MC97F2664
April 11, 2014 Ver. 1.4
191
Figure 11.47 USI0/1 SPI Clock Formats when CPHAn=0 (where n = 0 and 1)
When CPHAn=0, the slave begins to drive its MISOn output with the first data bit value when SSn goes to active
low. The first SCKn edge causes both the master and the slave to sample the data bit value on their MISOn and
MOSIn inputs, respectively. At the second SCKn edge, the USI0/1 shifts the second data bit value out to the
MOSIn and MISOn outputs of the master and slave, respectively. Unlike the case of CPHAn=1, when CPHAn=0,
the slave’s SSn input must go to its inactive high level between transfers. This is because the slave can prepare
the first data bit when it detects falling edge of SSn input.
SCKn
(CPOLn=1)
MISOn
MOSIn
SCKn
(CPOLn=0)
/SSn OUT
(MASTER)
BIT7
BIT0
/SSn IN
(SLAVE)
BIT6
BIT1
…
…
BIT2
BIT5
BIT0
BIT7
BIT1
BIT6
SAMPLE
MSB First
LSB First
Содержание MC97F2664
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