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RL78/G1A CHAPTER 13 SERIAL INTERFACE IICA
13.5.14 Communication reservation
(1) When communication reservation function is enabled (bit 0 (IICRSV) of IICA flag register 0 (IICF0) = 0)
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 by setting bit 6 (LREL0) of IICA control register 00 (IICCTL00) to 1 and saving communication).
If bit 1 (STT0) of the IICCTL00 register is set to 1 while the bus is not used (after a stop condition is detected), a
start condition is automatically generated and wait state is set.
If an address is written to the IICA shift register 0 (IICA0) after bit 4 (SPIE0) of the IICCTL00 register was set to 1,
and it was detected by generation of an interrupt request signal (INTIICA0) that the bus was released (detection of
the stop condition), then the device automatically starts communication as the master. Data written to the IICA0
register before the stop condition is detected is invalid.
When the STT0 bit has been set to 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 the MSTS0 bit (bit 7 of the IICA status
register 0 (IICS0)) after the STT0 bit is set to 1 and the wait time elapses.
Use software to secure the wait time calculated by the following expression.
Wait time from setting STT0 = 1 to checking the MSTS0 flag (number of clocks of f
MCK):
(IICWL0 setting value + IICWH0 setting value + 4) + t
F × 2 × fMCK [clocks]
Remark IICWL0: IICA low-level width setting register 0
IICWH0: IICA high-level width setting register 0
t
F: SDAA0 and SCLA0 signal falling times
fMCK: IICA operation clock frequency
R01UH0305EJ0200 Rev.2.00 604
Jul 04, 2013