Datasheet

21.3.1.5 Repeated Start
The I
2
C master module has the capability of executing a repeated START (transmit or receive) after
an initial transfer has occurred.
A repeated start sequence for a Master transmit is as follows:
1. When the device is in the idle state, the Master writes the slave address to the I2CMSA register
and configures the R/S bit for the desired transfer type.
2. Data is written to the I2CMDR register.
3. When the BUSY bit in the I2CMCS register is 0 , the Master writes 0x3 to the I2CMCS register
to initiate a transfer.
4. The Master does not generate a STOP condition but instead writes another slave address to
the I2CMSA register and then writes 0x3 to initiate the repeated START.
A repeated start sequence for a Master receive is similar:
1. When the device is in idle, the Master writes the slave address to the I2CMSA register and
configures the R/S bit for the desired transfer type.
2. The master reads data from the I2CMDR register.
3. When the BUSY bit in the I2CMCS register is 0 , the Master writes 0x3 to the I2CMCS register
to initiate a transfer.
4. The Master does not generate a STOP condition but instead writes another slave address to
the I2CMSA register and then writes 0x3 to initiate the repeated START.
For more information on repeated START, refer to Figure 21-12 on page 1443 and Figure
21-13 on page 1444.
21.3.1.6 Clock Low Timeout (CLTO)
The I
2
C slave can extend the transaction by pulling the clock low periodically to create a slow bit
transfer rate. The I
2
C module has a 12-bit programmable counter that is used to track how long the
clock has been held low. The upper 8 bits of the count value are software programmable through
the I
2
C Master Clock Low Timeout Count (I2CMCLKOCNT) register. The lower four bits are not
user visible and are 0x0. The CNTL value programmed in the I2CMCLKOCNT register has to be
greater than 0x01. The application can program the eight most significant bits of the counter to
reflect the acceptable cumulative low period in transaction. The count is loaded at the START
condition and counts down on each falling edge of the internal bus clock of the Master. Note that
the internal bus clock generated for this counter keeps running at the programmed I
2
C speed even
if SCL is held low on the bus. Upon reaching terminal count, the master state machine forces ABORT
on the bus by issuing a STOP condition at the instance of SCL and SDA release.
As an example, if an I
2
C module was operating at 100 kHz speed, programming the I2CMCLKOCNT
register to 0xDA would translate to the value 0xDA0 since the lower four bits are set to 0x0. This
would translate to a decimal value of 3488 clocks or a cumulative clock low period of 34.88 ms at
100 kHz.
The CLKRIS bit in the I
2
C Master Raw Interrupt Status (I2CMRIS) register is set when the clock
timeout period is reached, allowing the master to start corrective action to resolve the remote slave
state. In addition, the CLKTO bit in the I
2
C Master Control/Status (I2CMCS) register is set; this bit
December 13, 20131430
Texas Instruments-Advance Information
Inter-Integrated Circuit (I
2
C) Interface