NEC uPD78056Y - Manual (Page 378)

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CHAPTER 17 SERIAL INTERFACE CHANNEL 0 (
µ
PD78054Y Subseries)
(7) Error detection
In the I 2 C bus mode, transmission error detection can be performed by the following methods because the
serial bus SDA0 (SDA1) status during transmission is also taken into the serial I/O shift register 0 (SIO0)
register of the transmitting device.
(a) Comparison of SIO0 data before and after transmission
In this case, a transmission error is judged to have occurred if the two data values are different.
(b) Using the slave address register (SVA)
Transmit data is set in SIO0 and SVA before transmission is performed. After transmission, the COI bit (match
signal from the address comparator) of serial operating mode register 0 (CSIM0) is tested: "1" indicates normal
transmission, and "0" indicates a transmission error.
(8) Communication operation
In the I 2 C bus mode, the master selects the slave device to be communicated with from among multiple
devices by outputting address data onto the serial bus.
After the slave address data, the master sends the R/W bit which indicates the data transfer direction, and
starts serial communication with the selected slave device.
Data communication timing charts are shown in Figures 17-22 and 17-23.
In the transmitting device, the serial I/O shift register 0 (SIO0) shifts transmission data to the SO latch in
synchronization with the falling edge of the serial clock (SCL), the SO0 latch outputs the data on an MSB-
first basis from the SDA0 or SDA1 pin to the receiving device.
In the receiving device, the data input from the SDA0 or SDA1 pin is taken into the SIO0 in synchronization
with the rising edge of SCL.
(9) Start of transfer
A serial transfer is started by setting transfer data in serial I/O shift register 0 (SIO0) if the following two
conditions have been satisfied:
• The serial interface channel 0 operation control bit (CSIE0) = 1.
• After an 8-bit serial transfer, the internal serial clock is stopped or SCL is low.
Cautions 1. Be sure to set CSIE0 to 1 before writing data in SIO0. Setting CSIE0 to 1 after writing data
in SIO0 does not initiate transfer operation.
2. Because the N-ch open-drain output must be high-impedance state during data reception,
set bit 7 (BSYE) of serial bus interface control register (SBIC) to 1 before writing FFH to
SIO0.
Do not write FFH to SIO0 before reception when the wake-up function is used (by setting
the bit 5 (WUP) of the serial operating mode register 0 (CSIM0)). Even if FFH is not written
to SIO0, the N-ch open-drain output is always in high-impedance state.
3. If data is written to SIO0 while the slave is in the wait state, that data is held. The transfer
is started when SCL is output after the wait state is cleared.
When an 8-bit data transfer ends, serial transfer is stopped automatically and the interrupt request flag
(CSIIF0) is set.