Rob Zitka wrote:

> Hi,
>
> I am having a problem with a protoype build of a PIC circuit.  I have Port
> B connected to 2 LED's (2 mA each), 3 relays (13 mA each) and 3 to an MAX
> 232 chip.  The chip is a 16C72, windowed.
>
> I wrote a simple program in MicroEngineering Labs PIC Basic to see test the
> operation of the PIC.  It goes as follows:
>
> High 0
> Pause 1000
> Low 0
> Pause 1000
> High 1
> Pause 1000
> Low 1
> Pause 1000
>
> the rest goes on to do the same with the other lines conected to the relays.
>
> RB0 and RB1 operate the status LED's.  I energize the circuit and the LED
> connected to RB0 Blinks on one second then off.  Then the LED connected to
> RB1 doesn't light.  Or sometimes the RB0 LED lights goes off then RB1
> lights and goes off.  Most of the time though the RB1 LED never lights.
>
> Why is the operation of this so intermittent?
>
> I set Watchdog timer OFF during compilation.  The MCLR is connected to a
> DS1233 like Myke Predko recommends.  The crystal is 4 MhZ, with 22pF loads.
>  The current draw on Port B is less than 50mA max.  The circuit is powered
> through a 5V regulator with a 9V battery.  The relays have protection
> diodes on the coils to prevent surge currents from damaging the PIC.  The
> PIC has a bypass cap at the Vdd and Vss.
>
> This has me stumped.

I wish everyone who asked a question stated the circumstances
as completely as this!

The only two things I can think of, are :
1) Check whether the trisb register is guaranteed for output
   before you write to it.
2) Check if one of the delay variables aren't uninitialised.
   Because you use a JW part, the ambient light may affect
   the startup conditions of your RAM.

I would also force the MCLR high during bug hunting.

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za

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