Talking Modbus to a custom build system


Thread Starter

Peter Bubik

Hello, I have a custom build hardware that communicates only in machine code via RS232. I can hook it up to a serial port of a PC an give it commands in HEX ; for example F1 80 71 will return 24 bytes descibing the status of the hardware. I need only about 25 commands - such as above - translated so that I can connect this hardware to an RTU. Is it possible to translate these commands to Modbus or DNP3.0? How much should I expect it to cost? Will I need a hardware box that will do the translation on the fly? Any idea who does that? Thanks, Peter

Carlos Araya Mackenney

Peter: I made many drivers for translate proprietary protocols to MODBUS and DNP: software solution in a PC. We developed black boxes with a CPU to make the same type of translation (MODBUS and DNP). In my opinion, you can make a MODBUS translator very fast (one week) in a PC using Visual Basic or C. If you want a DNP 3.0 translator, I think you need over 3 months if you don't have experience in this protocol. If you want to develop a black box, there are few ideas: 1. Choice a CPU with RS485 comm port. RS232 is not a good solution for automation systems. 2. If you use a RS485, remember MODBUS and DNP are addresable protocol, then you can plug many devices in the same comm channel in multidrop. Then your black box must have a way to set the unit ID or number. 3. If you design a multidrop architecture, then your black box can be more than a translator. The black box can be "reading" the unit (in propietary protocol) all the time and storing the data in local memory (like the MODBUS Memory Map). Then any polling to the black box from the computer or SCADA system id answer by the box with the data stored in. This solution is better because you are making a "little" concentrator attached to the legacy device. I hope this info will can help you. Regards, Carlos Araya Mackenney [[email protected]] Automation Manager - PLC International S.A. Phone (562) 269.8727 - Fax (562) 269.8728 Santiago, Chile
I want to have modbus device driver code in C/C++ under Linux (ASCII/RTU). Can anybody tell me where to get the source-code ?