ST STM32F40 Series User Manual

RM0090 Serial peripheral interface (SPI)
Doc ID 018909 Rev 4 802/1422
In Slave mode (Figure 274: TI mode - Slave mode, single transfer and Figure 275: TI mode -
Slave mode, continuous transfer), the SPI baud rate prescaler is used to control the moment
when the MISO pin state changes to HiZ. 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 HiZ (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 274. TI mode - Slave mode, single transfer
Figure 275. TI mode - Slave mode, continuous transfer
t
baud_rate
2
---------------------- 4t
pclk
×+ t
release
t
baud_rate
2
---------------------- 6t
pclk
×+<<
ai18434
MSBIN
MOSI
input
NSS
input
SCK
input
trigger
edge
sampling
edge
trigger
edge
sampling
edge
trigger
edge
sampling
edge
DONTCARE LSBIN
DONTCARE
MISO
output
1 or 0 MSBOUT
LSBOUT
t
Release
ai18435
MSBIN
MOSI
input
NSS
input
SCK
input
trigger sampling trigger sampling trigger sampling
DONTCARE LSBIN
DONTCARE
MISO
output
1 or 0 MSBOUT
LSBOUT
MSBIN LSBIN
MSBOUT LSBOUT
FRAME 1 FRAME 2

ST STM32F40 Series Specifications

General

Brand	ST
Model	STM32F40 Series
Category	Microcontrollers
Language	English