36.4 Functional Description

The SQI module, which is an industry standard synchronous serial link, helps communicate with multiple SPI compatible devices such as serial EEPROMs and serial Flash devices.

The SQI module has three interfaces, one external to the device (SQI Bus Interface) that connects to the external Flash memories or other serial devices, and two internal (Bus Client interface for control register reads/writes and Bus Host for data transfers), as illustrated in the Block Diagram.

The SQI bus interface consists of four data lines (SQID3-SQID0), a clock line (SQICLK), and two select lines (SQICS0 and SQICS1). As mentioned earlier, the SQI module supports Single Lane (SPI mode), Dual Lane, and Quad Lane modes of operation.

The SQI module operates in both Single Data Rate (SDR) and Double Data Rate (DDR) modes. In DDR mode, the data transition occurs on both edges of the clock providing double the throughput.

Note: The SQI module is a half-duplex, synchronous serial interface when in Host mode of operation.

The SQI module has configurable transmit and receive buffers, programmable baud rates through the internal clock divider, clock phase, and clock polarity control for efficient data operations. Transmit and receive buffers can be accessed through SQI1TXDATA and SQI1RXDATA registers. Similarly, the control buffer can be accessed through the SQI1CON register and is mainly used to pipeline the operations. The SQI module operates in three transfer modes: DMA, PIO, and XIP. All three modes use the control buffer to pipeline the command/data sequences on the SQI bus.

The SQI module supports two data flow modes: SPI Mode 0 and Mode 3. Each transfer mode (XIP/PIO/DMA) can use any of the data flow modes as desired by the application.

DMA and PIO modes are typically used to transfer the data to and from external serial Flash memory, whereas, eXecute In Place (XIP) mode is used to execute the code out of the external serial Flash memory. DMA mode uses the internal DMA engine and buffer descriptors to transfer data between source and destination memory spaces off-loading the Host processor during which time, accessing SQI1TXDATA, SQI1RXDATA, and SQI1CON functionally will not yield expected results. However, PIO mode engages the Host processor to access the contents of the external serial Flash memory using a bit-band method through the transmit and receive data registers. Refer to SQI Transfer Modes for a detailed description of each transfer mode.

The SQI module supports automatic memory status check reducing software burden. For a block diagram of the SQI module, refer to the Block Diagram.