On Wed, 05 Apr 2006 22:18:39 +0200, Barry wrote:

>This one seems worth mentioning as I couldn't find it anywhere on the 
>web. I was porting the Weeder frequency counter code (from the Piclist 
>site) to the 16F6xx chips and I got really stuck. I'd disabled the 
>comparators and changed the variables addresses but it still wouldn't 
>work on the 628 - stranger still, it seemed to work OK in MPSIM but not 
>on the actual chip. Eventually I noticed that the F84 code uses the IRP 
>bit of the status register as a bit variable of its own, setting or 
>clearing it to indicate overflow in a calculation routine. This still 
>seems to work in MPSIM but not on the chip. Changing this bit variable 
>to use a normal file register got the code working OK. So, hopefully not 
>many people do this, but any F84 code which uses the IRP bit may work 
>differently on the 628.
>

The IRP and RP1 bits don't affect operation of the 16F84 since it only
has two RAM banks. There's a note in the 16F84A datasheet:

--quote--

Note 1: The IRP and RP1 bits (STATUS <7:6>) are not used by the
PIC16F84A and should be programmed as cleared. Use of these bits as
general purpose R/W bits is NOT recommended, since this may affect
upward compatibility with future products.

--end quote--


Regards, Bob

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