sleeping xbee and UART

Hi all

I have one xbee S1 node configured in cyclic sleep mode and a MCU conected to Din to send data. I want to shut down my MCU when xbee is sleeping but i notice that UART lines are held up. Is this normal for a sleeping node? Is there any way to disable UART when xbee is sleeping?

The UART lines will be held at their default values while the radio is in a sleep state. What you should be monitoring is the On Sleep pin from your processor and use the /CTS line to tell you when you can send and receive data.

Yes, i’m using sleep pin to monitor xbee activity, the problem is UART that is held high when xbee is sleeping. that way my MCU rx/tx lines are high and i cannot power off the MCU (i can destroy it if there are voltage on input pins when power is off).

So, my question is: is it possible to put xbee UART in low state when xbee is sleeping?

Sure you can with the PR command. Just understand that it is bad to have some lines Low on a power up state such as DI. Doing so will result in putting the radio into command mode.

Hummm… as you said, messing with pullup with PR command seems bad idea, i had to change PR bit for Di every time radio sleeps/awakes, not sure if it is going to work.
So there is no default LOW state for Di pin when radio is off (like sleep pin), right?
I can isolate Di/Dout pins from xbee to my RX/TX MCU pins with a buffer IC, i would like to avoid that but it seems the only way…

No. At 3VCMOS level, the default value for DI is High. That is to say the idle state for DI is a high state. This is per IEEE engineering standards.

Ok, thanks for the information.