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ST72325AR7-Auto Datasheet(PDF) 133 Page - STMicroelectronics |
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ST72325AR7-Auto Datasheet(HTML) 133 Page - STMicroelectronics |
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133 / 243 page  Obsolete Product(s) - Obsolete Product(s) ST72325xxx-Auto Serial peripheral interface (SPI) Doc ID 13770 Rev 3 133/243 Figure 62. Clearing the WCOL bit (Write Collision Flag) software sequence 14.5.4 Single master systems A typical single master system may be configured, using an MCU as the master and four MCUs as slaves (see Figure 63). 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. 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 connected and the slave has not written to its SPIDR register. Other transmission security methods can use ports for handshake lines or data bytes with command fields. Figure 63. Single master / multiple slave configuration Clearing sequence after SPIF = 1 (end of a data byte transfer) 1st Step Read SPICSR Read SPIDR 2nd Step SPIF = 0 WCOL = 0 Clearing sequence before SPIF = 1 (during a data byte transfer) 1st Step 2nd Step WCOL = 0 Read SPICSR Read SPIDR Note: Writing to the SPIDR register instead of reading it does not reset the WCOL bit. RESULT RESULT MISO MOSI MOSI MOSI MOSI MOSI MISO MISO MISO MISO SS SS SS SS SS SCK SCK SCK SCK SCK 5V Slave MCU Slave MCU Slave MCU Slave MCU Master MCU |
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