ST72340 Datasheet, PDF (129/191 Pages) STMicroelectronics – 8-BIT MCU WITH UP TO 16K FLASH MEMORY, 10-BIT ADC, TWO 16-BIT TIMERS, TWO I2C, SPI, SCI

ST72340, ST72344, ST72345
I²C3S INTERFACE (Cont’d)
11.7.3 General Description
In addition to receiving and transmitting data,
I2C3S converts it from serial to parallel format and
vice versa. The interrupts are enabled or disabled
by software. The I2C3S is connected to the I²C
bus by a data pin (SDA) and by a clock pin (SCL).
It can be connected both with a standard I²C bus
and a Fast I²C bus. The interface operates only in
Slave mode as transmitter/receiver.
In order to fully emulate standard I²C EEPROM
devices with highest transfer speed, the peripheral
prevents I²C clock signal stretching and performs
data transfer between the shift register and the
RAM buffers using DMA.
11.7.3.1 Communication Flow
A serial data transfer normally begins with a start
condition and ends with a stop condition. Both
start and stop conditions are generated by an ex-
ternal master. Refer to Figure 64 for the standard
protocol. The I2C3S is not a master and is not ca-
pable of generating a start/stop condition on the
SDA line. The I2C3S is capable of recognising 3
Figure 69. I²C BUS Protocol
SDA
MSB
slave addresses which are user programmable.
The three I²C slave addresses can be individually
enabled/disabled by software.
Since the I2C3S interface always acts as a slave it
does not generate a clock. Data and addresses
are transferred as 8-bit bytes, MSB first. The first
byte following the start condition contains the
slave address. A 9th clock pulse follows the 8
clock cycles of a byte transfer, during which the re-
ceiver must send an acknowledge bit to the trans-
mitter.
11.7.3.2 SDA/SCL Line Control
When the I2C3S interface is enabled, the SDA and
SCL ports must be configured as floating inputs. In
this case, the value of the external pull-up resistor
used depends on the application.
When the I2C3S interface is disabled, the SDA
and SCL ports revert to being standard I/O port
pins.
ACK
SCL
1
2
8
9
START
CONDITION
STOP
CONDITION
VR02119B
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