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'SX Power On Reset problem'
1999\02\15@061843 by ruben

Hello everybody

I'm having problems with getting a SX28AC chip to
reset at power on.

When the power in my circuit has been turned off for
long enough (a couple of seconds) the SX won't reset
on the next power on. Instead it sets or quickly pulses
some of my port pins after abt 65 ms. If I now manualy
reset it by bringing the *MCLR pin low and high again
it allways resets as it should. I have also tried to
hold *MCLR low for a couple of seconds when power is
switched on and then returning it high. This won't reset
the chip either, but the next toggle of the *MCLR pin will.

I have tried using both the internal brownout detector and
an external DS1233 reset chip with the same result.

The risetime of the 5V to the chip is less than 10 ms at
power up (and it looks clean).

I am using the internal oscillator at 4MHz with the Turbo
fuse enabled.

Is there anybody else with similar POR problems with the
SX chip?

Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +4640142078
FAX INT +4640947388

1999\02\15@074505 by ruben

Forget about it, I found it myself.

I was enabling the RTCC rollover interrupt a couple
of instructions before I was initiating some
registers for the interrupt routine. One of these
registers was holding a jump offset to be used inside
the interrupt routine. Apparently, because of the random
value of RTCC at power on, a interrupt was generated
before this register was initiated. Putting a clr RTCC
before enabling the RTCC rollover interrupt solved the

And I was sure this was a hardware problem!

{Quote hidden}

Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +4640142078
FAX INT +4640947388

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