>
> What would be the best way to create a 5 second delay with a 16c56?

It really depends if you need to do anything else during that delay time.
If not then Sean's delay looping looks really good. PICS are quite helpful
because every instruction's execution time is completely deterministic.

If you need to do somthing else, then using the timer is your best bet.
Be aware that the PIC's timer will have jitter if you write to the
timer register. The upshot is that if you really want anything close to
precise timing, it's best to simply let the timer overflow and count the
overflows.

Here's an example. A 10 Mhz 16F84 timer register will count 2.5 million ticks
per second. We can use the prescaler to reduce this down to exactly 9765.625
tics per second be setting the prescaler to 256. Then if we watch just the
overflow then we'll get 38.14 tics per second. Then all you need to do is
count 190 overflows. This will give you a delay of 4.98073 seconds.

There are two ways to count the overflows. You can use interrupts and
update the count in the interrupt service routine. Or you can keep interrupts
off and watch the overflow bit yourself, updating the count and clearing the
overflow bit. In this case you must be sure that your routine checks the
bit within two overflows (52 ms in this example) or you'll miss a tick.

Lastly to get truly precise timing and keep the no write rule in place you
need to change crystal speeds so that they evenly divide by powers of 2.
For example by switching the crystal to 9.8304 Mhz you can divide evenly
all the way up to 2^17 power. This means that you can use the natural
clock divide by 4, overflow the counter, and prescale by 32, and get precisely
75 overflows per second. Count 375 of these (unfortunately requiring 9 bits)
and get a 5.00000 second delay.

Hope this helps,

>
> Scott
>
> P.S.    Thanks for all the help on PORTA.  About five minutes after I
> sent the message I had about 500 people telling me what to do.  Thank
> god none of you said to give up on PICs.   I am making the transition
> from 68xx and 68xxx to the PICs and the road looks long and far.

It really isn't. PICS work very well because they are simple. However that
simplicity sometimes requires rethinking how you do things, just like in
the PORTA example and the timer stuff here. One learns from experience
things like writing to the timer register messes up the count...

BAJ
>