HCS08 datasheet(197/290 Pages) MOTOROLA

197 / 290 page

Data Sheet — MC9S08GB60/D V1.5

MOTOROLA

197

MC9S08GB/GT

Figure 12-5 SPI Clock Formats (CPHA = 1)

When CPHA = 1, the slave begins to drive its MISO output when SS goes to active low, but the data is not

defined until the first SPSCK edge. The first SPSCK edge shifts the first bit of data from the shifter onto

the MOSI output of the master and the MISO output of the slave. The next SPSCK edge causes both the

master and the slave to sample the data bit values on their MISO and MOSI inputs, respectively. At the

third SPSCK edge, the SPI shifter shifts one bit position which shifts in the bit value that was just sampled,

and shifts the second data bit value out the other end of the shifter to the MOSI and MISO outputs of the

master and slave, respectively. When CHPA = 1, the slave’s SS input is not required to go to its inactive

high level between transfers.

Figure 12-6 shows the clock formats when CPHA = 0. At the top of the figure, the eight bit times are

shown for reference with bit 1 starting as the slave is selected (SS IN goes low), and bit 8 ends at the last

SPSCK edge. The MSB first and LSB first lines show the order of SPI data bits depending on the setting

in LSBFE. Both variations of SPSCK polarity are shown, but only one of these waveforms applies for a

specific transfer, depending on the value in CPOL. The SAMPLE IN waveform applies to the MOSI input

of a slave or the MISO input of a master. The MOSI waveform applies to the MOSI output pin from a

master and the MISO waveform applies to the MISO output from a slave. The SS OUT waveform applies

to the slave select output from a master (provided MODFEN and SSOE = 1). The master SS output goes

to active low at the start of the first bit time of the transfer and goes back high one-half SPSCK cycle after

the end of the eighth bit time of the transfer. The SS IN waveform applies to the slave select input of a

slave.

BIT TIME #

(REFERENCE)

MSB FIRST

LSB FIRST

SPSCK

(CPOL = 0)

SPSCK

(CPOL = 1)

SAMPLE IN

(MISO OR MOSI)

MOSI

(MASTER OUT)

MISO

(SLAVE OUT)

SS OUT

(MASTER)

SS IN

(SLAVE)

BIT 7

BIT 0

BIT 6

BIT 1

BIT 2

BIT 5

BIT 1

BIT 6

BIT 0

BIT 7

...

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