The electrical lines
The SPI bus lines are reported in the following table:
|
Name |
Description |
|---|---|
|
SCLK: Serial clock |
This is the bus clock signal |
|
MOSI: Master Out Slave In |
This is the bus data signal (Master Output Slave Input) |
|
MISO: Master In Slave Out |
This is the bus data signal (Master Input Slave Output) |
|
SS: Slave Select |
This is the chip or slave select signal (one per slave) |
|
GND |
This is the common ground |
Tip
It's quite common that an SPI controller has a few SS lines (usually 2 or 3), so when more SPI devices are needed at once, a trick must be used. The solution is to generate the needed SS signals using the common GPIO lines managed by the driver, instead of by the controller hardware itself.
Despite the fact that this behavior can permit a very large number of devices to be connected to a single master, it slows down the whole bus performances, as the signals are driven in the software rather than in the hardware. Also, note that this feature must be supported by the SPI master...