> -----Original Message-----
> From: Alan B. Pearce [SMTP:A.B.Pearce@RL.AC.UK]
> Sent: Thursday, February 22, 2001 10:44 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: IIC Routines - giving, not needing
>
> >The read-modify-write operations are performed on the
> >shadow register where there are no problems with this,
> >then the new shadow register value is written (no read) to PORTB.
>
> Humm, I seem to recall a discussion through this list a while back on
> Interrupt
> on Change, and someone demonstrated that a write to a port fouls up the
> interrupt detection the same as a read/modify/write on the port. The write
> does
> actually do a dummy read apparently, even though the info it is writing is
> not
> what was read.
>
> I cannot remember just when the discussion was, you will need to search
> the
> archive - should not be hard with James' new search bot.
>
Even if it does a dummy read, as long as the information it read was
discarded and it transfers your byte to the port latches there should be no
problem.  PORTB Interrupt on change is a whole other ball game though...

Mike

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