ST7L05 Datasheet, PDF (59/104 Pages) STMicroelectronics – 8-bit MCU for automotive with single voltage Flash memory, data EEPROM, ADC, timers, SPI

ST7L05, ST7L09
SERIAL PERIPHERAL INTERFACE (Cont’d)
11.3.5.4 Single Master Systems
A typical single master system may be configured,
using an MCU as the master and four MCUs as
slaves (see Figure 37).
The master device selects the individual slave de-
vices 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 are forced as 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 con-
nected and the slave has not written to its SPIDR
register.
Other transmission security methods can use
ports for handshake lines or data bytes with com-
mand fields.
Figure 37. Single Master / Multiple Slave Configuration
SS
SCK
Slave
MCU
MOSI MISO
SS
SCK
Slave
MCU
MOSI MISO
SS
SCK
Slave
MCU
MOSI MISO
SS
SCK
Slave
MCU
MOSI MISO
MOSI MISO
SCK
Master
MCU
5V
SS
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