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R8C/14 Group, R8C/15 Group 15. Clock Synchronous Serial I/O with Chip Select (SSU)
Rev.2.10 Jan 19, 2006 Page 161 of 253
REJ09B0164-0210
15.6 Operation in 4-Wire Bus Communication Mode
4-wire bus communication mode is a mode which communicates with the 4-wire bus; a clock line, data
input line, data output line and chip select line. 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 are changed according to the setting of the MSS bit in the SSCRH
register and the BIDE bit in the SSMR2 register. For details, refer to
15.2.1 Association between Data
I/O Pin and SS Shift Register
. In this mode, association between the clock polarity, phase and data can
be set by the CPOS and CPHS bits in the SSMR register. For details, refer to
15.1.1 Association
between Transfer Clock Polarity, Phase and Data
.
When the SSU is set as a master device, the chip select line controls output. When the SSU is set as a
slave device, the chip select line controls input. When the SSU is set as master device, the chip select
line controls output of the SCS
pin or controls output of a general port by setting the CSS1 bit in the
SSMR2 register. When the SSU is set as a slave device, the chip select line set the SCS
pin as an input
pin by setting the CSS1 and CSS0 bits 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 using the MSB-first.
15.6.1 Initialization in 4-Wire Bus Communication Mode
Figure 15.17 shows an Initialization in 4-Wire Bus Communication Mode. Before the data transit/
receive, set the TE bit in the SSER register to “0” (disables transmit) and the RE bit in the SSER
register to “0” (disables receive) and initialize the SSU.
When communication mode and format are changed, set the TE bit to “0” and the RE bit to “0” before
changing.
Setting the RE bit to “0” does not change the contents of the RDRF and ORER flags, and the contents
of the SSRDR register.
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