PIC: Dumb question re banksel

[augustinetez]

The dumb question using a 16F628 as an example:-

OPTION is in banks 1 & 3 and TMR0 is in banks 0 & 2.

When using banksel for things like OPTION_REG or TMR0 and considering that these exist in two different sets of banks, which bank does it select?

I've been using banksel for these registers for a little while and not knowingly come across a problem doing it - just curious as to possible problems, if any.

 

[Pommie]

When I programmed in Asm I kept away from banksel as it always produces two instructions when one or even none are needed. I now realise that it's irrelevant as the processor is so fast (fast enough to use C).
I know you can do it either way but why not use the option instruction (now deprecated) to set the option register?

Mike.

 

[jpanhalt]

A quick simulation (MPLAB SIM) with this code:

Showed RP1 and RP0 bits of STATUS for TMR0 as 00 ( Bank 0) and for OPTION_REG was as 01 (Bank 1). I don't usually use the banksel directive, as I track what bank I am in to minimize switching when practical.

 

[augustinetez]

Mike, at some stage, I forget if it was an older PIC or a newer enhanced one, I kept getting an error message when trying to use the 'option' instruction, hence I've used option_reg ever since.

JP, thanks for that, answers the question.

I also do my best to group as much code as possible to minimise switching banks.

 

[Pommie]

Mike, at some stage, I forget if it was an older PIC or a newer enhanced one, I kept getting an error message when trying to use the 'option' instruction, hence I've used option_reg ever since.

Are you saying that the option instruction no longer works? It was deprecated but I thought it had a few years before being removed.

Mike.

 

[Nigel Goodwin]

Are you saying that the option instruction no longer works? It was deprecated but I thought it had a few years before being removed.

Mike.

I thought it had been removed many years ago? - but I can't say I've ever tried it recently?. As far as I'm aware it was 'depreciated' last century?.

 

[Pommie]

Last century is a rather silly term, most of what I did was last century.

Mike.

 

[augustinetez]

The 16F628 datasheet mentions it was left in to be compatible with 16C5X chips and should not be used for newer chips.

As to when it actually stopped working I don't know, I'm incapacitated at the moment, so might compile for a few different PICs tomorrow and see where it stops.

 

[jpanhalt]

Last century is a rather silly term, most of what I did was last century.

Mike.

A lot of us have been deprecated.

OPTION still works with enhanced mid-range (e.g,, 16(12)F1xxx chips. It gives a warning, however:

Warning[224] D:\.... : Use of this instruction is not recommended.

 

[augustinetez]

Maybe that's what I saw rather than an error - it was quite a while ago so very likely.

 

[jpanhalt]

It may depend on the assembler too. I use MPLab 8.92 (MPASM 5.49).

 

[augustinetez]

Same here.