MC34709 GLBRST pin working inconsistantly

[paulweichelt]

We have a reset button connected to the GLBRST on our

MC34709. The reset button is working intermittently/inconsistently.

We have the register set to 4 second hold to initiate a reset. At

various times we get the following results:

1. Hold the button for 4 seconds and the unit stays
   in reset until the button is released. (This is the operation we expect.)
2. Hold the button for 4 seconds and the unit
   resets without releasing the button.
3. Hold the button for 4 seconds and the unit won’t
   come out of reset until the power is cycled. All voltages stay low and the
   atlas never powers up or releases reset.

Some boards always exhibit behavior 3 above. Some boards exhibit behavior

1 or 2 above until they warm up (core temp of 120-130F) and then they start

exhibiting 3.

[art]

What is the setting of GLBRSTTMR[1:0] bits in your case? Does the button simply pull the GLBRST pin low? Isn't there any external pullup/signal source? Also, please check the MC34709 Errata document, it is available on the part's Documentation web page:

http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC34709&fpsp=1&tab=Documentation_Tab

Check whether the issue is the possible effect of the part's silicon errata.

Have a great day,
Artur

[paulweichelt]

The GLBRSTTMR[1:0] is set to 01 to give us a 4 sec button hold time. The reset button pulls the GLBRST to GND. There is no external pullup, just the internal pullup. I have scoped the GLBRST line and it seems to be functioning normally. The reset button is pulling it down and the internal resistor is pulling it back up. I have not seen any bouncing. We have tried it both with and without a capacitor on the GLBRST line. It seems to work slightly better with no capacitor, but still fails intermittently. I have read the errata, but not of the errata items seemed to apply to this problem.