參數(shù)資料
型號: M68HC11D3CFB1
廠商: FREESCALE SEMICONDUCTOR INC
元件分類: 微控制器/微處理器
英文描述: 8-BIT, MROM, 1 MHz, MICROCONTROLLER, PQFP44
封裝: QFP-44
文件頁數(shù): 105/124頁
文件大?。?/td> 5398K
代理商: M68HC11D3CFB1
SERIAL PERIPHERAL INTERFACE
TECHNICAL DATA
8-3
Figure 8-2 SPI Transfer Format
8.2.1 Clock Phase and Polarity Controls
Software can select one of four combinations of serial clock phase and polarity using
two bits in the SPI control register (SPCR). The clock polarity is specified by the CPOL
control bit, which selects an active high or active low clock, and has no significant ef-
fect on the transfer format. The clock phase (CPHA) control bit selects one of two dif-
ferent transfer formats. The clock phase and polarity should be identical for the master
SPI device and the communicating slave device. In some cases, the phase and polar-
ity are changed between transfers to allow a master device to communicate with pe-
ripheral slaves having different requirements.
When CPHA equals zero, the slave select (SS) line must be negated and reasserted
between each successive serial byte. Also, if the slave writes data to the SPI data reg-
ister (SPDR) while SS is active low, a write collision error results.
When CPHA equals one, the SS line can remain low between successive transfers.
8.3 SPI Signals
The following paragraphs contain descriptions of the four SPI signals: master in slave
out (MISO), master out slave in (MOSI), serial clock (SCK), and SS.
SPI TRANSFER FORMAT 1
2345678
1
SCK (CPOL = 1)
SCK (CPOL = 0)
SCK CYCLE #
SS (TO SLAVE)
654321
LSB
MSB
654321
LSB
1
2
3
5
4
SLAVE CPHA=1 TRANSFER IN PROGRESS
MASTER TRANSFER IN PROGRESS
SLAVE CPHA=0 TRANSFER IN PROGRESS
1. SS ASSERTED
2. MASTER WRITES TO SPDR
3. FIRST SCK EDGE
4. SPIF SET
5. SS NEGATED
SAMPLE INPUT
DATA OUT
(CPHA = 0)
SAMPLE INPUT
DATA OUT
(CPHA = 1)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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