Problem In Interfacing The AT89C51 With VB 6.0

HEllo Friends !

I am working on the project in which we are working on the Microcontroller Based Distributive Control System..

In this our three Control systems are connected to the Microcontrollers and they are getting the data from the sensors continously.

In this our PC is working as a master and we are working on the Visual Basic 6.0.
In VB we are getting the data from each MCU slave. This process is doing continously.

The Problem is :::::

When we sonnect the each slave separately then it works perfectly and we are getting the correct data. But when we connect the three salves at a time then only single slave work properly and other two slaves are unable to send the data to computer.

I have connect the Serial port to three ports by connecting the three DB9connectors parallel to it and this cable I have checked, it is working perfect.

Now please tell me that what will be the problem in this progame.

Is it due to the Buffering from the SERIAL PORT, so that it is not getting the data from the slaves ??????

If anyone have any idea then please tell me.

Thanks in advance.

Take Care

Zeeshan Shareef

First you should sort out hardware conflict: you can't connect 3 TX pins in parallel, unles you use multidrop device such as MAX3323 .. see attached picture ..
More details at:
**broken link removed**
After this is sorted out you can attempt to check out your software, but bear in mind, that only one slave should "talk" to the Master at a time ..

Regards,
IanP

The MAX3323 does the same thing as MAX232 but, if required, it can be put into high impedance state and you have to use it instead of MAX232 ..

Regards,
IanP

Assalamo Allykum
hi shani i work in the same project that you mention i like to help me how the master computer know each address of the slave connected and i have a lot of information that my help you please replay on this e_mail
engg_msc@yahoo.com

Why not use RS485 ?

vsmGuy said:

Why not use RS485 ?

Click to expand...

Now that's a much better suggestion. RS232 is very distance limited and was never designed for multidrop communications.

Uh hu.. but writing the the protocols are not that much funn ;-)

Hint : SMBus

plz use following two website for vb interfacing

www.8051projects.com
www.8052.com