ST72621L4M1(2002) View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST72621L4M1
(Rev.:2002)

LOW SPEED USB 8-BIT MCU WITH 3 ENDPOINTS, FLASH OR ROM MEMORY, LVD, WDG, 10-BIT ADC, 2 TIMERS, SCI, SPI

STMicroelectronics 

ST7262

SERIAL PERIPHERAL INTERFACE (Cont’d)

10.4.5.4 Single Master System

A typical single master system may be configured,

using an MCU as the master and four MCUs as

slaves (see Figure 45).

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.

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 45. 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

61/133

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