I'm using a non-PIC microprocessor with no reset pin and a totally internal
power on reset and anti-brownout capability. Allegedly.
No confirmation or denial will be given to people guessing the processor
type and I'd rather people didn't guess in public at this stage :-).

The spec sheet states a Vdd voltage level below which the processor should
be in reset mode and above which it should be operational. No requirements
are placed on the rise time of Vdd to meet reset conditions.

In practice my mileage may and does vary.

Depending on batch and temperature code SOME of the processors do not reset
cleanly if the Vdd is raised slowly. It happens that slow and variable Vdd
rise times are an essential 'feature" of this environment unless I redesign
the circuit substantially. This problem varies with processor batch and has
only been identified recently.

All processors, whether "faulty" or OK, have their clocks start at about 2.2
volts and the internal reset circuit lets them start working at about 2.8
volts. The part is specced to run fro 3 to 5.5 volts. I am running a 5v
supply. Good processors and faulty processors can NOT be distinguished by
their clock starting action. This is NOT a clock starting
problem.

The requirement of coming out of reset cleanly with no limitation on Vdd
rise time is a strenuous one BUT I would think an essential one for a
processor with no reset line.


QUESTIONS:

1.    Is anyone else using a reset-line-less processor and does it always
work?

2.    What do people think about a processor failing in these admittedly
somewhat unusual circumstances.

3.    Any thoughts re work arounds. Fairly obviously I need to either "fix"
the processor or decrease the Vdd rise time. "Select on test" of good
processors is not an economically viable option. Fixing the rise time is
annoying as I have no control on the rise time of the input to the 5v
regulator. Adding extra components is an undesirable requirement at this
stage :-(.

4.    What should i say / would you say to the manufacturer (who doesn't
seem to yet really appreciate the problem as few if any other customers
would be troubled by it).

5.    What would you think of a processor that behaved like this?
I assume that in more normal circuits some of these will sometimes cause
problems. These problems would be hard to track down and there cause may
remain a mystery indefinitely.


TIA



      Russell McMahon
_____________________________

What can one man* do?
Donate food daily free !!! -  http://www.thehungersite.com/
Donate Vitamin A!  http://www.thechildsurvivalsite.com/
www.rawa.com  - one perspective on Afghanistan
www.changingourworld.com    www.easttimor.com   www.sudan.com

(* - or woman, child or internet enabled intelligent entity :-))

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads