ST72321B STMICROELECTRONICS [STMicroelectronics], ST72321B Datasheet - Page 94

• Manufacturer Part Number: ST72321B
• Description: 64/44-pin 8-bit MCU with 32 to 60K Flash/ROM, ADC, five timers, SPI, SCI, I2C interface
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

SERIAL PERIPHERAL INTERFACE (Cont’d)
10.5.5.4 Single Master Systems
A typical single master system may be configured,
using an MCU as the master and four MCUs as
slaves (see
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 will be forced to be inputs at
that time, thus disabling the slave devices.
Figure 60. Single Master / Multiple Slave Configuration
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5V
Figure
MOSI
SCK
SS
SCK
MOSI
MCU
Master
Slave
MCU
60).
MISO
MISO
SS
MOSI
SCK
MCU
Slave
MISO
SS
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.
MOSI
SCK
MCU
Slave
MISO
SS
MOSI
SCK
MCU
Slave
MISO
SS