Quoting Martin.Buehler@KEYMILE.COM:

> i haven't read the whole discussion, so i don't exactly know what's the
> original problem.
> as i've used i2c software drivers for a long time, i think i can tell you
> what my main mistakes were when implementing this on a pic:
>
> - never pull a bus high by the pic! pulling high is done by the pull-up
> resistors.

Are you saying that I should be using pull-up resistors on the bus? Because as
it is, I am not... what is the reason for this?

>
> - only use the tris register for the whole communication, i.e. clearing
> tris bit is 'send 0', setting tris bit is 'send 1' or 'input'.
>

And I shouldn't be communicating using bsf/bcf on the ports.. instead use the
TRIS bits? This seems odd.

> - on each write access to a tris bit, clear the appropriate port bit (set
> it to 0)!!!
>   (if you use the same 8bit port of the pic for other purposes, i.e. bits
> 0 and 1 are i2c and bits 2..7 are other outputs, then any bit-write access
> to bits 2..7 may set port bits 0 and 1 to '1', while they are used as
> inputs (tris bit is '1')). pic's don't know any bit manipulations. always
> the whole byte is read and written!!
>
> therefore it is mandatory to always set port bits, used for i2c back to
> '0' again.
>
> maybe, this can help a bit.
> tino
>
>

I'm not sure why I would be getting successful ACK pull-downs from the slave
if I was doing this wrong. Maybe you would know why since you have had more
experience... do you have some example code that sends/reads bytes from a
device?


>
>
>
> Jai Dhar <jdhar@ENGMAIL.UWATERLOO.CA>
> Gesendet von: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>
> 03.02.03 14:56
> Bitte antworten an pic microcontroller discussion list
>
>
>         An:     PICLIST@MITVMA.MIT.EDU
>         Kopie:
>         Thema:  Re: [PIC]: f877 I2C routines
>
>
> Quoting Olin Lathrop <olin_piclist@EMBEDINC.COM>:
>
> > > > You should do a bus STOP here, followed by a bus START before the
> next
> > > > command.
> > >
> > > Regarding this, in the command sequence diagram, it shows just to just
> > send a
> > > BUS Start bit, not stop and start. I was doing this, but neglected to
> > mention
> > > it.
> >
> > That should be OK.  All devices are supposed to reset their bus logic on
> a
> > start, regardless of what state it was in at the time.  In multi-master
> > mode doing just a start is actually a good idea so that no other master
> > can get in there between commands.
> >
> > > And yes, on the ninth clock cycle, I set the TRIS bit so that SDA
> > becomes an
> > > input.
> >
> > You should do that in the low phase before the ninth clock cycle, not
> "on"
> > the ninth clock cycle (whatever that means).
> >
> > > That's how it seems to get pulled low successfully.
> >
> > Huh?  Setting the TRIS bit should cause SDA to float high.  Something is
> > very wrong if setting the TRIS bit causes SDA to go low.
>
> My mistake (again). SDA doesn't get pulled low BEACUSE of the TRIS bit.
> All I
> meant was that I know I was setting the TRIS bit at the right time since
> it
> was successfully getting pulled low by the Slave :-) Like I mentioned,
> when I
> changed the address to something not of the slave, it didn't respond by
> pulling it low, so that's how I know the TRIS part is ok. I am afraid that
> it
> might be something in my reading sequence that is wrong - but I'm not sure
> what.
>
>
> >
> >
> > *****************************************************************
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> > (978) 742-9014, http://www.embedinc.com
> >
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