ST72321AR7 STMicroelectronics, ST72321AR7 Datasheet - Page 117

• Manufacturer Part Number: ST72321AR7
• Description: 8-BIT MCU WITH NESTED INTERRUPTS, FLASH,10-BIT ADC, FIVE TIMERS, SPI, SCI, I2C INTERFACE
• Manufacturer: STMicroelectronics

Specifications of ST72321AR7

• Hdflash Endurance: 100 cycles, data retention
• Clock Sources: crystal/ceramic resonator oscillators, internal RC oscillator, clock security system and bypass for external clock
• Four Power Saving Modes: Halt, Active-Halt,Wait and Slow
• Main Clock Controller With: Real time base, Beep and Clock-out capabilities
• Two 16-bit Timers With: 2 input captures, 2 output compares, external clock input on one timer, PWM and pulse generator modes
• 8-bit Pwm Auto-reload Timer With: 2 input captures, 4 PWM outputs, output compare and time base interrupt, external clock with event detector

I
10.7.4 Functional Description
Refer to the CR, SR1 and SR2 registers in
10.7.7. for the bit definitions.
By default the I
mode (M/SL bit is cleared) except when it initiates
a transmit or receive sequence.
First the interface frequency must be configured
using the FRi bits in the OAR2 register.
10.7.4.1 Slave Mode
As soon as a start condition is detected, the
address is received from the SDA line and sent to
the shift register; then it is compared with the
address of the interface or the General Call
address (if selected by software).
Note: In 10-bit addressing mode, the comparison
includes the header sequence (11110xx0) and the
two most significant bits of the address.
Header matched (10-bit mode only): the interface
generates an acknowledge pulse if the ACK bit is
set.
Address not matched: the interface ignores it
and waits for another Start condition.
Address matched: the interface generates in se-
quence:
– Acknowledge pulse if the ACK bit is set.
– EVF and ADSL bits are set with an interrupt if the
Then the interface waits for a read of the SR1 reg-
ister, holding the SCL line low (see
Transfer sequencing EV1).
Next, in 7-bit mode read the DR register to deter-
mine from the least significant bit (Data Direction
Bit) if the slave must enter Receiver or Transmitter
mode.
In 10-bit mode, after receiving the address se-
quence the slave is always in receive mode. It will
enter transmit mode on receiving a repeated Start
condition followed by the header sequence with
matching address bits and the least significant bit
set (11110xx1).
Slave Receiver
Following the address reception and after SR1
register has been read, the slave receives bytes
from the SDA line into the DR register via the inter-
nal shift register. After each byte the interface gen-
erates in sequence:
– Acknowledge pulse if the ACK bit is set
– EVF and BTF bits are set with an interrupt if the
2
C BUS INTERFACE (Cont’d)
ITE bit is set.
ITE bit is set.
2
C interface operates in Slave
Figure 66
Section
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 EV2).
Slave Transmitter
Following the address reception and after SR1
register has been read, the slave sends bytes from
the DR register to the SDA line via the internal shift
register.
The slave waits for a read of the SR1 register fol-
lowed by a write in the DR register, holding the
SCL line low (see
EV3).
When the acknowledge pulse is received:
– The EVF and BTF bits are set by hardware with
Closing slave communication
After the last data byte is transferred a Stop Con-
dition is generated by the master. The interface
detects this condition and sets:
– EVF and STOPF bits with an interrupt if the ITE
Then the interface waits for a read of the SR2 reg-
ister (see
Error Cases
– BERR: Detection of a Stop or a Start condition
– AF: Detection of a non-acknowledge bit. In this
Note: In case of errors, SCL line is not held low;
however, the SDA line can remain low if the last
bits transmitted are all 0. While AF=1, the SCL line
may be held low due to SB or BTF flags that are
set at the same time. It is then necessary to re-
lease both lines by software.
an interrupt if the ITE bit is set.
bit is set.
during a byte transfer. In this case, the EVF and
the BERR bits are set with an interrupt if the ITE
bit is set.
If it is a Stop then the interface discards the data,
released the lines and waits for another Start
condition.
If it is a Start then the interface discards the data
and waits for the next slave address on the bus.
case, the EVF and AF bits are set with an inter-
rupt if the ITE bit is set.
The AF bit is cleared by reading the I2CSR2 reg-
ister. However, if read before the completion of
the transmission, the AF flag will be set again,
thus possibly generating a new interrupt. Soft-
ware must ensure either that the SCL line is back
at 0 before reading the SR2 register, or be able
to correctly handle a second interrupt during the
9th pulse of a transmitted byte.
ST72321Rx ST72321ARx ST72321Jx
Figure 66
Figure 66
Transfer sequencing EV4).
Figure 66
Transfer sequencing
Transfer se-
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