The SPI consists of four different signal lines. These lines are the shift clock
(SCK), the Master Out Slave In line (MOSI), the Master In Slave Out line (MISO) and the
active low Slave Select line (
SS). When the SPI is enabled, the
data direction of the MOSI, MISO, SCK, and
SS pins are
overridden according to the following table.
Table 1. SPI Pin Overrides| Pin |
Direction Master Mode |
Direction Slave Mode |
|---|
| MOSI |
User Defined |
Input |
| MISO |
Input |
User Defined |
| SCK |
User Defined |
Input |
| SS |
User Defined |
Input |
This table shows that the input pins are automatically configured. The
output pins must be initialized manually by the software. The reason for this is to
avoid damages through driver contention.