Advice on a simple setup

[demestav]

Hey guys,

So I have 2 devices as shown in the figure that communicate with serial. I need my setup to have two operations
1) PIC turned on to process data before forwarding it
2) PIC turned off, data are passed directly from device 1 -> device 2 and the opposite

So I am thinking of having a switch to connect the lines as shown.

Do you think the PIC pins will cause any trouble in mode 2? Essentially Device 1' TX will be connected to UART2 TX pin and Device 2' TX connected to UART1 TX.

What is your opinion?

Thank you.

 

[Ian Rogers]

Why do you need an external switching mechanism.. Put a button on some port and when switched transparently transfer from uart1 (rx) to the other uart (tx)

 

[Pommie]

I think you will have a problem powering down the PIC. When a voltage is applied to any pin it powers the chip via the protection diodes. You may be able to use resistors to limit the current and a lower resistor across the supply pins to fix the problem.

Mike.

 

[demestav]

Why do you need an external switching mechanism.. Put a button on some port and when switched transparently transfer from uart1 (rx) to the other uart (tx)

I want to be able to take the PIC completely out of the picture for power saving and debugging reasons.

I think you will have a problem powering down the PIC. When a voltage is applied to any pin it powers the chip via the protection diodes. You may be able to use resistors to limit the current and a lower resistor across the supply pins to fix the problem.

Mike.

Hmm thanks Mike. What do you think about adding schottky diodes on the two TX lines of the PIC?

Thanks.

 

[Pommie]

Diodes won't help as they will still power the chip. Some 2kΩ resistors on all 4 pic pins and a 330Ω across the supply pins may work. Also make sure the brown out reset is enabled.

Mike.