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CHAPTER 16 SERIAL INTERFACE IICA
User’s Manual U19780EJ2V0UD
432
Figure 16-5. Format of IICA Control Register 0 (IICACTL0) (3/4)
STT0
Note
Start condition trigger
0
Do not generate a start condition.
1
When bus is released (in stop state):
Generate a start condition (for starting as master). When the SCLA0 line is high level, the SDAA0 line
is changed from high level to low level and then the start condition is generated. Next, after the rated
amount of time has elapsed, SCLA0 is changed to low level (wait state).
When a third party is communicating:
•
When communication reservation function is enabled (IICRSV = 0)
Functions as the start condition reservation flag. When set to 1, automatically generates a start
condition after the bus is released.
•
When communication reservation function is disabled (IICRSV = 1)
STCF is set to 1 and information that is set (1) to STT0 is cleared. No start condition is generated.
In the wait state (when master device):
Generates a restart condition after releasing the wait.
Cautions concerning set timing
•
For master reception:
Cannot be set to 1 during transfer. Can be set to 1 only in the waiting period when
ACKE0 has been cleared to 0 and slave has been notified of final reception.
•
For master transmission: A start condition cannot be generated normally during the acknowledge period. Set to 1
during the wait period that follows output of the ninth clock.
•
Cannot be set to 1 at the same time as SPT0.
•
Setting STT0 to 1 and then setting it again before it is cleared to 0 is prohibited.
Condition for clearing (STT0 = 0)
Condition for setting (STT0 = 1)
•
Cleared by setting STT0 to 1 while communication
reservation is prohibited.
•
Cleared by loss in arbitration
•
Cleared after start condition is generated by master
device
•
Cleared by LREL0 = 1 (exit from communications)
•
When IICE0 = 0 (operation stop)
•
Reset
•
Set by instruction
Note
The signal of this bit is invalid while IICE0 is 0.
Remarks 1.
Bit 1 (STT0) becomes 0 when it is read after data setting.
2.
IICRSV: Bit 0 of IICA flag register (IICAF0)
STCF: Bit 7 of IICA flag register (IICAF0)