CHAPTER 17 SERIAL INTERFACE IIC0 (
µ
PD780344Y, 780354Y SUBSERIES ONLY)
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User’s Manual U15798EJ2V0UD
17.5.14 Communication reservation
To start master device communications when not currently using a bus, a communication reservation can be made
to enable transmission of a start condition when the bus is released. There are two modes under which the bus is
not used.
• When arbitration results in neither master nor slave operation
• When an extension code is received and slave operation is disabled (ACK is not returned and the bus was
released when bit 6 (LREL0) of IIC control register 0 (IICC0) was set to 1).
If bit 1 (STT0) of IICC0 is set (1) while the bus is not being used, a start condition is automatically generated and
the wait status is set after the bus is released (when a stop condition is detected).
When the bus release is detected (when a stop condition is detected), writing to IIC shift register 0 (IIC0) causes
the master’s address transfer to start. At this point, IICC0’s bit 4 (SPIE0) should be set (1).
When STT0 has been set (1), the operation mode (as start condition or as communication reservation) is determined
according to the bus status.
• If the bus has been released ........................................... A start condition is generated
• If the bus has not been released (standby mode) .......... Communication reservation
Check whether the communication reservation operates or not using MSTS0 (bit 7 of IIC status register 0 (IICS0))
after STT0 is set and the wait time elapses.
Wait periods, which should be set via software, are listed in Table 17-5. These wait periods can be set via the
settings of bits 3 and 0 (SMC0 and CL00) of IIC transfer clock select register 0 (IICCL0).
Table 17-5. Wait Periods
SMC0
CL00
Wait Period
0
0
26 clocks
0
1
46 clocks
1
0
16 clocks
1
1
Figure 17-16 shows communication reservation timing.
