8-Bit Word Lengths - Analog Devices ADSP-21261 SHARC Hardware Reference Manual

SPI Word Lengths

8-Bit Word Lengths

Eight-bit word lengths can be used when transmitting or receiving. When
transmitting, the SPI port sends out only the lower eight bits of the word
written to the SPI buffer.
For example, if the processor executes the instructions below, the SPI port
transmits
0x78
r0 = 0x12345678
dm(TXSPI) = r0;
When receiving, the SPI port packs the 8-bit word to the lower 32 bits of
the buffer while the upper bits in the registers are zeros.
RXSPI
For example, if an SPI host sends the processor the 32-bit word
, the processor receives the following words:
0x12345678
0x00000078 //first word
0x00000056 //second word
0x00000034 //third word
0x00000012 //forth word
This code works only if the
receiver, and the
and receiver, and
the order
0x12
16-Bit Word Lengths
Sixteen-bit word lengths can be used when transmitting or receiving.
When transmitting, the SPI port sends out only the lower 16 bits of the
word written to the SPI buffer.
10-30
.
MSBF
frequency is small. If
SPICLK
has a small frequency, the received words follow
SPICLK
, , , .
0x34 0x56 0x78
ADSP-2126x SHARC Processor Hardware Reference
bit is zero in both the transmitter and
MSBF
= 1 in the transmitter