Rev. 1.00
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Rev. 1.00
145
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HT66FM5440
Brushless DC Motor A/D Flash MCU
HT66FM5440
Brushless DC Motor A/D Flash MCU
Start
SET IICEN
Write Slave
Address to IICA
I
�
C B�s
Interr�pt=?
CLR IICE
Poll IICF to decide
when to go to I
�
C B�s ISR
SET IICE and Int_prinE
Wait for Interr�pt
Go to Main Program
Go to Main Program
Yes
No
Config�re the pin-shared I/O ports
to I
�
C f�nction
I
2
C Bus Initialisation Flow Chart
I
2
C Bus Start Signal
The START signal can only be generated by the master device connected to the I
2
C bus and not by the
slave device. This START signal will be detected by all devices connected to the I
2
C bus. When detected,
this indicates that the I
2
C bus is busy and therefore the HBB bit will be set. A START condition occurs
when a high to low transition on the SDA line takes place when the SCL line remains high.
I
2
C Slave Address
The transmission of a START signal by the master will be detected by all devices on the I
2
C bus.
To determine which slave device the master wishes to communicate with, the address of the slave
device will be sent out immediately following the START signal. All slave devices, after receiving
this 7-bit address data, will compare it with their own 7-bit slave address. If the address sent out by
the master matches the internal address of the microcontroller slave device, then an internal I
2
C bus
interrupt signal will be generated. The next bit following the address, which is the 8th bit, defines
the read/write status and will be saved to the SRW bit of the IICC1 register. The slave device will
then transmit an acknowledge bit, which is a low level, as the 9th bit. The slave device will also set
the status flag HAAS when the addresses match.
As an I
2
C bus interrupt can come from three sources, when the program enters the interrupt
subroutine, the HAAS and IICTOF bits should be examined to see whether the interrupt source has
come from a matching slave address or from the completion of a data byte transfer or the I
2
C time-
out occurrence. When a slave address is matched, the device must be placed in either the transmit
mode and then write data to the IICD register, or in the receive mode where it must implement a
dummy read from the IICD register to release the SCL line.
I
2
C Bus Read/Write Signal
The SRW bit in the IICC1 register defines whether the master device wishes to read data from the
I
2
C bus or write data to the I
2
C bus. The slave device should examine this bit to determine if it is to
be a transmitter or a receiver. If the SRW flag is "1" then this indicates that the master device wishes
to read data from the I
2
C bus, therefore the slave device must be setup to send data to the I
2
C bus as
a transmitter. If the SRW flag is "0" then this indicates that the master wishes to send data to the I
2
C
bus, therefore the slave device must be setup to read data from the I
2
C bus as a receiver.