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--- spi_group [ 17.08.2025 05:40] – created lars
+++ spi_group [ 17.08.2025 05:52] (current) – lars
@@ Line 1: / Line 1: @@
+====== SPI ======
+Different variants exist. Usually SPI refers to the Motorola Serial Peripheral Interface. Other variants are the Texas Instruments Serial protocol (SSP) and the National Instruments Microwire.
+===== Protocol =====
+Most significant bit first
+===== Modes =====
+There are 4 Modes. Defied by the two settings "clock polarity" CPOL and "clock phase" CPHA.
+"clock polarity" CPOL = 0:
+  - Clock line is low when idle.
+"clock polarity" CPOL = 1:
+  - Clock line is high when idle.
+"clock phase" CPHA = 0:
+  - first data bit is output on /CS activating (going low).
+  - data bits change when clock goes to idle level.
+  - data bits are read when clock comes from idle level.
+"clock phase" CPHA = 1:
+  - first data bit starts on first edge after /CS activates.
+  - data bits change when clock comes from idle level.
+  - data bits are read when clock goes to idle level.
+^ mode ^ CPOL ^ CPHA ^ write bit                               ^ read bit        ^
+| 0    | 0    | 0    | clock goes low, and when /CS activates  | clock goes high |
+| 1    | 0    | 1    | clock goes high                         | clock goes low  |
+| 2    | 1    | 0    | clock goes high, and when /CS activates | clock goes low  |
+| 3    | 1    | 1    | clock goes low                          | clock goes high |
 ===== SPI group =====
@@ Line 129: / Line 165: @@
 **type**: int (Hz)
+===== API =====
+The part "signal_name" in the described functions will be replaced by the name of the signal. E.g. if your signal is called "audio" then the API function "signal_name_transfer" will become "audio_transfer".
+<code>
+void signal_name_transfer(const uint8_t *data_send,
+                          const uint8_t *data_receive,
+                          const uint32_t length )</code>
+Will send "length" bytes from the buffer "data_send" out on MOSI and will receive the same amount of bytes from MISO into the buffer "data_receive".