Atmel Micro does not load EEPROM data

[rayhall]

Hello,

I am using the micro-USB with a controller that uses the Atmel Mega2561. If I have the USB cable plugged into the PC and the micro-USB before I power the controller, the EEPROM data is not loaded into the Mega2561.

If the controller is power first I do not have this problem. I have the Tx and Rx on the mirco-USB and Mega2561 directly connected. As far as transferring data in both directions it works perfectly.

My question is should I have some component in the Tx and Rx lines. Or is there something else I should be doing to stop this.

Ray Hall.

[Atilla]

Ray,

How have you got it setup? Are you powering the controller via the uUSB or a separate supply? Which micro-USB module is it...uUSB, uUSB-MB5, uUSB-CE5 ? If you are powering up your target app via the micro-USB are you using the 5V or the 3.3V supply? Please supply more detail of your configuration.

[rayhall]

I am using the µUSB

The controller is powered by its own internal power supply. The 5volt and 3.3 volt supply on the micro-USB are not used or connected in any way. Only connections are Tx, Rx and Gnd.

Ray.

[smcmanus]

rayhall,

You've probably already done this, but two things that I tend to look for when I'm having trouble interfacing to a uController are:

1. Are the Grounds on the uUSB and the host power supply tied together?

2. Are you using pullup resistors (I normally use 10K) on the Rx & Tx lines. Some hosts don't like their Rx lines to "float" during power up. It's usually more important to have the pullup on the host Rx line.

Good luck,

Steve

[rayhall]

Steve,

I connected a 10k resistor from the uUSB 5v supply pin to the Tx pin (Rx on Mega2561) and it solved the problem.

Thank you very much.

Ray