R01UH0136EJ0210 Rev.2.10
Page 579 of 800
Jul 31, 2012
M16C/64A Group
25. Multi-master I
2
C-bus Interface
25.5
Notes on Multi-master I
2
C-bus Interface
25.5.1
Limitation on CPU Clock
When the CM07 bit in the CM0 register is 1 (CPU clock is a sub clock), do not access the registers
listed in Table 25.4 “Registers”. Set the CM07 bit to 0 (main clock, PLL clock, or on-chip oscillator clock)
to access these registers.
25.5.2
Register Access
Refer to the notes below when accessing the I
2
C interface control registers. The period from the rising
edge of the first clock of the slave address or 1-byte data transmission/reception to the falling edge of
an ACK clock is considered to be the transmission/reception period. When the ACKCLK bit is 0 (no
ACK clock), the transmission/reception period is from the rising edge of the first clock of the slave
address or 1-byte data transmission/reception to the falling edge of the eighth clock.
25.5.2.1
S00 Register
Do not write to the S00 register during transmission/reception.
25.5.2.2
S1D0 Register
Do not change bits other than the IHR bit in the S1D0 register during transmission/reception.
25.5.2.3
S20 Register
Do not change bits other than the ACKBIT bit in the S20 register during transmission/reception.
25.5.2.4
S3D0 Register
• Do not use the bit managing instruction (read-modify-write instruction) to access the S3D0 register.
Use the MOV instruction to write to this register.
• Rewrite bits ICK1 and ICK0 when the ES0 bit in the S1D0 register is 0 (I
2
C interface disabled).
25.5.2.5
S4D0 Register
Rewrite bits ICK4 to ICK2 when the ES0 bit in the S1D0 register is 0 (I
2
C interface disabled).
25.5.2.6
S10 Register
•
Do not use the bit managing instruction (read-modify-write instruction) to access the S10 register.
Use the MOV instruction to write to this register.
•
Do not write to the S10 register when bits MST and TRX change their values.
Refer to operation examples in 25.3 “Operations”
for bits MST and TRX change.
25.5.3
Low/High-level Input Voltage and Low-level Output Voltage
The low-level input voltage, high-level input voltage, and low-level output voltage differ from the I
2
C-bus
specification.
Refer to the recommended operating conditions for I/O ports which share the pins with SCL and SDA.
I
2
C-bus specification
High level input voltage (V
IH
) = min. 0.7 V
CC
Low level input voltage (V
IL
) = max. 0.3 V
CC
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