> Van: Radboud Verberne <R.Verberne@HSBOS.NL>
> Aan: PICLIST@MITVMA.MIT.EDU
> Onderwerp: PIC Interfacing Serial EEPROM
> Datum: maandag 14 september 1998 15:16
>
> Hello Everybody,
>
> I'm busy with a project to operate a old Nokia MD 59 ATF2 telepfone on
the
> 70cm band (430-440Mhz). I want to use a EEPROM to store some data on it.
> (last used frequency, shift, ctcss etc.) On the Internet I found a piece
of
> code for a 16c84 written in C (in the POST card from Plamen Vaysilov).
When
> I was tranlating I saw that he never looked if the slave (24c65 in his
> case) acknowledged the i2c signals. Plamen Vaysilov is also NOT using
> pull-up resistors!?
>
> Could this be a problem?

I think he uses the internal (weak) pull-ups for port B ...

> I thought that you had to use some pull-up resistors (2k2 at 400Khz, 10k
at
> 100Khz) and then put the SDA into High impedance to output a logic "1"
and
> configuring the SDA line as an Output with the output set to zero for a
> logic "0".
>
> What is the best method? Only configure the SDA as an input when nessarly
> or always as an input when a Logical "1" is needed?

Use the second.  That way the slave _can_ pull the line down whenever he
wants, without creating a short.  Please use this method for _both_ lines
(you never know).

> Please send me a personal message because i'm not subscribed to the PIC
list.
>
>
> Well this is my translated version...
>
>
;*************************************************************************
> ;               I2C Routines
>
;*************************************************************************
> i2cdelay
>         nop
>         nop
>         nop
>         nop
>         nop
>         nop
>         return

You could use a  "Goto $+1" to replace 2 NOP's ...  A CALL to the RETURN
statement uses 4 cycles, but uses one stack ...

Greetz,
  Rudy Wieser

Nijmegen, the Netherlands !