ST52F510FMB6 STMICROELECTRONICS [STMicroelectronics], ST52F510FMB6 Datasheet - Page 101

• Manufacturer Part Number: ST52F510FMB6
• Description: 8-BIT INTELLIGENT CONTROLLER UNIT ICU Two Timer/PWMs, ADC, I2C, SPI, SCI
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Figure 15.5 Clearing the WCOL bit (Write Collision Flag) Software Sequence
15.4.6 Overrun Condition.
An overrun condition occurs when the master
device has sent several data bytes and the slave
device hasn’t cleared the SPIF bit issued from the
previous data byte transmitted.
In this case, the receiver buffer contains the byte
sent after the SPIF bit was last cleared. A read to
the SPI_IN register returns this byte. All other
bytes are lost.
This condition is not detected by the SPI
peripheral.
15.4.7 Single Master and Multimaster Configu-
rations.
There are two types of SPI systems:
– Single Master System
– Multimaster System
Single Master System
A typical single master system may be configured,
using an ICU as the master and four ICUs as
slaves (see Figure 15.6).
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.
1st Step
2nd Step
Clearing sequence after SPIF = 1 (end of a data byte transfer)
Clearing sequence before SPIF = 1 (during a data byte transfer)
1st Step
2nd Step
Read SPI_STATUS_CR
Read SPI_IN
THEN
SPIF =0
WCOL=0
Read SPI_IN
Read SPI_STATUS_CR
OR
THEN
WCOL=0
Read SPI_STATUS_CR
Write SPI_IN
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: In order 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 data byte received. 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 its
SPI_OUT register.
Other transmission security methods can use ports
for handshake lines or data bytes with command
fields.
Multi-master System
A multi-master 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 multi-master system is principally handled by
the MSTR bit in the SPI_CR register and the
MODF bit in the SPI_STATUS_CR register.
Note: Writing in SPI_OUT regis-
ter instead of reading in SPI_IN
do not reset WCOL bit
THEN
SPIF =0
WCOL=0
WCOL=1
before the 2nd step
ST52F510/F513/F514
if no transfer has started
if a transfer has started
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