Error Flags - ST STM32F100 Series Reference Manual

RM0041
DMA capability with CRC
When SPI communication is enabled with CRC communication and DMA mode, the
transmission and reception of the CRC at the end of communication are automatic that is
without using the bit CRCNEXT. After the CRC reception, the CRC must be read in the
SPI_DR register to clear the RXNE flag.
At the end of data and CRC transfers, the CRCERR flag in SPI_SR is set if corruption
occurs during the transfer.
21.3.10

Error flags

Master mode fault (MODF)
Master mode fault occurs when the master device has its NSS pin pulled low (in NSS
hardware mode) or SSI bit low (in NSS software mode), this automatically sets the MODF
bit. Master mode fault affects the SPI peripheral in the following ways:
• The MODF bit is set and an SPI interrupt is generated if the ERRIE bit is set.
•
The SPE bit is cleared. This blocks all output from the device and disables the SPI
interface.
•
The MSTR bit is cleared, thus forcing the device into slave mode.
Use the following software sequence to clear the MODF bit:
1. Make a read or write access to the SPI_SR register while the MODF bit is set.
2. Then write to the SPI_CR1 register.
To avoid any multiple slave conflicts in a system comprising several MCUs, the NSS pin
must be pulled high during the MODF bit clearing sequence. The SPE and MSTR bits can
be restored to their original state after this clearing sequence.
As a security, hardware does not allow the setting of the SPE and MSTR bits while the
MODF bit is set.
In a slave device the MODF bit cannot be set. However, in a multimaster configuration, the
device can be in slave mode with this MODF bit set. In this case, the MODF bit indicates
that there might have been a multimaster conflict for system control. An interrupt routine can
be used to recover cleanly from this state by performing a reset or returning to a default
state.
Overrun condition
An overrun condition occurs when the master device has sent data bytes and the slave
device has not cleared the RXNE bit resulting from the previous data byte transmitted.
When an overrun condition occurs:
•
the OVR bit is set and an interrupt is generated if the ERRIE bit is set.
In this case, the receiver buffer contents are not updated with the newly received data from
the master device. A read from the SPI_DR register returns this byte. All other subsequently
transmitted bytes are lost.
Clearing the OVR bit is done by a read from the SPI_DR register followed by a read access
to the SPI_SR register.
RM0041 Rev 6
Serial peripheral interface (SPI)
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