[SOLVED] Problem in data reception through RS485.

[Raady Here]

PIC24F512GP806
MPLAB 8.8

Hi,

I have an application, where user will have GUI, in which he can send data in any of 24 text columns provided, and that 24 texts are transmitted through RS485 to the corresponding controller board based on the ID number given by us in the controller.

I have no problem in data reception to the controller board from GUI when I connect individually, every thing works fine, and I can cross check that received data by throwing that data on to a hyper terminal.

When I have done the same but in a set of 24 connected in series, and when I am sending data through GUI, only 12 were able to receive data and the remaining doesn't receive any thing. I have interchanged the boards and cross checked again, but first 12 connected in series are working with accuracy and remaining 12 doesn't receive.

Any guess of what could be the problem be ?

Regards,
Raady.

 

[ud23]

Please post your code or the part of code which use to communicate to the 24 set of board in series to help you better

 

[Raady Here]

thanks for your support.
replies obtained at other forum https://www.microchip.com/forums/m838732.aspx

 

[FvM]

replies obtained at other forum

A good example that shows how much essential information is missing in your initial post.

And it still does. For a serious answer about necessary or dispensable termination, one needs to know baud rate and cable length.

 

[Raady Here]

I am sending information from a software where that data is to be received on 24 boards accordingly.
connections made are in parallel. A total of 100 m to 150m wire will be used approximately. I will be using for reception alone, transmission is not used from RS485 that I use.
I have already received boards that hold a 100 ohms terminating resistor on each board. For the moment I have tested by removing the terminating resistors expect for the last and first one, and that working fine. I am using a baud rate of 9600.
I have received a suggestion that I need to add a 100 ohms as terminator at the end of wire instead on the board , since in huge production using terminating resistors in firs and last board alone might prone to human errors if the board are interchanged.

 

[FvM]

I have received a suggestion that I need to add a 100 ohms as terminator at the end of wire instead on the board , since in huge production using terminating resistors in firs and last board alone might prone to human errors if the board are interchanged.

Yes, that's the suggested standard termination. If you manage somehow to implement it this would be the best option.

9600 baud can probably run over 100 or 150 m without any termination.