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ADuC 7061 weird power on behavior

Question asked by ThorMJ on Apr 2, 2013
Latest reply on Apr 29, 2013 by ThorMJ

I'm scratching my head with this one...  On my custom board, using the Plug-Of-Nails JTAG adapter, it only works from power on if the programmer is attached to the board, but disconnected from the PC.  When I apply power, it launches and runs correctly.


If I have the programmer attached to the PC -but not supplying power-,  a strobe of the reset line must be performed for the uC to start up.

If I have the programmer attached, the POR executes correctly when I apply power from the programmer.

If I don't have the programmer attached, even strobing the reset does nothing until the programmer is attached. 


Main power comes from a 5V regulator, followed by a 3.3V LDO (JTAG & Peripherals) in parallel with a 2.5V LDO (Vcore).

If the programmer is supplying power, the 5V comes from the JTAG interface and runs to the other to regulators.


I have 100k pullups to 3.3V on all my JTAG lines...

Reset was bare to the switch, but I added a 1K pullup - no change.


Anybod have any ideas to help me direct my scope probe?


As an aside, why isn't the reset line run to the JTAG port?  I've had some test boards where I created a tight loop and had to use the RST->BMI to regain access to the board; if the RST line went to JTAG, it wouldn't have needed handholding like that.