8-bit Microcontrollers中的主题 Best way to control port bits

Best way to control port bits

Bloodhound — Mon, 24 Sep 2007 21:05:56 GMT

Hi all,

So which of the below is 'acceptable' or most code efficient? Or does it not matter?

lda   #%00000000   ; Set up Port A values before turning on.
sta   PORTA        ; Values to Port A
lda   #%11110011   ; Set up Port A pullups before turning on.
sta   PTAPUE       ; Enable some pullups
lda   #%00000000   ; Store Port A Data Directions.
sta   DDRA         ; Configures Port A[7..0] as inputs

mov   #%00000000,PORTA    ; Set up Port A values before turning on.
mov   #%11110011,PTAPUE   ; Set up Port A pullups before turning on.
mov   #%00000000,DDRA     ; Store Port A Data Directions.

Thanks,

Ross

Message Edited by Bloodhound on 2007-09-25 12:23 AM

Re: Best way to control port bits

tonyp — Mon, 24 Sep 2007 21:24:56 GMT

In theory, it doesn't matter. But, for port setup, specifically,

1. STA is best for dynamic changes (value in A may change periodically, but not using the immediate mode as in your example, in which case I prefer [2] below).

2. MOV is best for static initialization (always the same value is written to the port at the specific point of execution), and it is shorter than [1].

3. Best for single bit changes but only after original initialization. Using BSET/BCLR for first time setup is risky (as it blindly copies the remaining bits with whatever random values they happen to carry), a problem with write-once registers, for example. (Did you just edit [3] out?)

Re: Best way to control port bits

Bloodhound — Mon, 24 Sep 2007 21:50:14 GMT

Thanks TonyP,

Yes I did Edit out point 3. Sorry about that.

Cheers,
Ross

And I edited this due to a spelling mistake

Message Edited by Bloodhound on 2007-09-25 12:50 AM