Control B

  0x01 8 - 0x00  

Control B

Bit  7 6 5 4 3 2 1 0  
  BUFEN BUFWR       SSD MODE[1:0]  
Access  R/W R/W       R/W R/W R/W  
Reset  0 0       0 0 0  

Bit 7 – BUFEN: Buffer Mode Enable

Buffer Mode Enable

Writing this bit to ‘1’ enables Buffer mode. This will enable two receive buffers and one transmit buffer. Both will have separate interrupt flags, transmit complete and receive complete.

Bit 6 – BUFWR: Buffer Mode Wait for Receive

Buffer Mode Wait for Receive

When writing this bit to ‘0’, the first data transferred will be a dummy sample.

0 One SPI transfer must be completed before the data are copied into the shift register
1 If writing to the Data register when the SPI is enabled and SS is high, the first write will go directly to the shift register

Bit 2 – SSD: Client Select Disable

Client Select Disable

If this bit is set when operating as SPI Host (MASTER = 1 in SPIn.CTRLA), SS does not disable Host mode.

0 Enable the Client Select line when operating as SPI host
1 Disable the Client Select line when operating as SPI host

Bits 1:0 – MODE[1:0]: Mode


These bits select the Transfer mode. The four combinations of SCK phase and polarity concerning the serial data are shown below. These bits decide whether the first edge of a clock cycle (leading edge) is rising or falling and whether data setup and sample occur on the leading or trailing edge. When the leading edge is rising, the SCK signal is low when idle, and when the leading edge is falling, the SCK signal is high when idle.

0x0 0

Leading edge: Rising, sample
Trailing edge: Falling, setup

0x1 1

Leading edge: Rising, setup
Trailing edge: Falling, sample

0x2 2

Leading edge: Falling, sample
Trailing edge: Rising, setup

0x3 3

Leading edge: Falling, setup
Trailing edge: Rising, sample