R8C/1A Group, R8C/1B Group 16. Clock Synchronous Serial Interface
Rev.1.30 Dec 08, 2006 Page 179 of 315
REJ09B0252-0130
16.2.1 Transfer Clock
The transfer clock can be selected among seven internal clocks (f1/256, f1/128, f1/64, f1/32, f1/16, f1/8, and
f1/4) and an external clock.
When using clock synchronous serial I/O with chip select, set the SCKS bit in the SSMR2 register to 1 and
select the SSCK pin as the serial clock pin.
When the MSS bit in the SSCRH register is set to 1 (operates as master device), an internal clock can be
selected and the SSCK pin functions as output. When transfer is started, the SSCK pin outputs clocks of the
transfer rate selected by bits CKS0 to CKS2 in the SSCRH register.
When the MSS bit in the SSCRH register is set to 0 (operates as slave device), an external clock can be selected
and the SSCK pin functions as input.
16.2.1.1 Association between Transfer Clock Polarity, Phase, and Data
The association between the transfer clock polarity, phase and data changes according to the combination of the
SSUMS bit in the SSMR2 register and bits CPHS and CPOS in the SSMR register.
Figure 16.10 shows the Association between Transfer Clock Polarity, Phase, and Transfer Data.
Also, the MSB-first transfer or LSB-first transfer can be selected by setting the MLS bit in the SSMR register.
When the MLS bit is set to 1, transfer is started from the LSB and proceeds to the MSB. When the MLS bit is
set to 0, transfer is started from the MSB and proceeds to the LSB.
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