ST72321B STMICROELECTRONICS [STMicroelectronics], ST72321B Datasheet - Page 92

• Manufacturer Part Number: ST72321B
• Description: 64/44-pin 8-bit MCU with 32 to 60K Flash/ROM, ADC, five timers, SPI, SCI, I2C interface
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

SERIAL PERIPHERAL INTERFACE (Cont’d)
10.5.4 Clock Phase and Clock Polarity
Four possible timing relationships may be chosen
by software, using the CPOL and CPHA bits (See
Figure
Note: The idle state of SCK must correspond to
the polarity selected in the SPICSR register (by
pulling up SCK if CPOL=1 or pulling down SCK if
CPOL=0).
The combination of the CPOL clock polarity and
CPHA (clock phase) bits selects the data capture
clock edge
Figure 58. Data Clock Timing Diagram
92/187
(from slave)
(from slave)
58).
(to slave)
(to slave)
(from master)
(from master)
SCK
(CPOL = 0)
MISO
MOSI
CAPTURE STROBE
SCK
(CPOL = 1)
SCK
(CPOL = 0)
MISO
MOSI
CAPTURE STROBE
SCK
(CPOL = 1)
SS
SS
Note: This figure should not be used as a replacement for parametric information.
Refer to the Electrical Characteristics chapter.
MSBit
MSBit
MSBit
MSBit
Bit 6
Bit 6
Bit 6
Bit 6
Bit 5
Bit 5
Bit 5
Bit 5
CPHA =0
CPHA =1
Bit 4
Bit 4
Bit 4
Bit 4
Figure
combinations of the CPHA and CPOL bits. The di-
agram may be interpreted as a master or slave
timing diagram where the SCK pin, the MISO pin,
the MOSI pin are directly connected between the
master and the slave device.
Note: If CPOL is changed at the communication
byte boundaries, the SPI must be disabled by re-
setting the SPE bit.
Bit3
Bit3
Bit3
Bit3
58, shows an SPI transfer with the four
Bit 2
Bit 2
Bit 2
Bit 2
Bit 1
Bit 1
Bit 1
Bit 1
LSBit
LSBit
LSBit
LSBit