NuMicro® NUC029LEE/NUC029SEE32-bit Arm® Cortex® -M0 MicrocontrollerAug, 2018 Page 422 of 497 Rev 1.00NUMICRO® NUC029LEE/NUC029SEE TECHNICAL REFERENCE MANUAL6.15.5.5 Byte Suspend FunctionIn Master mode, if REORDER (SPI_CNTRL[19]) is set to 1, a suspend interval of 0.5 ~ 15.5 SPIclock periods will be inserted by hardware between two successive bytes in a transaction word.Both settings of byte suspend interval and word suspend interval are configured in SP_CYCLE(SPI_CNTRL[15:12]).SPIn_CLKSPIn_MOSI0SPIn_MISO0 TX0[30] TX0[24] TX0[23] TX0[22] TX0[16]RX0[30] RX0[24] RX0[22] RX0[16]MSBRX0[31]CLKP=0CLKP=1SuspendInterval1st Transaction Byte 2nd Transaction ByteRX0[23]MSBTX0[31]Figure 6.15-7 Timing Waveform for Byte Suspend6.15.5.6 Slave 3-wire ModeWhen NOSLVSEL (SPI_CNTRL2[8]) is set by software to enable the Slave 3-wire mode, the SPIcontroller can work with no slave select signal in Slave mode. The NOSLVSEL bit only takeseffect in Slave mode. Only three pins, SPIn_CLK, SPIn_MISO0, and SPIn_MOSI0, are requiredto communicate with a SPI master. The SPIn_SS pin can be configured as a GPIO. When theNOSLVSEL bit is set to 1, the SPI slave will be ready to transmit/receive data after the GO_BUSYbit is set to 1. As the number of received bits meets the requirement which defined inTX_BIT_LEN (SPI_CNTRL[7:3]), the unit-transfer interrupt flag, IF (SPI_CNTRL[16]), will be set to1.Note: In Slave 3-wire mode, the SS_LTRIG (SPI_SSR[4]) should be set as 1.6.15.5.7 Dual I/O ModeThe SPI controller also supports Dual I/O transfer when setting the DUAL_IO_EN(SPI_CNTRL2[13]) to 1. Many general SPI flashes support Dual I/O transfer. The DUAL_IO_DIR(SPI_CNTRL2[12]) is used to define the direction of the transfer data. When the DUAL_IO_DIRbit is set to 1, the controller will send the data to external device. When the DUAL_IO_DIR bit isset to 0, the controller will read the data from the external device. This function supports 8, 16, 24,and 32-bit data transfer.The Dual I/O mode is not supported when the Slave 3-wire mode or the Byte Reorder function isenabled.If both the DUAL_IO_EN and DUAL_IO_DIR bits are set as 1, the SPIn_MOSI0 is the even bitdata output and the SPIn_MISO0 will be set as the odd bit data output. If the DUAL_IO_EN is setas 1 and DUAL_IO_DIR is set as 0, both the SPIn_MISO0 and SPIn_MOSI0 will be set as datainput ports.
