![]() If a waiting period is required, such as for an analog-to-digital conversion, the master must wait for at least that period of time before issuing clock cycles.ĭuring each SPI clock cycle, a full-duplex data transmission occurs. The master then selects the slave device with a logic level 0 on the select line. To begin communication, the bus master configures the clock, using a frequency supported by the slave device, typically up to a few MHz. (Note: refer to the ‘ Variations’ section later in this article for further details.)Ī typical hardware setup using two shift registers to form an inter-chip circular buffer Devices without tri-state outputs cannot share SPI bus segments with other devices without using an external tri-state buffer. Most slave devices have tri-state outputs so their MISO signal becomes high impedance ( electrically disconnected) when the device is not selected. With multiple slave devices, an independent SS signal is required from the master for each slave device. An example is the Maxim MAX1242 ADC, which starts conversion on a high→low transition. Some slaves require a falling edge of the chip select signal to initiate an action. If a single slave device is used, the SS pin may be fixed to logic low if the slave permits it. The SPI bus can operate with a single master device and with one or more slave devices. SS, SS, SSEL, NSS, /SS, SS# (slave select).SDI, DI, DIN, SI - on master devices connects to MISO on slave, or to above connections.SDO, DO, DOUT, SO - on slave devices connects to MISO on master, or to below connections.SOMI, MRST - correspond to MISO on both master and slave devices, connects to each other. ![]()
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