s908az32ag2cfue Freescale Semiconductor, Inc, s908az32ag2cfue Datasheet - Page 170

• Manufacturer Part Number: s908az32ag2cfue
• Description: M68hc08 Microcontrollers 8-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Serial Peirpheral Interface (SPI)
17.5.2 Transmission Format When CPHA = 0
Figure 17-4
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 logic 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
17.6.2 Mode Fault
the slave must begin driving its data before the first SPSCK edge, and a falling edge on the SS pin is used
to start the transmission. The SS pin must be toggled high and then low again between each byte
transmitted.
17.5.3 Transmission Format When CPHA = 1
Figure 17-5
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 logic 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
17.6.2 Mode Fault
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.
170
CAPTURE STROBE
FOR REFERENCE
FROM MASTER
SCK CPOL = 0
SCK CPOL = 1
SCK CYCLE #
FROM SLAVE
SS TO SLAVE
shows an SPI transmission in which CPHA (SPCR) is logic 0. The figure should not be used
shows an SPI transmission in which CPHA (SPCR) is logic 1. The figure should not be used
MOSI
MISO
Error). When CPHA = 0, the first SPSCK edge is the MSB capture strobe. Therefore,
Error). When CPHA = 1, the master begins driving its MOSI pin on the first SPSCK
MSB
Figure 17-4. Transmission Format (CPHA = 0)
MSB
1
MC68HC908AZ32A Data Sheet, Rev. 2
BIT 6
BIT 6
2
BIT 5
BIT 5
3
BIT 4
BIT 4
4
BIT 3
BIT 3
5
BIT 2
BIT 2
6
BIT 1
BIT 1
7
Freescale Semiconductor
LSB
LSB
8