ST72521 STMICROELECTRONICS [STMicroelectronics], ST72521 Datasheet - Page 117

• Manufacturer Part Number: ST72521
• Description: 8-BIT MCU WITH NESTED INTERRUPTS, FLASH, 10-BIT ADC, FIVE TIMERS, SPI, SCI, I2C, CAN INTERFACE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

I
How to release the SDA / SCL lines
Set and subsequently clear the STOP bit while
BTF is set. The SDA/SCL lines are released after
the transfer of the current byte.
10.7.4.2 Master Mode
To switch from default Slave mode to Master
mode a Start condition generation is needed.
Start condition
Setting the START bit while the BUSY bit is
cleared causes the interface to switch to Master
mode (M/SL bit set) and generates a Start condi-
tion.
Once the Start condition is sent:
– The EVF and SB bits are set by hardware with
Then the master waits for a read of the SR1 regis-
ter followed by a write in the DR register with the
Slave address, holding the SCL line low (see
Figure 65
Slave address transmission
Then the slave address is sent to the SDA line via
the internal shift register.
In 7-bit addressing mode, one address byte is
sent.
In 10-bit addressing mode, sending the first byte
including the header sequence causes the follow-
ing event:
– The EVF bit is set by hardware with interrupt
Then the master waits for a read of the SR1 regis-
ter followed by a write in the DR register, holding
the SCL line low (see
quencing EV9).
Then the second address byte is sent by the inter-
face.
2
C BUS INTERFACE (Cont’d)
an interrupt if the ITE bit is set.
generation if the ITE bit is set.
Transfer sequencing EV5).
Figure 65
Transfer se-
After completion of this transfer (and acknowledge
from the slave if the ACK bit is set):
– The EVF bit is set by hardware with interrupt
Then the master waits for a read of the SR1 regis-
ter followed by a write in the CR register (for exam-
ple set PE bit), holding the SCL line low (see
ure 65
Next the master must enter Receiver or Transmit-
ter mode.
Note: In 10-bit addressing mode, to switch the
master to Receiver mode, software must generate
a repeated Start condition and resend the header
sequence with the least significant bit set
(11110xx1).
Master Receiver
Following the address transmission and after SR1
and CR registers have been accessed, the master
receives bytes from the SDA line into the DR reg-
ister via the internal shift register. After each byte
the interface generates in sequence:
– Acknowledge pulse if if the ACK bit is set
– EVF and BTF bits are set by hardware with an in-
Then the interface waits for a read of the SR1 reg-
ister followed by a read of the DR register, holding
the SCL line low (see
quencing EV7).
To close the communication: before reading the
last byte from the DR register, set the STOP bit to
generate the Stop condition. The interface goes
automatically back to slave mode (M/SL bit
cleared).
Note: In order to generate the non-acknowledge
pulse after the last received data byte, the ACK bit
must be cleared just before reading the second
last data byte.
generation if the ITE bit is set.
terrupt if the ITE bit is set.
Transfer sequencing EV6).
Figure 65
Transfer se-
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