Hi, I'd like to test the clamp voltage for a surge supresor, could some one
help me with this kind of test. Regards Julio

> -----Mensaje original-----
> De:   Tobie Horswill [SMTP:thorswil@EXMACHINA.QC.CA]
> Enviado el:   Tuesday, September 25, 2001 9:31 AM
> Para: PICLIST@MITVMA.MIT.EDU
> Asunto:       [PIC]: strange MSSP slave behaviour
>
> Hi, I've got 2 x F877 talking to each other via i2c. One master and the
> other slave. My i2c master routines work fine with a 24LC64 EEPROM and
> also
> with an i2c LCD module on the same bus. When I try sending stuff to the
> slave PIC however things get a bit weird.
>
> I've used Microchip's AN734 source almost textually (added a few
> diagnostic
> LEDs and Tony Nixon's ROMZap) for the slave PIC. The applications note's
> code seperates all incoming i2c events into 6 possible states.
>
> 1: Master write, last byte was an address (SSPSTAT = XX0X 10X1)
> 2: Master write, last byte was data (SSPSTAT = XX1X 0X10)
> 3: Mater read, last byte was address (SSPSTAT = XX0X 11X0)
> 4 Master read, last byte was data (SSPSTAT = XX1X 11X0)
> 5 Master NACK (SSPSTAT = XX1X 10X0)
> 6 all other SSPSTAT configurations will generate an error condition
>
> START, STOP and ACK events being taken care of automatically by the MSSP
> hardware I assume.
>
> Now, if I send the standard i2c write "stream" of START, ADDRESS, DATA,
> STOP
> from the master  (waiting for ACKS from the slave after each byte), the
> slave should first fall into state 1 after the ADDRESS event and then into
> state 2 after the DATA event right ? Well, it doesn't. Instead it always
> ends up branching to state 6 at some point (I haven't been able to
> identify
> where yet). Everything works fine if I insert a 1mSec delay after the
> ADDRESS and DATA bytes from the Master though. I tried replacing the 1mSec
> delay by one or more NOP but it's not enough. Why the delay since the
> master
> waits for (and DOES receive) an ACK from the slave before sending the next
> byte ?
>
> MSSP baudrate generator is set to 100kHz, i2c threshold levels are
> selected,
> slew rate control is disabled, 2.2k pull-ups on SDA and SCL (also tried
> 4.75k), tried removing the EEPROM and the LCD from the bus. no cigar.
>
> Any ideas ?
>
> kind regards,
>
> _______________________
> Tobie Horswill
> thorswil@exmachina.qc.ca
>  Ex Machina
> 103, rue Dalhousie
> Quibec (Quibec) CAN
> G1K 4B9
>
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