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359
CHAPTER 18 SERIAL INTERFACE IIC0 (
μ
PD780078Y SUBSERIES ONLY)
User
’
s Manual U14260EJ3V1UD
18.5.13 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 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 IIC shift register 0 (IIC0) causes the master address transfer to start. At this point, bit 4 (SPIE0) of IICC0
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 by using MSTS0 (bit 7 of IIC status register 0 (IICS0))
after SST0 is set and the wait time elapses.
The 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 IIC transfer clock select register 0 (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 18-18 shows the communication reservation timing.