We are presently installing precip controllers that communicate on modbus lite. We want to access information on the DCS from the modbus lite network.

Where can we get more information on modbus lite? Is this protocol able to talk to the Honeywell TDC2000 system?

Regars,
Sagren

 

There is no protocol called "modbus lite".

The standard protocal is just Modbus. Other variations are Modbus Plus and Modbus TCP.

I have customers that have been using Honeywell TDC systems with Modbus protocol for many years.

 

Modbus "lite"? Sounds like a name given to a specific application.

Remember, Modbus is a protocol. You don't buy Modbus off the shelf. It is written or applied to a communications task. Modsoft, Proworx and Concept use Modbus protocol to communicate with the PLC. HMI and DCS devices also use Modbus protocol to communicate.

In your case, from the term "lite", I would assume that the applications programmer implemented only a few of the available commands. May only have included read and write registers and not read and write coils. Or something like that.

DSC vendors typically have full featured Modbus communications capabilities. Some have Modbus Plus and Modbus TCP/IP.

 

MODBUS lite (we used to call it Mini-MODBUS) is probably a subset of only 6 commands:
Read and Write Coils
Read and Write Holding registers
Read Inputs
Read Input registers
the most "popular" - out of the many commands available in this protocol.
Everything else is the same.
Meir

 

Sorry, never heard of "Modbus/Lite" - I'd wager a guess that it is a simple subset of Modbus - maybe only function 0x03 and 0x16, maybe only Modbus/ASCII if the end device is a small CPU that has trouble with big programs or 16-bit math.

You'll need to read the vendor docs to see what they are calling Modbus lite.

best regards
- LynnL, www.digi.com