MC68HC08AZ0 Datasheet, PDF (229/444 Pages) Motorola, Inc – Advance Information

Freescale Semiconductor, Inc.
Serial Peripheral Interface Module (SPI)
Transmission formats
Transmission
format when
CPHA = Ô1Õ
Figure 6 shows an SPI transmission in which CPHA is ‘1’. The figure
should not be used as a replacement for data sheet parametric
information. Two waveforms are shown for SCK: one for CPOL = ‘0’ and
another for CPOL = ‘1’. The diagram may be interpreted as a master or
slave timing diagram since the serial clock (SCK), master in/slave out
(MISO), and master out/slave in (MOSI) pins are directly connected
between the master and the slave. The MISO signal is the output from
the slave, and the MOSI signal is the output from the master. The SS line
is the slave select input to the slave. The slave SPI drives its MISO
output only when its slave select input (SS) is at ‘0’, so that only the
selected slave drives to the master. The SS pin of the master is not
shown but is assumed to be inactive. The SS pin of the master must be
high or must be reconfigured as general-purpose I/O not affecting the
SPI. See Mode fault error on page 232. When CPHA = ‘1’, the master
begins driving its MOSI pin on the first SPSCK edge. Therefore the slave
uses the first SPSCK edge as a start transmission signal. The SS pin can
remain low between transmissions. This format may be preferable in
systems having only one master and only one slave driving the MISO
data line.
SCK CYCLE #
(FOR REFERENCE)
SCK (CPOL =’0’)
1
2
3
4
5
6
7
8
SCK (CPOL =1)
MOSI
(FROM MASTER)
MISO
(FROM SLAVE)
SS (TO SLAVE)
CAPTURE STROBE
MSB
BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1
LSB
MSB BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1
LSB
Figure 6. Transmission format (CPHA = ‘1’)
11-spi
MOTOROLA
Serial Peripheral Interface Module (SPI)
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MC68HC08AZ0
227