MC68HC812A4 Datasheet, PDF (269/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Serial Peripheral Interface (SPI)
Functional Description
NOTE: To transmit between SPI modules, both modules must have identical
CPHA and CPOL values.
When CPHA = 0, a falling SS edge signals the slave to begin
transmission. The capture strobe for the first bit occurs on the first serial
clock edge. Therefore, the slave must begin driving its data before the
first serial clock edge. After transmission of all eight bits, the slave SS
pin must toggle from low to high to low again to begin another
transmission. This format may be preferable in systems having more
than one slave driving the master MISO line.
BEGIN
TRANSFER
t_L
END
TRANSFER
SCK CYCLES
1
2
3
4
5
6
7
8
SCK
CPOL = 0
SCK
CPOL = 1
MOSI
FROM MASTER
MISO
FROM SLAVE
SS
TO SLAVE
CAPTURE STROBE
MSB FIRST (LSBF = 0) MSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
LSB
LSB FIRST (LSBF = 1) LSB
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
MSB
MINIMUM t_L, t_T, and t_I = 1/2 SCK CYCLE
Figure 15-4. Transmission Format 0 (CPHA = 0)
t_T
t_I
MISO/MOSI
BYTE 1
BYTE 2
BYTE 3
MASTER SS
SLAVE SS
CPHA = 0
Figure 15-5. Slave SS Toggling When CPHA = 0
Advance Information
MOTOROLA
Serial Peripheral Interface (SPI)
MC68HC812A4 — Rev. 3.0
269