R8C/1A Group, R8C/1B Group
16. Clock Synchronous Serial Interface
Rev.1.30
Dec 08, 2006
Page 191 of 315
REJ09B0252-0130
16.2.6
Operation in 4-Wire Bus Communication Mode
In 4-wire bus communication mode, a 4-wire bus consisting of a clock line, a data input line, a data output line,
and a chip select line is used for communication. This mode includes bidirectional mode in which the data input
line and data output line function as a single pin.
The data input line and output line change according to the settings of the MSS bit in the SSCRH register and
the BIDE bit in the SSMR2 register. For details, refer to
16.2.2.1 Association between Data I/O Pins and SS
Shift Register
. In this mode, clock polarity, phase, and data settings are performed by bits CPOS and CPHS in
the SSMR register. For details, refer to
16.2.1.1 Association between Transfer Clock Polarity, Phase, and
Data
.
When this MCU is set as the master device, the chip select line controls output. When clock synchronous serial
I/O with chip select is set as a slave device, the chip select line controls input. When it is set as the master
device, the chip select line controls output of the SCS pin or controls output of a general port according to the
setting of the CSS1 bit in the SSMR2 register. When the MCU is set as a slave device, the chip select line sets
the SCS pin as an input pin by setting bits CSS1 and CSS0 in the SSMR2 register to 01b.
In 4-wire bus communication mode, the MLS bit in the SSMR register is set to 0 and communication is
performed MSB-first.
16.2.6.1
Initialization in 4-Wire Bus Communication Mode
Figure 16.18 shows Initialization in 4-Wire Bus Communication Mode. Before the data transit/receive
operation, set the TE bit in the SSER register to 0 (transmit disabled), the RE bit in the SSER register to 0
(receive disabled), and initialize the clock synchronous serial I/O with chip select.
To change the communication mode or format, set the TE bit to 0 and the RE bit to 0 before making the change.
Setting the RE bit to 0 does not change the settings of flags RDRF and ORER or the contents of the SSRDR
register.
