SPI bus

The Serial Peripheral Interface bus (SPI) is a synchronous serial communication interface specification used for short distance communication, primarily in embedded systems. The interface was developed by Motorola and has become a de facto standard. Typical applications include sensors, Secure Digital cards, and liquid crystal displays.

SPI devices communicate in full duplex mode using a master-slave architecture with a single master. The master device originates the frame for reading and writing. Multiple slave devices are supported through selection with individual slave select (SS) lines.

ECSPI

The Enhanced Configurable Serial Peripheral Interface (ECSPI) is a full-duplex, synchronous, four-wire serial communication block. The ECSPI contains a 64 x 32 receive buffer (RXFIFO) and a 64 x 32 transmit buffer (TXFIFO). With data FIFOs, the ECSPI allows rapid data communication with fewer software interrupts. The figure below shows a block diagram of the ECSPI.

Key features of the ECSPI include:

• Full-duplex synchronous serial interface
• Master/Slave configurable
• Four Chip Select (SS) signals to support multiple peripherals
• Transfer continuation function allows unlimited length data transfers
• 32-bit wide by 64-entry FIFO for both transmit and receive data
• Polarity and phase of the Chip Select (SS) and SPI Clock (SCLK) are configurable
• Direct Memory Access (DMA) support
• Max operation frequency up to the reference clock frequency.

The ECSPI supports the modes described in the indicated sections:

• Master Mode
• Slave Mode
• Low Power Modes

UDOO Neo SPI channels

UDOO Neo exposes 3 ECSPI channels:

	MISO	MOSI	CLOCK	SS0	SS1	SS2	SS3	Default core at boot
ECSPI_2	20	21	38	39	-	-	-	A9 (gpio mode)
ECSPI_3	18 / A1 *	A0 *	A4 *	19 / A5 *	21	20	-	A9 (gpio mode)
ECSPI_5	12 / 40	11 / 43	13 / 42	10 / 41	-	-	-	M4

* Analogs pin can also be connected to A9 core using phisical signal mux 74VHC4053AFT (U12, U13).

For more detailed information look at the Chapter 22 of the iMX 6SoloX Reference Manual.

ECSPI 2

ECSPI 2 has only for signals (MISO, MOSI, SCLK and SS0); By default the ECSPI 2 signals are assigned to A9 in GPIO mode. In order to enable ECSPI, follow this guide.

ECSPI 3

ECSPI 3 is a full SPI, including Select Signals (SS0, SS1, SS2).

ECSPI 5

ECSPI 5 has the same pin order, function, and position as Arduino UNO. By default it is assigned to the Arduino 101-compatible M4 core.