参数资料
型号: ST72P63BE4M1
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDSO24
封装: 0.300 INCH, ROHS COMPLIANT, PLASTIC, SOP-24
文件页数: 133/145页
文件大小: 2984K
代理商: ST72P63BE4M1
ST7263BDx ST7263BHx ST7263BKx ST7263BE
88/145
IC bus interface (Cont’d)
12.5.4 Functional description
Refer to the CR, SR1 and SR2 registers in Section
12.5.7. for the bit definitions.
By default the IC interface operates in Slave
mode (M/SL bit is cleared) except when it initiates
a transmit or receive sequence.
12.5.4.1 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).
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
ITE bit is set.
Then the interface waits for a read of the SR1 reg-
ister, holding the SCL line low (see Figure 45
Transfer sequencing EV1).
Next, software must read the DR register to deter-
mine from the least significant bit (Data Direction
Bit) if the slave must enter Receiver or Transmitter
mode.
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
ITE bit is set.
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 Figure 45 Transfer se-
quencing EV2).
Slave transmitter
Following the address reception and after the 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 Figure 45 Transfer sequencing
EV3).
When the acknowledge pulse is received:
– The EVF and BTF bits are set by hardware with
an interrupt if the ITE bit is set.
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
bit is set.
Then the interface waits for a read of the SR2 reg-
ister (see Figure 45 Transfer sequencing EV4).
Error cases
– BERR: Detection of a Stop or a Start condition
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.
– AF: Detection of a non-acknowledge bit. In this
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.
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.
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.
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