Jan-Erik Soderholm wrote:
> On 2010-09-22 09:06, David Duffy (AVD) wrote:
>> So to be clarify, I don't understand why Microchip are setting LATx
>> *and* PORTx during initialisation in their example.  Setting PORTx seems
>> to be totally redundant in devices that have LATx registers.
>>    =20
>
> Yes, that is redundant.
>
> B.t.w, *which* datasheet is this ?
> I'd like to verify the context this was written in.
>  =20

PIC16F1934 - document DS41364D

> When *writing*, PORTx and LATx are setting the same
> internal registers in the PIC (the "output latch").
> So when writing (CLRF, MOVWF...) it doesn't matter if
> you use LATx or PORTx, the effect is exactly the same,
> the data is written in the "output latch".
>  =20

That's why I thought it odd that Microchip clear both (effectively the=20
same) in their example.  It wouldn't be the first time their examples=20
were not the best.

> Note that *ALL* PIC has "output latches", they are just not
> directly readable on some PICs (those without LATx registers).
> If not, there wouldn't be anyplace for the PIC to "remember"
> the value written to the PORT, right ?
>  =20

Well yes, I was making the distinction that the LATx was a register in=20
the sense that is was accessible.

> It's very much the same as the fact that on some (older)
> PICs the "working register" ("W") is not mapped as a
> "file register". On PIC18 and the newer PIC16F1xxx there
> is a mapped "WREG" SFR register that can be used for
> BCF/BSF/RRF/RLF or similar instructions that are otherwise
> not usable directly against "W".
>  =20

Ooh, I hadn't noticed that yet.  There's been a few times I wished I=20
could rotate operate on W directly.
David...

--=20
___________________________________________
David Duffy        Audio Visual Devices P/L
Unit 8, 10 Hook St, Capalaba 4157 Australia
Ph: +61 7 38235717      Fax: +61 7 38234717
Our Web Site: www.audiovisualdevices.com.au
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--=20
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