the following
table 10.14.
protocol baud rate T
1min
T
1max
T
2min
T
2max
T
3min
T
3max
adjustable no no yes no no yes
M
O
D
B
U
S
2,400 bps
4,800 bps
9,600 bps
19,200 bps
38,400 bps
0 150 ms 1 ms 80 ms 3.5 CT arbitrary
Table 10.14 Values and adjustment range for the times T
1
, T
2
and T
3
(CT: character time: 1 CT = character length [bit] / baud rate [bps])
The values for T
2min
and T
3max
and the behavior of the data logger if the time T
3max
is exceeded (communication timeout,
see also chapter 6.8, error handling) can be adjusted by means of the
Configuration Software ICP 100 . The default
values for the time T
2min
is 1 ms and for the time T
3max
3.5 CT.