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I was wondering if it is possible to use the assembly command "@sleep" to have a 12c508a chip stop execution and then start again where it left off after sensing an input level change.
I am worried that it will reset execution at the start of the program.
It'll work just fine, but WDT must be OFF otherwise it'll reboot the PIC.
Thanks for the tip on WDT. I'll give it a try today.
It's amazing what can be accomplished by using PIC's.
The 12C508A series can only wake-up from SLEEP with a device reset like /MCLR, WDT timeout, or wake-up on pin change.
The catch is - that even wake-up on pin change with the 12C508A causes a device reset, and you're starting over again from square #1 after any wake-up event.
The good news is - the 12C67x series can wake up from SLEEP & then continue execution at the instruction immediately after the SLEEP instruction if you have global interrupts disabled (GIE=0).
With global interrupts enabled (GIE=1), the 12C67x will wake-up, then execute the instruction after the SLEEP instruction, then branch to the interrupt vector at location 0004h assuming you have an interrupt handler in place.
So on the '508 series it always reboots regardless of the enable WDT settings?
Bummer. The '508 series are typically the most inexpensive PIC's.
> Bummer.
Not quite... all you have to do at the start of your program is check the GPWUF bit in the STATUS register
eg...
If STATUS.7=1 then goto WakeFromSleep
See Datasheet section 8.7 and section 4.3. I keep saying to everyone, you gotta read those Datasheets - or if like me, reading Datasheets isn't your thing on cold winter nights, then at least get to know where things are found so you can jump straight to it - all Microchips Datasheets follow the same layout.
PS. If you want to play with little PIC's then 12F675 is the way to go... they're almost the price of the 12C508/9 and still dropping.
Melanie
Yep - you're still in charge if you know where to look...;o]
I agree with Melanie. If you want the best bang-for-the-buck, then go with the 12F675 or 12F629. They have a few more features, are re-programmable, and only a few pennies more than the 508 series.
Took a look at the 12F629. Goodbye '508, Hello Flash memory!
Thanks Melanie and Bruce for your good advice.