RM0090: Reference manual - STMicroelectronics

RM0090 Serial peripheral interface (SPI)
● In reception mode:
if data 0x8EAA33 is received:
Figure 291. Receiving 0x8EAA33
Figure 292. I 2 S Philips standard (16-bit extended to 32-bit packet frame with
CPOL = 0)
CK
WS
SD
When 16-bit data frame extended to 32-bit channel frame is selected during the I 2 S
configuration phase, only one access to SPI_DR is required. The 16 remaining bits are
forced by hardware to 0x0000 to extend the data to 32-bit format.
If the data to transmit or the received data are 0x76A3 (0x76A30000 extended to 32-bit), the
operation shown in Figure 293 is required.
Figure 293. Example
First read from Data register
Second read from Data register
0x8EAA 0x3300
Only the 8MSB are right
The 8 LSB will always be 00
Transmission Reception
16-bit data
MSB LSB
Channel left 32-bit
16-bit remaining
0 forced
Only one access to SPI_DR
0X76A3
Channel right
For transmission, each time an MSB is written to SPI_DR, the TXE flag is set and its
interrupt, if allowed, is generated to load SPI_DR with the new value to send. This takes
place even if 0x0000 have not yet been sent because it is done by hardware.
For reception, the RXNE flag is set and its interrupt, if allowed, is generated when the first
16 MSB half-word is received.
In this way, more time is provided between two write or read operations, which prevents
underrun or overrun conditions (depending on the direction of the data transfer).
Doc ID 018909 Rev 3 820/1416