I have a recommendation:

look at using an external 2N3904 NPN and bias resistor, your solid state
switch probably only needs a strong current source or sink, not both.

Also you can get single surface mount gates in the Fairchild Semiconductor
"Tiny Logic" line.

It is just my opinion that tying two outputs together _just_ for the extra
current is asking for trouble in a big way, and probably bad design.  Just
instinct there though.


On Tue, 25 May 1999, Glen wrote:

> hi & thanks for your time
> problem
>
> with my prog.
> testing using an f84 , but is eventually going to be used in a 12c508
>
> i have a delay & want to toggle 2 o/ps together.
> they need to turn on & off together to supply enough current for a solid
> state switch.
> i don't want one of the pins to blow.
> one pin will not supply enough current on its own.
> i don't want to risk it. AT ALL !!
>
> ******** PORTB,3 is used for zero crossing ************
>
> originally i had
>
> ;       ==============toggle outputs =============
> tog        bsf     PORTB,4     ;set PORTB bit 4 high
>            bsf     PORTB,5     ;set PORTB bit 5 high
>            MOVLW   0x04
>            MOVWF   togh
> delh       DECFSZ  togh
>            GOTO    delh
>
>            bcf     PORTB,4     ;set PORTB bit 4 low       }
>            bcf     PORTB,5     ;set PORTB bit 5 low      }
>            MOVLW   0x02
>            MOVWF   togl
> dell       DECFSZ  togl
>            GOTO    dell
>
>            BTFSC   PORTB,3     ;skip next if 0 , checks for 0 ac cycle
>            GOTO    tog
>            RETURN
>
> ************
> when i change the bsf code to
>            MOVLW b'00110000'
>            MOVWF PORTB
> it still works
> **************
> when i change the bcf code to
>             MOVLW b'00000000'
>             MOVWF PORTB
> it still works
> *****************
>
> i wanted to just use 2 registers
> " on " to replace the bsf's
> " off " to replace the bcf's
> but this won't work !!
> =======vars=====
> on    equ    b'00110000'    ;set portb 4 & 5 to 1
> off   equ    b'00000000'    ;set portb 4 & 5 to 0
> ====prog====
> tog        MOVF    on,PORTB ( to replace bsf's)
>            MOVLW   0x04
>            MOVWF   togh
> delh       DECFSZ  togh
>            GOTO    delh
>
>            MOVF    off,PORTB (to replace bcf's)
>            MOVLW   0x02
>            MOVWF   togl
> dell       DECFSZ  togl
>            GOTO    dell
>
>            BTFSC   PORTB,3     ;skip next if 0 , checks for 0 ac cycle
>            GOTO    tog
>            RETURN
>
> there's no o/p's at all !
>
> i also wanted to use 2 registers for the literals too
> togh    equ    0x04
> togl    equ    0x02
>
> thanks for your advice
> glen
>