RS485 Echo problem

[bozzo]

Hi everyone,

I have to PIC communicating over RS485 everything was fine
between 18F2620 and 16F628 with SN75176

But i had to change one of the PIC so i changed 16F628 to 16F690

but now i am getting on 16F690 the same data which i am sending.

what can i do any suggestions.

[bozzo]

i tried with ADM1485 it is working fine

but how can i solve it with other rs485 chips.

Thanks.

[n-squared]

The question that comes to mind is why you did NOT get an echo for the previous devices. RS-485 always returns transmitted data to receiver, unless you disable RX.
Could you post your code and schematic diagram?
_________________
Every solution has a problem.

[bozzo]

I searched this problem a little while.

First thing i found was that the voltage levels could be different;

voltage levels from different pins or device can be different (CMOS TTL ST etc.)

And on first device when i was disabling RX the time for disabling was enough but it wasn't enough for other device.

So in conclusion the code was almost the same i just changed the time between disabling TX and enabling RX.

Thanks.