ZBasic System Library
160
ZBasic Microcontrollers
Type
Function returning Integer
Invocation
I2CCmd(channel, slaveID, writeCnt, writeData, readCnt, readData)
Parameter
Method
Type
Description
channel
ByVal
Byte
The I2C channel number (0-4).
slaveID
ByVal
Byte
The identifier of the I2C slave device (in the 7 high order bits).
writeCnt
ByVal
integral
The number of bytes to write (0 – 65535).
writeData
ByRef
any type
The variable containing the data to write.
readCnt
ByVal
integral
The number of bytes to read (0 – 65535).
readData
ByRef
any type
The variable in which to place the data read.
Discussion
The routine allows you to send and/or receive data from an I2C device. The specified channel must have
been previously opened with a call to OpenI2C(). If the channel has not been opened, the results are
undefined. If an invalid channel is specified or if both writeCnt and readCnt are zero, the function
returns immediately without doing anything and the return value is zero. You may specify the value 0 for
writeData or readData if no data is being provided for writing or reading, respectively. If you do this,
the corresponding data count parameter must also be zero or the compiler will issue an error message.
The execution of the I2C command sequence begins by issuing an I2C start condition on the SDA and
SCL lines. Next, if writeCnt is non-zero the given slaveID value is transmitted (with the least
significant bit being zero) followed by the specified number of bytes taken from writeData. Then, if
readCnt is non-zero the slaveID value is transmitted again but with the least significant bit being one
and the specified number of bytes is read from the slave and placed in readData. Finally, an I2C stop
condition is issued followed by both the SDA and SCL lines returning to the idle state.
The return value may be negative, zero or positive. If the return value is negative it signifies that the
slave failed to positively acknowledge one of the transmitted bytes. The value is the negative of the
number of bytes that were not successfully transmitted. If the slave fails to positively acknowledge either
the slave ID or the first data byte, the return value will be the negative of the writeCnt parameter value.
If the return value is non-negative it represents the number of data bytes read from the slave and placed
in readData.
Example
Dim odata(1 to 2) as Byte, idata(1 to 10) as Byte
Dim ival as Integer
Call OpenI2C (1, 12, 13)
odata(1) = &H06
odata(2) = &H00
ival = I2CCmd(1, &H7e, 2, odata(1), 10, idata(1))
Resource Usage
This function uses the I/O Timer for channels 1 to 4. If the timer is already in use, the result and the
return value are both undefined. Interrupts are disabled for periods of about 9 times the selected I2C bit
time plus additional amounts due to slave clock stretching for each byte sent and received (interrupts are
reenabled between bytes). However, RTC ticks are accumulated during the process so the RTC should
not lose time.
 |
 |
 |