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CHAPTER 13
SERIAL INTERFACE SIO0
User’s Manual U12790EJ2V0UD
(10) Method used to judge busy state of a slave
When the device is in the master mode, use the method below to judge whether the slave device is in the
busy state or not.
<1> Detect acknowledge signal (ACK) or interrupt request signal generation.
<2> Set the port mode register PM25 (or PM26) of the SB0/P25 (or SB1/P26) pin to the input mode.
<3> Read out the pin state (when the pin level is high, the READY state is set).
After the detection of the READY state, set the port mode register to 0 and return to the output mode.
(11) SBI mode cautions
(a) Slave selection/non-selection is detected by match detection of the slave address received after bus
release (RELD = 1).
For this match detection, the match interrupt (INTCSI0) of the address generated with WUP = 1 is normally
used. Thus, execute selection/non-selection detection using the slave address when WUP = 1.
(b) When detecting selection/non-selection without using an interrupt with WUP = 0, do so by means of
transmission/reception of a command preset by the program instead of using the address match detection
method.
(c) In the SBI mode, SBI outputs the BUSY signal after the BUSY clear instruction has been executed until
the next serial clock falls. If WUP is set to 1 by mistake during this period, BUSY will not be cleared. Before
setting WUP to 1, therefore, clear BUSY, and make sure that the SB0 (SB1) pin has gone high.
(d) For pins which are to be used for data I/O, be sure to carry out the following settings before serial transfer
of the 1st byte after reset input.
<1> Set the P25 and P26 output latches to 1.
<2> Set bit 0 (RELT) of the serial bus control register to 1.
<3> Reset the P25 and P26 output latches from 1 to 0.
(e) A transition of the SB0 (SB1) pin from low to high or high to low is recognized as a bus release signal
or a command signal when the SCK0 line is high. If the change timing of the bus is shifted due to the
influence of board capacitance, data that is transmitted may be identified as a bus release signal or a
command signal by mistake. Exercise care when wiring.