Rev. 1.10
114
November 04, 2019
Rev. 1.10
115
November 04, 2019
HT45F5Q-3
Battery Charger Flash MCU
HT45F5Q-3
Battery Charger Flash MCU
Start
CLR UMD
SET SIM[2:0]=110
SET SIMEN
Write Slave
Address to SIMA
I
2
C Bus
Interrupt=?
CLR USIME
Poll USIMF to decide
when to go to I
2
C Bus ISR
SET USIME
Wait for Interrupt
Go to Main Program
Go to Main Program
Yes
No
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 USIM
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 SIMC1 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 USIM I
2
C bus interrupt can come from three sources, when the program enters the interrupt
subroutine, the HAAS and SIMTOF 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 from the
I
2
C bus 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 SIMD register, or in the receive mode where it must
implement a dummy read from the SIMD register to release the SCL line.
I
2
C Bus Read/Write Signal
The SRW bit in the SIMC1 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.