參數資料
型號: ST72124J2B7
廠商: 意法半導體
英文描述: 8-BIT MCU WITH SINGLE VOLTAGE FLASH MEMORY, ADC, 16-BIT TIMERS, SPI, SCI INTERFACES
中文描述: 8位單電壓閃存,ADC和16位定時器,SPI和脊髓損傷界面微控制器
文件頁數: 74/125頁
文件大?。?/td> 776K
代理商: ST72124J2B7
ST72334J/N, ST72314J/N, ST72124J
74/125
SERIAL PERIPHERAL INTERFACE
(Cont’d)
6.5.4.3 Data Transfer Format
During an SPI transfer, data is simultaneously
transmitted (shifted out serially) and received
(shifted in serially). The serial clock is used to syn-
chronize the data transfer during a sequence of
eight clock pulses.
The SS pin allows individual selection of a slave
device; theother slave devices that are notselect-
ed do not interfere with the SPI transfer.
Clock Phase and Clock Polarity
Four possible timing relationships may be chosen
by software, using the CPOL and CPHA bits.
The CPOL (clock polarity) bit controls the steady
state value of the clock when no data is being
transferred. This bit affects both master and slave
modes.
The combination between the CPOL and CPHA
(clock phase) bits selects the data capture clock
edge.
Figure 49, shows an SPI transfer with the four
combinations of the CPHA and CPOLbits. 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 theslave device.
The SS pin is the slavedevice select input and can
be driven by the master device.
The master device applies data to its MOSI pin-
clock edge before the capture clock edge.
CPHA bit is set
The second edge on the SCK pin (falling edge if
the CPOLbit is reset, rising edgeif the CPOL bit is
set) is the MSBit capture strobe. Data is latched on
the occurrence of the first clock transition.
No write collision should occur even if the SS pin
stays low during a transfer of several bytes (see
Figure 48).
CPHA bit is reset
The firstedge on theSCK pin (falling edge if CPOL
bit is set, rising edge if CPOL bit is reset) is the
MSBit capture strobe. Data is latched on the oc-
currence of the second clock transition.
This pin must be toggled high and low between
each byte transmitted (see Figure 48).
To protect the transmission from a write collision a
low value on the SS pin of a slave device freezes
the data in its DR register and does not allow it to
be altered. Therefore the SS pin must be high to
write a new data byte in the DR without producing
a write collision.
Figure 48. CPHA / SS Timing Diagram
MOSI/MISO
Master
SS
Slave
SS
(CPHA=0)
Slave
SS
(CPHA=1)
Byte 1
Byte 2
Byte 3
VR02131A
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