89C668 reluctant to run user code

[david fussell]

Hi,

I'm happy to say that I can reliably enter ISP mode, and can re-program the '668 device repeatedly with no problem, so please excuse the slightly off topic subject, but I was hoping someone may have experienced this before:

The problem I have is that it's a bit variable as to what is happening upon non-ISP mode startup- The user code (currently just flashing led's ) sometimes runs straight away, but usually there's no activity for a minute or so before the user code runs.

I'm suspicious that the PC may not be getting set to 0x0000 upon power up, but asserting a reset (RC) during this minute of 'idle' time has no apparent effect. During execution of user code however, the reset works fine.

...all supplies and signals appear clean.

Any suggestions?

David

[Rons]

Hi,
     I've been using the 89c668 for a while now. If I were you I would disable
interrupts to start with.  Try to toggle a port pin low and look at it with a scope,forget about your led's for now. Sounds like you are almost there.