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ST72321J Datasheet(PDF) 91 Page - STMicroelectronics |
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ST72321J Datasheet(HTML) 91 Page - STMicroelectronics |
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91 / 179 page  ST72321J 91/179 SERIAL PERIPHERAL INTERFACE (Cont’d) 10.5.5 Error Flags 10.5.5.1 Master Mode Fault (MODF) Master mode fault occurs when the master device has its SS pin pulled low. When a Master mode fault occurs: – The MODF bit is set and an SPI interrupt re- quest is generated if the SPIE bit is set. – The SPE bit is reset. This blocks all output from the device and disables the SPI periph- eral. – The MSTR bit is reset, thus forcing the device into slave mode. Clearing the MODF bit is done through a software sequence: 1. A read access to the SPICSR register while the MODF bit is set. 2. A write to the SPICR register. Notes: To avoid any conflicts in an application with multiple slaves, the SS pin must be pulled high during the MODF bit clearing sequence. The SPE and MSTR bits may be restored to their orig- inal state during or after this clearing sequence. Hardware does not allow the user to set the SPE and MSTR bits while the MODF bit is set except in the MODF bit clearing sequence. 10.5.5.2 Overrun Condition (OVR) An overrun condition occurs, when the master de- vice has sent a data byte and the slave device has not cleared the SPIF bit issued from the previously transmitted byte. When an Overrun occurs: – The OVR bit is set and an interrupt request is generated if the SPIE bit is set. In this case, the receiver buffer contains the byte sent after the SPIF bit was last cleared. A read to the SPIDR register returns this byte. All other bytes are lost. The OVR bit is cleared by reading the SPICSR register. 10.5.5.3 Write Collision Error (WCOL) A write collision occurs when the software tries to write to the SPIDR register while a data transfer is taking place with an external device. When this happens, the transfer continues uninterrupted; and the software write will be unsuccessful. Write collisions can occur both in master and slave mode. See also Section 10.5.3.2 Slave Select Management. Note: a "read collision" will never occur since the received data byte is placed in a buffer in which access is always synchronous with the MCU oper- ation. The WCOL bit in the SPICSR register is set if a write collision occurs. No SPI interrupt is generated when the WCOL bit is set (the WCOL bit is a status flag only). Clearing the WCOL bit is done through a software sequence (see Figure 56). Figure 56. Clearing the WCOL bit (Write Collision Flag) Software Sequence 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 regis- ter instead of reading it does not reset the WCOL bit RESULT RESULT |
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