how spi decide when to receive (miso) and when to transmit (mosi)

[beginner_EDA]

how spi decide when to receive(miso) and when to transmit(mosi)

Hi,
I already found some info here:
https://learn.sparkfun.com/tutorials/serial-peripheral-interface-spi

but I would like to know specificially:

how spi decide when to receive(miso)?

 

[rberek]

Re: how spi decide when to receive(miso) and when to transmit(mosi)

The datasheet for the slave device will tell you exactly what to send to the slave and how/when the slave will respond to the transfer.

r.b.

 

[KlausST]

Re: how spi decide when to receive(miso) and when to transmit(mosi)

Hi,

SPI master sends a byte, at the same time the slave sends a byte.
Clk is generated by the master.

Klaus

 

[ads-ee]

Re: how spi decide when to receive(miso) and when to transmit(mosi)

Hi,

SPI master sends a byte, at the same time the slave sends a byte.
Clk is generated by the master.

Klaus

To add to this...the typical read protocol on SPI would be:
1. the master sends one or more bytes as address, the slave returns byte(s) (which could contain anything).
2. the master pauses, letting the slave get data for that address
3. the master sends data bytes (dummy data), and receives the slave read data while sending the dummy bytes.

 

[FvM]

Re: how spi decide when to receive(miso) and when to transmit(mosi)

SPI master sends a byte, at the same time the slave sends a byte.

Yes, the communication is potentially full duplex. But the option isn't used respectively not useable in all applications.

 

[asdf44]

Re: how spi decide when to receive(miso) and when to transmit(mosi)

And one thing not said: Chip Select (CS or SS).

Every (nearly) SPI device will have a chip select which determines when it listens to MOSI and when it transmits on MISO.

Typically the device will go high impedance on MISO when chip select isn't active which lets you have multiple devices on one set of CLK/MISO/MOSI lines.