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CHAPTER 18 SERIAL INTERFACE (IIC0) (
μ
PD780024Y, 780034Y SUBSERIES ONLY)
18.5.14 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 the IIC control register (IICC0) was set to “1”).
If bit 1 (STT0) of IICC0 is set while the bus is not used (after a stop condition is detected), a start condition is
automatically generated and wait status is set.
When the bus release is detected (when a stop condition is detected), writing to the IIC shift register (IIC0) causes
the master’s address transfer to start. At this point, IICC0’s bit 4 (SPIE0) should be set.
When STT0 has been set, 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 with MSTS0 (bit 7 of the IIC status register (IICS0))
after SST0 is set and a wait time elapses.
Wait periods, which should be set via software, are listed in Table 18-5. These wait periods can be set via the
settings for bits 3 and 0 (SMC0 and CL00) in the IIC clock select register (IICCL0).
Table 18-5. Wait Periods
SMC0
CL00
Wait period
0
0
26 clocks
0
1
46 clocks
1
0
16 clocks
1
1
Figure 18-5 shows communication reservation timing.