Figure 75. Clearing The Wcol Bit (Write Collision Flag) Software Sequence - STMicroelectronics ST72361 Auto Series Manual

Serial peripheral interface (SPI)

Figure 75. Clearing the WCOL bit (write collision flag) software sequence

1st Step
2nd Step
Single master and multimaster configurations
There are two types of SPI systems:
●
Single Master System
● Multimaster System
Single master system
A typical single master system may be configured using a device as the master and four
devices as slaves (see
The master device selects the individual slave devices by using four pins of a parallel port to
control the four SS pins of the slave devices.
The SS pins are pulled high during reset since the master device ports will be forced to be
inputs at that time, thus disabling the slave devices.
Note: To prevent a bus conflict on the MISO line, the master allows only one active slave
device during a transmission.
For more security, the slave device may respond to the master with the received data byte.
Then the master will receive the previous byte back from the slave device if all MISO and
MOSI pins are connected and the slave has not written to its SPIDR register.
Other transmission security methods can use ports for handshake lines or data bytes with
command fields.
Multimaster system
A multimaster system may also be configured by the user. Transfer of master control could
be implemented using a handshake method through the I/O ports or by an exchange of
code messages through the serial peripheral interface system.
The multimaster system is principally handled by the MSTR bit in the SPICR register and
the MODF bit in the SPICSR register.
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Clearing sequence after SPIF = 1 (end of a data byte transfer)
Read SPICSR
RESULT
SPIF = 0
Read SPIDR
WCOL = 0
Clearing sequence before SPIF = 1 (during a data byte transfer)
1st Step
2nd Step
Figure 76).
Doc ID 12468 Rev 3
Read SPICSR
RESULT
Read SPIDR
WCOL = 0
ST72361xx-Auto
Note: Writing to the SPIDR register
instead of reading it does not reset
the WCOL bit