Modbus.Modbus access to the Target

Product : ISaGRAF V3

Date : 6-March-1996

File : Modbus.Modbus access to the Target.htm

Subject : Modbus access from a supervisor to the ISaGRAF target

Keywords: Modbus - supervisor - SCADA - Network address

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- In the ISaGRAF application, specify for each variable to be spied

by the supervisor, the Modbus address in the field 'Network address'

in the dictionary.

- In the supervisor, you must have the same variables with the

corresponding addresses.

- The Modbus slave number of the ISaGRAF target can be specified

by the '-s' option:

isa -s=slave_number -t=com1

- The supervisor has to connect to this slave number

Limitations:

With Modbus, only read/write a bit, or read/write a word

possibilities are given.

This corresponds to the ISaGRAF variables:

boolean and integer analog (16 less significant bits)

In Modbus to make these reading and writing you use

function codes,

the only codes implemented in ISaGRAF are:

1: read N bits

3: read N words

5: write 1 bit

6: write 1 word

16: write N words

Please consult the 'Target User's Guide' for more information

about Modbus capabilities and Modbus frames.

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