Renesas RL78/G1P Hardware User Manual page 520

RL78/G1P
12.5.14 Communication reservation
(1) When communication reservation function is enabled (bit n (IICRSVn) of IICA flag register n (IICFn) = 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 (LRELn) of IICA control register n0 (IICCTLn0) to 1 and saving communication).
If bit 1 (STTn) of the IICCTLn0 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 n (IICAn) after bit 4 (SPIEn) of the IICCTLn0 register was set to 1,
and it was detected by generation of an interrupt request signal (INTIICAn) that the bus was released (detection of
the stop condition), then the device automatically starts communication as the master. Data written to the IICAn
register before the stop condition is detected is invalid.
When the STTn 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 MSTSn bit (bit 7 of the IICA status
register n (IICSn)) after the STTn 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 STTn = 1 to checking the MSTSn flag:
(IICWLn setting value + IICWHn setting value + 4) + t
Remarks 1. IICWLn:
2. n = 0, 1
R01UH0895EJ0100 Rev.1.00
Nov 29, 2019
IICA low-level width setting register n
IICWHn: IICA high-level width setting register n
t : SDAAn and SCLAn signal falling times
F
f : CPU/peripheral hardware clock frequency
CLK
CHAPTER 12 SERIAL INTERFACE IICA
 2  f
[clocks]
F CLK
501