Harold:
I would that invoking the read while writing will _immediatly_ change
from writing to reading. Very bad.

Also, be aware that changing the EEPROM data or address while writing
will cause the EEPROM hardware to start writing with the original
data/address and finish writing with the new data/address. Also very
bad.

If you want to put the check for EEPROM ready at the start of the EEPROM
subroutine then you must use temporary variables to hold the data and
address until the EEPROM is ready to accept the updating of the EEPROM
data and address registers.

I hope this makes sense. If not, I can give an example.


-- Rich



Harold M Hallikainen wrote:
>
>         In my code, I've done the check for end of write on the way in to the
> write routine instead of on the way out, figuring that I could get other
> stuff done before I get stuck in a loop waiting for the eeprom write to
> finish. As I think about it more, though, are reads inhibited until the
> write cycle is complete? This is the case with the 2816 EEPROM with which
> I am more familiar. So, maybe it IS a good idea to wait for the write to
> finish before doing anything that might try to read the eerpom.
>
> Harold
>
> On Tue, 16 Jan 2001 09:20:01 -0500 Drew Vassallo <snurple@HOTMAIL.COM>
> writes:
> > You may have also forgotten another line, I can't remember exactly if
> > it's
> > required - I haven't used it in a while.  Try this:
> >
> >                 bsf     STATUS, RP0     ; select Bank1 for EECON
> > access
> >                 bcf     INTCON, GIE     ; disable interrupts
> > temporarily
> >                 bsf     EECON1, WREN    ; enable EEPROM write
> >                 movlw   0x55
> >                 movwf   EECON2
> >                 movlw   0xAA
> >                 movwf   EECON2
> >                 bsf     EECON1, WR      ; write values to EE
> >                 bsf     INTCON, GIE     ; reenable interrupts
> >                 bcf     EECON1, WREN    ; disable EEPROM write
> > Waitforflag
> >                 btfss   EECON1, EEIF    ; poll flag bit
> >                 goto    Waitforflag
> >                 bcf     EECON1, EEIF    ; write cycle complete
> >                 bcf     STATUS, RP0     ; leave Bank0 active by
> > default
> >                 return
> >
> > --Andrew
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