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CHAPTER 10 SERIAL INTERFACE FUNCTION
266
10.3.12 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 (LREL) of the IIC control register (IICC0) was set to “1”).
If bit 1 (STT) of IICC0 is set while the bus is not used a start condition is automatically generated and wait status is
set after the bus is released (after a stop condition is detected).
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 (SPIE) should be set.
When STT 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
To confirm the operation of communication reservation, set STT and check MSTS (bit 7 of IIC status register
(IICS0)) after the wait time.
Wait periods, which should be set via software, are listed in Table 10-6. These wait periods can be set via the
settings for bits 3, 1, and 0 (SMC, CL1, and CL0) in the IIC clock select register (IICCL0).
Table 10-6. Wait Periods
SMC
CL1
CL0
Wait Period
0
0
0
26 clocks
0
0
1
46 clocks
0
1
0
0
1
1
37 clocks
1
0
0
16 clocks
1
0
1
1
1
0
1
1
1
13 clocks
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