This must have been it, it works great now, thanks Bob, and all who
replied.  Case closed!

/Nick

Bob Axtell wrote:

> I2C devices, when powering up, can be accidentally placed inside a READ
> or WRITE sequence due to its detecting a false start.
>
> I always issue a STOP then a START then a STOP after powerup. It fixes
> ALL I2C chips on the bus.
>
> --Bob
>
>
>
> Dmitriy Fitisov wrote:
>
>> I think you are talking about START byte - see I2C specification
>> 10.1.2 for version 2.1
>> Basically it used for slaves which are software-coded, and in some cases,
>> yes, slave remembers last address it was addressed with - see 10-bit
>> address
>> READ mode - it sets address in WRITE mode, after that send repeated
>> START,
>> 2-nd byte of the address with READ byte.
>>
>> Dmitriy
>>
>> -----Original Message-----
>> From: pic microcontroller discussion list
>> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Nick Veys
>> Sent: March 7, 2004 4:50 PM
>> To: PICLIST@MITVMA.MIT.EDU
>> Subject: [PIC]: I2C Guru's, Help!
>>
>>
>> Ok, this has to be a quirk of I2C that I'm not aware of, this is odd.
>>
>> I'm using a PIC18F2320 to talk to a Matrix Orbital GLK12232-25SM LCD, It
>> has a 16C87 on it FYI.
>>
>> I was having trouble talking to it so I thought I had the address wrong,
>> I wrote a loop to go though all possible addresses, and bingo it worked.
>>   So I binary searched til I found it, decimal 80, which was what I
>> thought it was in the first place.  So I took the loop out and tried to
>> talk to 80, no luck.  What the hell I say to myself. :)
>>
>> So I play around a bit and find that if I try to send data to it without
>> first having tried to send data beforehand, ANY data, it won't work.
>> But if I just send 0x00 to address 0x00 (or anything to anything) it
>> works fine.
>>
>> So I'm guessing it's some kind of reset condition on the I2C bus?  I set
>> SDA/SCL high before starting anything and that didn't seem to do
>> anything, maybe something in the PIC that gets setup after the first
>> run?  Seems odd but I'm out of ideas here! :)
>>
>> Here's my code to illustrate if I'm doing something absurd:
>>
>> --------- SNIP ------------
>> void init() {
>>    TRISC = 0b10000000; // See pinout
>>
>>    SMP = 1; // Slew Rate Standard (100KHz - 1MHz)
>>    SSPADD = 19; // I2C clock = 8M/(4*(19+1)) -> 100KHz
>>    SSPCON1 = 0x08; // Master, clock from SSPADD
>>    SSPEN = 1; // Synch. Serial Port Enabled
>> }
>> void sendI2C(unsigned char addr, char* data, unsigned char len) {
>>    unsigned char i;
>>
>>    SSPIF = 0; // Clear SSP flag
>>    SEN = 1; // Start Enable
>>    while(SEN); // Wait to finish
>>    SSPIF = 0; // Clear SSP flag
>>    SSPBUF = addr; // Send address
>>    while(!SSPIF); // Wait for SSPIF flag
>>    SSPIF = 0; // Clear SSP flag
>>    for(i = 0; i < len; i++) {
>>      SSPBUF = data[i]; // Send data
>>      while(!SSPIF); // Wait for SSPIF flag
>>      SSPIF = 0; // Clear SSP flag
>>    }
>>    PEN = 1;
>>    while(PEN); // Wait to finish
>>    SSPIF = 0; // Clear SSP flag
>>
>>    delayMilliseconds(1);
>> }
>>
>> void sendStuff() {
>>    char data[] = { 0xFE, 0x62, 2, 0, 0 };
>>    char len = 5;
>>
>>    sendI2C(80, data, len);
>>    sendI2C(80, data, len);
>> }
>>
>> void main() {
>>    init(); // setup ports, registers, etc...
>>
>>    delaySeconds(2); // wait for everyone to wake up
>>    sendStuff();
>>
>>    while(1);
>> }
>> ------------- SNIP --------------
>>
>> This works.  If I change sendStuff() to have just 1 sendI2C, it doesn't
>> work.  Any suggestions are appreciated on the code as well of course.
>>
>> Thanks!
>>
>> Nick
>>
>> --
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>
>
> --
>
>  Replies: NOTE-Script, EXE,BAT and COM
>     files will be rejected by server
>              --------------
>                Bob Axtell
>        PIC Hardware & Firmware Dev
>          http://beam.to/baxtell
>              1-520-219-2363
>
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