>Hi
>
>I have stumbled on a problem with compatability between
>PICs and the Philips' PCF range I2C real time clocks.
>
>Sometimes the Philips chip just stops responding to
>the bus - it won't ACK for love nor money. Apparently
>this problem does not occur with the Philips or Atmel
>micros - only with PICs.
>
>My questions
>
>1) Has anyone else on this list experienced this?
>2) Does anyone know of a fix (except a power cycle)?
>
>My code is definitely correct.
>
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>

>
> Don't know if this going to be related but it might help others: By
> using the PCF i/o I have found that the PCF needs time to rise and fall
> for Ack/not Ack. I always put a small delay between the SCL pulse for
> LSB and SCL pulse for Ack. As a test put a temporarily long delay
> between the two.
>
> I picked this up on my 'scope. Create a synch pulse (BSF then BCF or
> whatever) on a spare o/p pin just before your Start code and connect
> this on your Y input and trigger the 'scope on Y. Use X1 and X2 for SDA
> and SCL. If your scope got a delay line or Timebase magnifier the use
> that to scroll over your whole train of I2C pulses.
> Then you will see where your slave stops working. You will recognize
> slave control of the SDA when the rise time is longer than the PIC's or
> when it's already high you will see a small indent for every SCL pulse
> on the SDA. You will also see the same indent on a low. (well, at least
> on my projects :)).
>
> I have not studied the Philips RTC properly but doesn't it need time to
> do internal stuff? Or the I2C buffer gets full and it needs time to
> write to the RAM? Then it might just pull the SDA low. Are you using the
> Interrupt pin?
>
> Hope this help. I have never read of any difference of I2C on PIC,
> Philips or Atmel.
>
> Quentin