On 2010-09-22 13:55, Rolf wrote:
> On 10-09-22 01:02 AM, David Duffy (AVD) wrote:
>>     Up until now, I've only used the older (lower end?) PICs
>>
>> I think I understand the difference between PORTx and LATx, but in one
>> data sheet Microchip show port B being initialised like so:
>>
>> BANKSEL     PORTB
>> CLRF        PORTB
>> BANKSEL     LATB
>> CLRF        LATB
>> BANKSEL     ANSELB
>> CLRF        ANSELB
>> BANKSEL     TRISB
>> CLRF        TRISB
>>
>> Why bother clearing TRISB when you would be only writing to LATB anyway?
>> David...
>>
>>
>
> Good point. All writes to PORTx are written to the latch anyway, so clrf
> PORTx is identical to clrf LATx
>
> The port pin diagrams indicate that fact as well.
>
> Further, all analog pins read as '0', all digital pins read the state of
> the signal (which for outputs may be a mis-match to the LATx value if
> you have slow-changing signal lines...).
>
> But, in all cases, clrf PORTx =3D=3D clrf LATx
>
> On the other hand, it's not an error to do it twice... and further,
> operations other than 'clrf' on PORTx will/may produce a different
> result than the same operation on LATx...

No, all *write-only* operations works the same against PORTx
or LATx. Such as CLRF and MOVWF.

Read-Modify-Write operations may work differently.
Such as BCF, BSF and all and/or/xor operations on a file reg.

Jan-Erik.

> so perhaps it is good practice
> to treat them 'both' explicitly in the initialization routine...

No, there is absolutly no reason for that.

>
> Rolf
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