I do not use that compiler but I have seen your problem before. Some
libraries do not implement Start entirely (they make assumptions about the
line state which are not true here). So I add a proper Stop before the
start and it works. If you look at the implementation of the StartI2C you
should see the problem.

Also, your code calls a lot of functions. Maybe there should be two versions of
the I2C functions and you should use the blocking ones (the ones that already
check for IdleI2C() inside them).

Peter

On Mon, 8 Jul 2002, Harold M Hallikainen wrote:

>I'm having trouble figuring out how to use I2C from within the C18
>compiler. Here's my code
> to read a byte from an X1226:
>
> unsigned char ReadU8eep(unsigned int addr){
> // Read a byte from eeprom chip at addr
> unsigned char data; // Keep our data while we close the I2C
> OpenI2C(MASTER, SLEW_ON); // Initialize the I2C as a master
> // SSPADD=22; // 400 kbps with 40 MHz clock
> SSPADD=0xff;
> IdleI2C(); // Wait for i2c to be ready
> StartI2C(); // Send a start
> IdleI2C(); // Wait for i2c to be ready
> WriteI2C(0xae); // Send the slave address with the r/-w low indicating
>we're writing an
> address
> IdleI2C(); // Wait for i2c to be ready
> WriteI2C(0xff & (addr>>8)); // Send the high half of the address address
> IdleI2C(); // Wait for i2c to be ready
> WriteI2C(0xff & addr); // Send the low half of the address
> IdleI2C(); // Wait for i2c to be ready

  StopI2C(); // Add this

> StartI2C(); // Send a start
> IdleI2C(); // Wait for i2c to be ready
> WriteI2C(0xaf); // Send slave address with r/-w high indicating we're
>reading
> IdleI2C(); // Wait for i2c to be ready
> data=ReadI2C(); // Get the data
> IdleI2C(); // Wait for i2c to be ready
> StopI2C(); // Send an I2C stop
> IdleI2C(); // Wait for i2c to be ready
> CloseI2C(); // Done with I2C
> return(data); // Exit with the data we got
> }
>
>      The documentation on the I2C library only gives sample code for
>talking with Microchip
> EEPROMs, so I had to try to figure out how to talk with the Xicor part.
>I'm assuming IdleI2C()
> is required between instructions to insure the SPP has finished the
>previous instruction.
>      Watching the transaction on a scope, the problem SEEMS to be with
>the StartI2C() after
> sending the low half of the address. After the 8th clock, another clock
>is sent and data is
> held low (I assume by the X1226) for an acknowledge. Then, the clock
>goes low. The
> StartI2C() seems to do nothing. The clock and data both remain low.
>After the acknowledge
> clock (about 12us) is a very short clock (less than 4us). It appears the
>data line is released
> at the same time as the clock line. This MIGHT be an attempt at sending
>a start, but it
> clearly fails. The clock goes low after the 4us or so while data remains
>high through the next
> full clock (the start of sending 0xaf). When we get down to reading data
>back using ReadI2C,
> the data line just stays high. I think the EEPROM ignored the command to
>output its data
> because of the lack of a start.
>      So, anyone done I2C using C18?
>
> Thanks!
>
> Harold
>
>
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