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CHAPTER 13
SERIAL INTERFACE SIO0
User’s Manual U12790EJ2V0UD
13.4.7 Restrictions in using I2C bus mode
The following restrictions must be observed when using the
PD178078, 178098A Subseries.
 Restrictions when using as slave device in I2C bus mode
Devices:
PD178076, 178078, 178096A, 178098A, 178F098
IE-178098-NS-EM1
Description:
If the wakeup function is executed (by setting the WUP flag (bit 5 of serial operating
mode register 0 (CSIM0)) to 1) in the serial transfer statusNote, data between another
slave device and the master is identified as an address. If that data matches the slave
address of the
PD178078, 178098A Subseries, therefore, the PD178078, 178098A
Subseries participates in communication, destroying the communicated data.
Note The serial transfer status is the status after serial I/O shift register 0 (SIO0) has
been written until the interrupt request flag (CSIIF0) is set to 1 due to the end
of serial transfer.
Preventive measures:
The above problem can be avoided by modifying the program.
Before executing the wakeup function, execute the program shown below that clears
the serial transfer status.
When executing the wakeup function, do not write an
instruction that writes to SIO0. Data can be received during execution of the wake-
up function even if such an instruction is not executed.
This program clears the serial transfer status. To clear the serial transfer status, serial
interface SIO0 must be stopped once (by clearing the CSIE0 flag (bit 7 of serial
operating mode register 0 (CSIM0)) to 0). If serial interface SIO0 is stopped in the I2C
bus mode, however, the SCL pin outputs a high level and SDA0 (SDA1) pin outputs
a low level. Consequently, communication of the I2C bus may be affected. Therefore,
this program makes the SCL and SDA0 (SDA1) pins go into a high-impedance state
to prevent the I2C bus from being affected.
Note that, in this example, the SDA0 (/P25) pin is used as the serial data I/O pin.
If the SDA1 (/P26) pin is used as the serial data I/O pin, take P2.5 and PM2.5 in the
program below as P2.6 and PM2.6.
For the timing of each signal when this program is executed, refer to Figure 13-44.