ST72F264G ST Microelectronics, ST72F264G Datasheet - Page 80

• Manufacturer Part Number: ST72F264G
• Description: (ST72F260G - ST72F264G) 8-BIT MCU
• Manufacturer: ST Microelectronics

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ST72260G, ST72262G, ST72264G
SERIAL PERIPHERAL INTERFACE (Cont’d)
11.4.5.4
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
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.
Note: To prevent a bus conflict on the MISO line
the master allows only one active slave device
during a transmission.
Figure 53. Single Master / Multiple Slave Configuration
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device
Single
Figure
MOSI
SS
as the master and four
SCK
SCK
MOSI
Master
Device
Device
Slave
53).
Master
MISO
MISO
SS
and
Multimaster
MOSI
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SCK
device
Device
Slave
MISO
s as
SS
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.
Multi-Master System
A multi-master system may also be configured by
the user. Transfer of master control could be im-
plemented 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 SPICR register and the MODF
bit in the SPICSR register.
MOSI
SCK
Device
Slave
MISO
SS
MOSI
SCK
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Device
Slave
MISO
SS
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