STMicroelectronics STM32F405, Reference Manual

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RM0090 Serial peripheral interface (SPI)
918
In Slave mode ( Figure 249: TI mode - Slave mode, single transfer and Figure 250: TI mode
- Slave mode, continuous transfer ), the SPI baud rate prescaler is used to control the
moment when the MISO pin state changes to HI-Z. Any baud rate can be used thus allowing
to determine this moment with optimal flexibility. However, the baud rate is generally set to
the external master clock baud rate. The time for the MISO signal to become HI-Z (t
release
)
depends on internal resynchronizations and on the baud rate value set in through BR[2:0] of
SPI_CR1 register. It is given by the formula:
Note: This feature is not available for Motorola SPI communications (FRF bit set to 0).
To detect TI frame errors in Slave transmitter only mode by using the Error interrupt (ERRIE
= 1), the SPI must be configured in 2-line unidirectional mode by setting BIDIMODE and
BIDIOE to 1 in the SPI_CR1 register. When BIDIMODE is set to 0, OVR is set to 1 because
the data register is never read and error interrupt are always generated, while when
BIDIMODE is set to 1, data are not received and OVR is never set.
Figure 249. TI mode - Slave mode, single transfer
Figure 250. TI mode - Slave mode, continuous transfer
t
baud_rate
2
----------------------
4 t
pclk
×
+
t
release
t
baud_rate
2
----------------------
6 t
pclk
×
+
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INPUT
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