
CHAPTER 17 I
2C BUS
User’s Manual U16541EJ4V0UD
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(3/4)
STTn
Start condition trigger
0
Start condition is not generated.
1
When bus is released (in STOP mode):
A start condition is generated (for starting as master). The SDA0n line is changed from high level to
low level while the SCLn line is high level and then the start condition is generated. Next, after the
rated amount of time has elapsed, the SCL0n line is changed to low level.
During communication with a third party:
If the communication reservation function is enabled (IICFn.IICRSVn bit = 0)
This trigger functions as a start condition reserve flag. When set to 1, it releases the bus and then
automatically generates a start condition.
If the communication reservation function is disabled (IICRSVn = 1)
The IICFn.STCFn bit is set to 1 and information set (1) to the STTn bit is cleared. This trigger
does not generate a start condition.
In the wait state (when master device):
A restart condition is generated after the wait state is released.
Cautions concerning set timing
For master reception:
Cannot be set to 1 during transfer. Can be set to 1 only when the ACKEn bit has been
set to 0 and the slave has been notified of final reception.
For master transmission: A start condition cannot be generated normally during the ACK period. Set to 1 during
the wait period that follows output of the ninth clock.
For slave:
Even when the communication reservation function is disabled (IICRSVn bit = 1), the
communication reservation status is entered.
Setting to 1 at the same time as the SPTn bit is prohibited.
When the STTn bit is set to 1, setting the STTn bit to 1 again is disabled until the setting is cleared to 0.
Condition for clearing (STTn bit = 0)
Condition for setting (STTn bit = 1)
When the STTn bit is set to 1 in the communication
reservation disabled status
Cleared by loss in arbitration
Cleared after start condition is generated by master
device
When the LRELn bit = 1 (communication save)
When the IICEn bit = 0 (operation stop)
After reset
Set by instruction
Remarks 1. The STTn bit is 0 if it is read immediately after data setting.
2. n = 0 to 2