Steve Kasm wrote:
>
> Hi All,
>
> Apparently if you have an interrupt on the tmr0 overflow active, in my
> case this interrupt is updating the data in a 4511 and driving 4
> transistors for a 4 digit LED display, then outputs on the PortB will
> not latch when the interrupt is running. By disabling the interrupt and
> blanking my display in code I was able to get the portb,5 port to latch
> it's output for my purpose.
>
> I guess you learn something everyday.
>
> Thanks all for your help

Your interrupt is probably overwriting the data on PORTB,5 causing it to
be reset to 0.

When you write the digit data to PORTB are you preserving the RB5 data
bit.

For example, if you know RB5 is high (Relay = On) and you also want RB0
to go high then you must write b'00100001' to PORTB. If RB5 is low
(Relay = Off) then you must write b'00000001' to PORTB.

You can have a Shadow register to do this task.

Shadow_B

At the start of the code

  clrf PORTB
  clrf Shadow_B  ; = same as PORTB


In the Interrupt routine, say setting RB0...

        bsf Shadow_B,0

        movf Shadow_B,W
        movwf PORTB


In the MainLoop code, say turning on the relay

        bsf Shadow_B,Relay

        movf Shadow_B,W
        movwf PORTB

If the Interrupt routine executes every 5mS or so to keep the displays
refreshed, then all the MainLoop code has to do is..

        bsf Shadow_B,Relay

The Interrupt will update PORTB from the Shadow_B register.




--
Best regards

Tony

mICros
http://www.bubblesoftonline.com
mailto:sales@bubblesoftonline.com

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