I would like some help with identifying what is required to set up a two way communications link with my environmental probe that uses RS 485 to a logger that uses MODBUS.

 

Just because your instrument has RS485 doesn't mean it understands Modbus. It's entirely possible it's looking for some kind of custom, manufacturer specific hex or ASCII comm protocol.

You have to check its documentation to see if it will work as a Modbus slave. If so, that documentation may also explain the register layout (what registers are available to read/write, what parameter is at which register, and the encoding format). Or the docs may say that it does Modbus but not cover those topics in which case you'll have to contact the manufacturer and get that information.

You can't make the device talk Modbus unless it was designed to do so in the first place, and your question is far too short on specifics to enable anyone here to help you, especially since you should just be asking the instrument manufacturer anyway.

 

RS485 is a hardware design. MODBUS is a software messaging protocol. They are in no way the same thing.

MODBUS *may* use the RS485 hardware. You will need to read the manuals for your instrument to know if it supports Modbus over it's RS485 port.

Similarly, your logger uses Modbus messaging but knows nothing about how the messages from your instrument are formatted. Again, you need to consult the relevant manuals for both the logger and the instrument.

We can't answer your question from the information you have posted.

Rob
www[.]lymac.co.nz

 

1) If your probe can talk Modbus, the documentation will say "Modbus". If it doesn't say "Modbus", there's no Modbus.

2) Modbus is master/slave protocol.

If your instrument does talk Modbus (questionable at this juncture) it would be a Modbus slave.

To make Modbus work, your data logger would have to be a Modbus master. That is a low probability situation.

Data loggers typically collect analog and/or discrete data and make it available as a Modbus slave. One clue that a device is a Modbus slave is a register or address table/list/map. Only a slave has such.

A Modbus slave cannot talk to another Modbus slave.

 

Hello,

You need uC with 2 serial ports. At one port you must read data from your device and put it to the modbus registers. At second port you need implement modbus slave.

Regards,
Andrzej
www.modbus.pl