mc912d60a reset problem

[sprince]

I'm having a problem with the reset of my d60a circuit from time to time.  Once in a while, the reset won't work and my program goes into never-never land.  It sometimes returns after 4 seconds, making me believe the watchdog timer times out eventually, and resets the chip.  Since I set the timer to time out at .25 seconds in code, I know it is never getting to this point in the program.  Seems to me I have a "runaway code" problem due to the reset circuit, that cannot be changed on our circuit (encapsulated).

Is there any code that could be placed in unused memory locations that would "force"  a reset?

Stewart Prince

[sprince]

So....I guess there's no fix to my problem, because the boards are already encapsulated.  Do the "C" versions (mcs912c32) have the same problem??  I am using the standard 34064 reset ic provided by onsemi to reset/monitor the device.  Is there another one offered with a longer delay?

Thanks

[kef]

Why no fix, you should just replace your MC34064 with something like Microchip MCP120 or MCP130. I believe that if not MCP120, then some other part could replace your MC34064 without any PCB mods. You didn't say what package is your MC34064 so I can't suggest exact part number.

MC9S12C32 doesn't have such problem. More over using C32 you don't need any reset chip, because S12C family have built in Low Voltage Reset (LVR) circuit.

[kef]

Try changing your reset chip to reset with delay reset chip. D60A is using Collpits oscilator, which starts up slowly, probably much slower then your power supply rise time. And internal PON reset may be released too early, when clock is not yet stable, and that may cause runaway. So chceck with scope how long does your oscilator start up and use suitable reset chip with reset release delayed.