In message  <9801261940.aa12350@device.data.co.za> PICLIST@MITVMA.MIT.EDU
 writes:
> Hi Mike,
>
> > > I am using a 16x1 lcd display with a 16C71. The C71 has a maxim
> > > reset circuit (I think it is a 705, but can't remember exactly).
> > >
> > > If the power to the circuit is removed and then returned quickly,
> > > the display stops working. I guess this is because the 705 resets
> > > the PIC, but the supply doesn't go low enough to properly reset
> > > the LCD.
> > >
> > > Is there a way round this?
> >
> > I should have added that I am using the LCD in 4-bit mode and
> > am not using the r/w pin.
>
> As mentioned you need to carefully follow the initialisation
> procedure and assume nothing about the state of the LCD, it may
> have survived the brownout and initially just have the nibble
> phasing wrong.  The triple command sequence to force it into 8 bit
> mode is used to reestablish the nibble sequence in 4 bit mode, this
> is part of the recommended procedure.
>

I have convinced myself that the initialisation procedure is correct
by going through the code instruction by instruction, comparing it
with the data sheet and examples of code I have found elsewhere on
the web.

Adding some more info, this problem occurs with some manufacturers
displays and not with others. The worst appears to be an Hitachi
display, with some cheap Taiwanese displays never causing a
problem.

I had thought of using a PIC pin to power the LCD, but this will
require a new board layout (or at least some Kynar wire) which I
was hoping to avoid.

It seems to me, that if the display is not being reset properly
when there is a brown-out, that no amount of code trying to
re-configure it will work as the display will not accepting any
commands, so a hardware reset is required. Is this reasonable?
If so, the only solution is to ensure the supply is removed
when the PIC is reset. Right?

Regards,

Mike Watson