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10.3.12 Communication reservation
To start master device communications when not currently using the 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 (LRELn) of IIC control register n (IICCn) was set to 1) (n = 0, 1).
If bit 1 (STTn) of IICCn is set while the bus is not used, a start condition is automatically generated and a 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 IIC shift register n (IICn) causes
the master's address transfer to start. At this point, bit 4 (SPIEn) of IICCn should be set (n = 0, 1).
When STTn has been set, the operation mode (as start condition or as communication reservation) is determined
according to the bus status (n = 0, 1).
If the bus has been released ............................................. a start condition is generated
If the bus has not been released (standby mode) ............. communication reservation
To detect which operation mode has been determined for STTn, set STTn, wait for the wait period, then check the
MSTSn (bit 7 of IIC status register n (IICSn)) (n = 0, 1).
Wait periods, which should be set via software, are listed in Table 10-7. These wait periods can be set via the
settings for bits 3, 1, and 0 (SMCn, CLn1, and CLn0) of IIC clock selection register n (IICCLn) (n = 0, 1).
Remark
CHAPTER 10
SERIAL INTERFACE FUNCTION
Table 10-7. Wait Periods
SMCn
CLn1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
n = 0, 1
User's Manual U13850EJ6V0UD
CLn0
Wait Period
0
26 clocks
1
46 clocks
0
92 clocks
1
37 clocks
0
16 clocks
1
0
32 clocks
1
13 clocks
321
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