PLC communication by RS232


Thread Starter


I am a University student. I need to do a project using Hitachi PLC. Can someone know how to write a program for sending the data from PLC to the PC by RS232. In PC, I will receive the data by Visual Basic.
Thank you very much.
Pls reply me a.s.a.p.
Sorry, I don't understand the meaning of protocol for the PLC. Can you explain what is the protocol? And I just want to know how to write a program for sending the data to the computer in real time. Thanky you very much!

Usually when we communicate between a PLC and a PC, we use a "protocol," which is a format or language that both the PC and the PLC can speak, just like two PC's talk on a network using TCP/IP. A brief internet search for Hitachi AND PLC reveals that Hitachi supports, Profibus, Devicenet, and Fieldbus. If the PLC is capable of reading and writing Ascii strings from the R232-C port, that may prove to be the simplest solution for you. Some manufacturers also give instructions of how to format commands through the
programming port to read or write directly to the PLC memory. If you give more detail to the list of what model PLC and what special I/O modules you
have available, I or someone else will be able to give more detailed help.

Thank you
The Type of Hitachi PLC is EH-D28DTP I used.
I am using the Ladder diagram to write the program. I have tried a function called "Trans" to send the data through RS232-C directly. But I can't succeed. So can smart guys give me more detail for writing the program.
Thank you
As a test to verify your PLC can talk out of its RS232 port, try setting up Hyperterminal on a Windows PC to listen to a com port. The port settings (baud rate, # of data bits, parity, stop bits and flow control) have to be identical between the PLC and PC. Then the cable has to be wired just right. Unfortunately industrial manufacturers don't seem to like to use standard cables. You need to find out from Hitachi what the pinouts are for your port. Until all of this is just right, it will appear that nothing is happening. Once it's right, you should be able to see whatever is transmitted come up on the screen of your PC.

Try this forum at hitachi's site and you will have a better chance of finding a Hitachi expert.