MC68HC08AS32 Datasheet, PDF (283/394 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Serial Peripheral Interface (SPI)
Transmission Formats
18.6.2 Transmission Format When CPHA = 0
Figure 18-3 shows an SPI transmission in which CPHA (SPCR) is
logic 0. 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 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 18.7.2 Mode Fault Error.) When CPHA = 0, the first SPSCK
edge is the MSB capture strobe. Therefore, 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 as shown in Figure 18-4.
SCK CYCLE #
FOR REFERENCE
SCK CPOL = 0
SCK CPOL = 1
MOSI
FROM MASTER
MISO
FROM SLAVE
SS TO SLAVE
CAPTURE STROBE
1
2
3
4
5
6
7
8
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 18-3. Transmission Format (CPHA = 0)
MC68HC08AS32 — Rev. 3.0
MOTOROLA
Serial Peripheral Interface (SPI)
Advance Information
283