Hi
I designed an SH3-7709 (80MHz) based industrial controller about 2 years ago, which has been used in a number of applications. This has worked fine after initial debugging and board validation etc. and has been in production now for over 18 months.
Recently the contract assembly house was changed to get better quality and value, as the manufacturing volumes are beginning to grow.
I have just received the first of the production boards from this new supplier and I have a problem!
The CPU (HD6417709F80) doesn't function after power-on-reset; i.e the
10MHz crystal feeding the internal oscillator doesn't start at switch-on. Only when I inject a manual reset into the cpu that it starts to oscillate!I have checked all the component specifications etc and I don't see any difference between the old board and the newly built one. The reset circuit (using MAX811/5v and MAX6361/3v3 in tandem) generates a clean POR after switch-on. The load capacitors for the crystal are correct value (after all they function after a manual reset!). All the other components for the PLL 1 & 2, and all the necessary pull-ups and mode switches for the cpu are correct and as before.
There are only two unrelated and minor changes with the board artwork; the board manufacturing spec is the same (4layers with ground and power planes, 1oz copper, gold-flash etc).
The finished board from the new supplier looks great; it is very clean and well assembled. Compared to this I still have my very first hand-assembled prototype board with a bird's nest of cuts and links which still works fine.
After the power-on, and me providing a manual reset the board and all the software works fine as per the designed functionality.
I am totally stumped at the moment! What has gone wrong? I need this board to work in the machines at power-on without fail.
I am beginning to doubt my sanity or that something has changed in the
7709 that nobody has told me about. Latest data from Renesas now refers to 7709S and the hardware manual I downloaded today still gives identical info as the 7709/80MHz regarding the oscillator/PLLs and reset conditions etc.Can you please help? Or do you know someone who can?
Thanks in anticipation,
Khalid