Abov MC96F6332D, User Manual

Page: 253 / 327

MC96F6432
June 22, 2018 Ver. 2.9 253
11.13.20.2 USI1 I2C Master Receiver
To operate I2C in master receiver, follow the recommended steps below.
1. Enable I2C by setting USI1MS[1:0] bits in USI1CR1 and USI1EN bit in USI1CR2. This provides main
clock to the peripheral.
2. Load SLA1+R into the USI1DR where SLA is address of slave device and R is transfer direction from
the viewpoint of the master. For master receiver, R is
‘1’. Note that USI1DR is used for both address
and data.
3. Configure baud rate by writing desired value to both USI1SCLR and USI1SCHR for the Low and High
period of SCL1 line.
4. Configure the USI1SDHR to decide when SDA1 changes value from falling edge of SCL1. If SDA1
should change in the middle of SCL1 LOW period, load half the value of USI1SCLR to the USI1SDHR.
5. Set the STARTC1 bit in USI1CR4. This transmits a START condition. And also configure how to handle
interrupt and ACK signal. When the STARTC1 bit is set, 8-bit data in USI1DR is transmitted out
according to the baud-rate.
6. This is ACK signal processing stage for address packet transmitted by master. When 7-bit address and
1-bit transfer direction is transmitted to target slave device, the master can know whether the slave
acknowledged or not in the 9
th
high period of SCL1. If the master gains bus mastership, I2C generates
GCALL interrupt regardless of the reception of ACK from the slave device. When I2C loses bus
mastership during arbitration process, the MLOST1 bit in USI1ST2 is set, and I2C waits in idle state or
can be operate as an addressed slave. To operate as a slave when the MLOST1 bit in USI1ST2 is set,
the ACK1EN bit in USI1CR4 must be set and the received 7-bit address must equal to the USI1SLA[6:0]
bits in USI1SAR. In this case I2C operates as a slave transmitter or a slave receiver (go to appropriate
section). In this stage, I2C holds the SCL1 LOW. This is because to decide whether I2C continues serial
transfer or stops communication. The following steps continue assuming that I2C does not lose
mastership during first data transfer.
I2C (Master) can choose one of the following cases according to the reception of ACK signal from slave.
1) Master receives ACK signal from slave, so continues data transfer because slave can prepare and
transmit more data to master. Configure ACK0EN bit in USI0CR4 to decide whether I2C ACKnowledges
the next data to be received or not.
2) Master stops data transfer because it receives no ACK signal from slave. In this case, set the
STOPC1 bit in USI1CR4.
3) Master transmits repeated START condition due to no ACK signal from slave. In this case, load
SLA1+R/W into the USI1DR and set STARTC1 bit in USI1CR4.
After doing one of the actions above, clear to
“0b” all interrupt source bits in USI1ST2 to release SCL1
line. In case of 1), move to step 7. In case of 2), move to step 9 to handle STOP interrupt. In case of 3),
move to step 6 after transmitting the data in USI1DR and if transfer direction bit is
‘0’ go to master
transmitter section.
7. 1-Byte of data is being received.
8. This is ACK signal processing stage for data packet transmitted by slave. I2C holds the SCL1 LOW.
When 1-Byte of data is received completely, I2C generates TEND1 interrupt.
I2C can choose one of the following cases according to the RXACK1 flag in USI1ST2.
1) Master continues receiving data from slave. To do this, set ACK1EN bit in USI0CR4 to ACKnowledge
the next data to be received.
2) Master wants to terminate data transfer when it receives next data by not generating ACK signal. This
can be done by clearing ACK1EN bit in USI1CR4.
3) Because no ACK signal is detected, master terminates data transfer. In this case, set the STOPC1 bit
in USI1CR4.
4) No ACK signal is detected, and master transmits repeated START condition. In this case, load
SLA1+R/W into the USI1DR and set the STARTC1 bit in USI1CR4.
After doing one of the actions above, clear to
“0b” all interrupt source bits in USI1ST2 to release SCL1
line. In case of 1) and 2), move to step 7. In case of 3), move to step 9 to handle STOP interrupt. In case
of 4), move to step 6 after transmitting the data in USI1DR, and if transfer direction bit is
‘0’ go to master
transmitter section.