On Wed, 7 Jan 2004 10:11:53 -0000, Alan B. Pearce wrote on
Re: [PIC:] Pic as an i2c slave:

>>I still have to fully understand why CKP should be set at
>>that point, but of course I'll believe the gurus...
>>
>>A code comment here says that we should never get to that
>>state; having to add that instruction at that place implies
>>that for the whole thing to consistantly succeed afterwards
>>it first has to fail once and reach this uncontrolled
>>state... Strange...
>
>Umm, not sure about never getting there.

Here is what I am referring to, copied ans pasted from
AN734a.pdf:

State5:
movlw b=9200101000=92; A NACK was received when transmitting
xorwf Temp,W     ; data back from the master. Slave logic
btfss STATUS,Z   ; is reset in this case. R_W =3D 0, D_A =3D 1
goto I2CErr      ; and BF =3D 0
return           ; If we aren=92t in State5,=20
                 ; then something is wrong.
I2CErr:
nop
banksel PORTB    ; Something went wrong! Set LED
bsf PORTB,7      ; and loop forever. WDT will reset
goto $           ; device, if enabled.
return

This comment "something went wrong" seems to imply that the
current state, that leads to i2cErr has no meaning there and
in fact should never happen; it appears to be confirmed by
the pathetic attempt to have the watchdog reboot the PIC by
executing a goto $ instruction...

>I haven't refreshed myself properly
>about how the code works, but from the quick glance through on writing =
the
>previous message, it will get there if the master sends back a NAK when =
the
>slave is sending data to the master. The result is that there is no =
release
>of the clock by the slave for the master to do the next message - i.e. =
the
>slave is doing a permanent clock stretch. Is this what you see on the =
scope
>when your system gives up?

This may be the case and I'll have to investigate into it, I
will try to borrow a storage oscilloscope from my job.

>Will organise the module for you, I have to go turn on a machine on =
another
>floor to get the most current version.

Many thanks again, Alan

* Xrobert.soubie@free.frX (veuillez supprimer les "X")
* http://www.astrosurf.com/soubie
* Au royaume des aveugles, les borgnes sont mal vus... - P.Dac

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