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PICList Thread
'Emulation Help needed'
1997\05\24@225033 by ernie Gordon

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I am having difficulty emulating with a PIC16C74.  I am using a RICE16
emulator, and looking for a change in PORTB.  I have set INTCON to a hex C8,
and PB2 thru PB7 are setup for input, with weak pullups.  When I ground PB4,
the emulator processes the interrupt, but performing a read on PORTB does
not enable me to clear bit 0 of INTCON.  Can anyone help me with this problem?

If the input is transient, and returns to '1' immediately during the
interrupt there is no problem, but if the input remains at '0', difficulties
ensue.

Please Help

Thanks,

Bernie Gordon

1997\05\29@220818 by ernie Gordon

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>Date: Sat, 24 May 1997 21:46:42 -0500
>To: pic microcontroller discussion list <spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
>From: Bernie Gordon <.....bgordonKILLspamspam@spam@postoffice.worldnet.att.net>
>Subject: Emulation Help needed
>
>I am having difficulty emulating with a PIC16C74.  I am using a RICE16
emulator, and looking for a change in PORTB.  I have set INTCON to a hex C8,
and PB2 thru PB7 are setup for input, with weak pullups.  When I ground PB4,
the emulator processes the interrupt, but performing a read on PORTB does
not enable me to clear bit 0 of INTCON.  Can anyone help me with this problem?
>
>If the input is transient, and returns to '1' immediately during the
interrupt there is no problem, but if the input remains at '0', difficulties
ensue.
>
>Please Help
>
>Thanks,
>
>Bernie Gordon
>

1997\05\30@005643 by Steve Hardy

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Strange that you should mention this now -- I am having a very similar
problem with the external interrupt, using the same bondout chip.
Although I can't offer help with your problem, I will tell you about
mine, which may help jog someone's memory of how they overcame this
problem.

I am _not_ using weak pullups, and trying to use RB0 as an external
interrupt.  The input is an analogue level so I am relying on the
supposed schmidt trigger action of RB0 when used as an input.  Well
the funny thing is that when the input voltage is between the trip
points of the schmidt trigger, the interrupt routine is unable to
clear the interrupt flag in intcon.  I can see this when stepping
through the bcf intcon,intf instruction.  (Actually, sometimes it
clears, but mostly it does not.  I am monitoring the input on an
oscilloscope and I'm fairly sure there are no spikes -- everything
is dead quiet when I pause the emulation).  Naturally, this causes the
interrupt routine to retain control forever after.  Dammit, I am going
to have to insert an external schmidt trigger!

Regards,
SJH
Canberra, Australia

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