Product : ISaGRAF 3.3

Date    : 06-April-2000

File    : using TSTCOMRQ Modbus master.htm

Subject : How to use tstcomRQ Modbus Master with ISaGRAF 3.3 kernel

Keywords: Modbus master- Client - TSTCOMRQ


1) Create an ISaGRAF 3 application.

When declaring variables in dictionary, assign Modbus addresses (network address) to each of them.

(example application TST_MDB).

Compile and download TIC code to your PLC.

2) Open a DOS session and enter following command

MODE COM<n>: 19200,N,8,1

Where <n> is serial port number you want to use.

(if you are under NT, DO NOT use "isamod.exe" we provide, this executable

does not succeed to set com.parameters on NT)

3) Enter following command in DOS session:


Where <n> is serial port number you want to use.


4)Read chapter "C.8 Modbus Link" of "ISaGRAF 3.3 User's Guide" manual.

and look at request structures.

As shown in tstcomRQ interface:

- size of a request has to be entered in Decimal.

- bytes you enter have to be entered in hexadecimal.


5) look at the bitmap below, it shows what you could get on screen when

using tstcomrq if application TST_MDB is running in your PLC.

Application and tstcomrq.exe are found in ModbusMasterTstComRq folder with this FAQ,

or ask to


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