i2c.txt

Hitech microchip PIC C18 Compiler

The i2c functions and macros to implement the i squared c,
7-bit, standard-mode, master-mode protcol.

For a description of i squared c, see "The i2c bus -
and how to use it" by Philips Semiconductors.

CONTENTS
########

1 Setting Up
2 High-level Function and Macro Definitions
3 Lower-level Function and Macro Definitions
4 Examples


1) Setting Up
#############

The file i2c.h should be #included into your source
files. This file contains several macros which specify
which port bits are to be used for the clock (SCL) and
the data line (SDA). These should be adjusted to suit
your application. The bus time-out macro I2C_TM_SCL_TMO
in i2c.h may need adjusting to suit the devices used.
Some devices require relatively long time to process
data. A delay may be required in your code before
attempting further access to these devices. If your
PIC crystal frequency is not 4MHz, you will have to
make the appropriate adjustments as detailed in delay.h
for the delays to be accurate.


2) High-level Function and Macro Definitions
############################################

unsigned char
i2c_WriteTo(unsigned char address)
~~~~~~~~~~~

This function is used to commence writing to a device
on the bus. Specify the 7-bit address to which data is
to be sent. The least significant bit of the argument
is ignored. The function generates a (re)start condition
and reads an acknowledge from the slave. The function
returns TRUE if the slave did not acknowledge the address
transfer or FALSE otherwise.

unsigned char
i2c_ReadFrom(unsigned char address)
~~~~~~~~~~~~

This function is used to commence reading from a
device on the bus. Specify the 7-bit address from which
data is to be read. The least significant bit of the
argument is ignored. The function generates a (re)start
condition and reads an acknowledge from the slave. The
function returns TRUE if the slave did not acknowledge
the address transfer or FALSE otherwise.

signed char
i2c_PutByte(unsigned char byte)
~~~~~~~~~~~~

This function is used to send a byte of data to the
device which has been activated by i2c_WriteTo().
The function checks the acknowledge bit returned
by the slave. The function returns I2C_ERROR if during
the transfer a bus error occured, TRUE if the data
was not acknowledged, or FALSE if the transfer took
place without error and was acknowledged.

int
i2c_GetByte(unsigned char more)
~~~~~~~~~~~

This function is used to read a byte of data from
the device which has been activated by i2c_ReadFrom().
The argument to this function is used to determine if
more data is to be read from the activated device. If
more is I2C_LAST, or false, no acknowledge is sent, and
no more data can be read from the activated device
unless another i2c_ReadFrom() command is issued.
If more is I2C_MORE, or any true value, an acknowledge is
sent and more data can be read from the activated
device. The function returns the unsigned byte read
from the activated device or I2C_ERROR if a bus error
occured during the read operation.


signed int
i2c_PutString(const unsigned char *string,
~~~~~~~~~~~~~       unsigned char str_len)

This function is used to send a sequence of bytes to
the device which has been activated by i2c_WriteTo().
The function attempts to send str_len bytes which
are read from string. If a bus error occures during
the transfer, the function returns a negative int.
The magnitude of this number is the number of bytes
which were not successfully transmitted. If the
slaves fails to acknowledge a transfer, the
transmission is terminated and the function
returns a positive number. The magnitude of this
number is the number of bytes which were not
successfully transmitted. The function returns FALSE
if the all the bytes were transmitted without error
and they were all acknowledged by the slave.

unsigned char
i2c_GetString(unsigned char *string,
~~~~~~~~~~~~~ unsigned char str_len)

This function is used to obtain a sequence of bytes
from the device which has been activated by
i2c_ReadFrom(). The function attempts to read str_len
bytes which will be stored at string. If a bus error
occurs during the transfer, the function terminates
and returns the number of bytes not successfully read.
The function returns FALSE if all the data requested
was read without error. This function indicates to
the slave that no more data is to be read after
successfully reading the last byte. To read more data
after using this function, activate the source device
by using i2c_ReadFrom().


I2C_MORE and I2C_LAST
~~~~~~~~     ~~~~~~~~

These macros may be used with i2c_GetByte() to
indicate that more data is to be read or that this
is the last byte to be read, respectively.

I2C_ERROR
~~~~~~~~~

This macro may be used with i2c_GetByte() and
i2c_PutByte() to check for a bus error.


3) Lower-level Function and Macro Definitions
#############################################

void
i2c_Stop(void)
~~~~~~~~

Sends a stop condition.

void
i2c_Restart(void)
~~~~~~~~~~~

Sends a start condition.

void
i2c_Start(void)
~~~~~~~~~~~

Sends a start condition. Functionally the same
as i2c_Restart().

unsigned char
i2c_SendByte(unsigned char byte)
~~~~~~~~~~~~

Sends an 8-bit number to the active device. The
acknowledge bit is not checked. Returns TRUE if
a bus error occured; FALSE otherwise.

usigned char
i2c_SendAddress(unsigned char address,
~~~~~~~~~~~~~~~      unsigned char rw)

Sends an 8-bit quantity representing a 7-bit
address and a 1-bit read/write mode bit. Returns
TRUE if a bus error occurred; FALSE otherwise.

signed char
i2c_ReadAcknowledge(void)
~~~~~~~~~~~~~~~~~~~

Reads the acknowledge bit from the slave.
Returns I2C_ERROR if a bus error occurs, TRUE if
the device did not acknowledge, or FALSE
otherwise.

int
i2c_ReadByte(void)
~~~~~~~~~~~~

Reads an 8-bit quantity from the slave. The
acknowledge is not generated. Returns the byte or
I2C_ERROR if a bus error occurred.

void
i2c_SendAcknowledge(unsigned char status)
~~~~~~~~~~~~~~~~~~~

Sends an acknowledge if status is TRUE; sends
a ~acknowledge otherwise. A ~acknowledge is used
to indicate to the slave that no more data is to
be read and that it should release the bus so that
the master can issue the next command.

unsigned char
i2c_Open(unsigned char address, unsigned char mode)
~~~~~~~~

Sends a 7-bit address and 1-bit read/write mode bit.
Returns TRUE if the device did not acknowledge.

unsigned char
i2c_WaitForSCL(void)
~~~~~~~~~~~~~~

Waits for the clock line to be released by the slave.
If the line is not released after I2C_TM_SCL_TMO micro
seconds, the function times out and a bus error is
assumed. In this case, the function returns TRUE;
FALSE otherwise.


4) Examples
###########

i2c_WriteTo(0xAE);	/* talk to device 1010111w */
i2c_PutByte(0x00);	/* send data 0x00 */

i2c_ReadFrom(0xAE);	/* talk to device 1010111r */
data1 = i2c_GetByte(I2C_MORE);	/* read one byte */
data2 = i2c_GetByte(I2C_MORE);	/* read another */
i2c_GetString(my_string, 10);	/* read 10 bytes */

/* i2c_GetString() terminates reading, if more data
 * is required, re-address the device
 */

i2c_ReadFrom(0xAE);
data3 = i2c_GetByte(I2C_LAST);	/* last byte read */

/* check for errors */
if(i2c_PutByte(0xff))
  my_error_routine();	/* bus error or ~ack */