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Why is miso high on a SPI master?
The reason for having high impedance on MISO (Master In Slave Out) in the slave is so you can have several slaves on the same SPI bus. When SS (Slave Select) is high the slave makes its MISO output high impedance, so it won’t collide with another slave which might be selected.
What happens when a MISO signal is high?
However, because my SPI master sees a logic high signal on MISO while !CS is low and clock pulses are being sent out, it sees this as a valid transaction and stores the byte. This means that every time I send an address/command and read data back, I receive two bytes of data- 0xFF (or 0x00 if data is already ready), and then my actual data.
Why does my SPI master go high when I select a device?
When I select the device via !CS, the !RDY/DOUT line goes high to indicate that data is not ready to be sent from the device. However, because my SPI master sees a logic high signal on MISO while !CS is low and clock pulses are being sent out, it sees this as a valid transaction and stores the byte.
Why is the MOSI line at the master always high?
1 Answer 1. MOSI (Master Out Slave In) is an input on the slave, so it is always high impedance. The slave won’t be able to tell if the MOSI line is high impedance at the master, but then it doesn’t need to.
Why is Mosi always high on a microcontroller?
MOSI (Master Out Slave In) is an input on the slave, so it is always high impedance. The slave won’t be able to tell if the MOSI line is high impedance at the master, but then it doesn’t need to. If the slave is selected (SS low) then it expects to see 1’s and 0’s on MOSI. If it is deselected then it doesn’t care.
What happens if the MOSI pin is high or low?
Even if the MOSI pin is also driving the line, either a HIGH or a LOW level, it will only result in a resistor load and won’t change the level driven by the sensor. The resistor value be must chosen so that the current it draws is bellow both the uC and sensor limits.