Abov MC96FR364B, Руководство пользователя

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November, 2018 Rev.1.4 131
11.9.10 SPI Mode
The USART can be set to operate in industrial standard SPI compliant mode. The SPI mode has the
following features.
- Full duplex, three-wire synchronous data transfer
- Master or Slave operation
- Supports all four SPI modes of operation (mode0, 1, 2, and 3)
- Selectable LSB first or MSB first data transfer
- Double buffered transmit and receive
- Programmable transmit bit rate
When SPI mode is enabled (UMSEL[1:0]=11
B
), the Slave Select (SS) pin becomes active low input in
slave mode operation, or can be output in master mode operation if SPISS bit is set.
Note that during SPI mode of operation, the pin RXD is renamed as MISO and TXD is renamed as
MOSI for compatibility to other SPI devices.
11.9.10.1 SPI Clock Formats and Timing
To accommodate a wide variety of synchronous serial peripherals from different manufacturers, the
USART has a clock polarity bit (UCPOL) and a clock phase control bit (UCPHA) to select one of four
clock formats for data transfers. UCPOL selectively insert an inverter in series with the clock. UCPHA
chooses between two different clock phase relationships between the clock and data. Note that
UCPHA and UCPOL bits in UCTRL1 register have different meaning according to the UMSEL[1:0]
bits which decides the operating mode of USART.
Table below shows four combinations of UCPOL and UCPHA for SPI mode 0, 1, 2, and 3.
SPI Mode UCPOL UCPHA Leading Edge Trailing Edge
0 0 0 Sample (Rising) Setup (Falling)
1 0 1 Setup (Rising) Sample (Falling)
2 1 0 Sample (Falling) Setup (Rising)
3 1 1 Setup (Falling) Sample (Rising)
Table 11-17 SPI Mode by UCPOL & UCPHA