Using SPI
Last updated
Last updated
The Binho Nova Multi-Protocol USB Host Adapter can serve as a SPI bus controller device which can be configured to meet the needs of nearly any SPI bus implementation. The SPI Clock can be set to a frequency between 500kHz and 12MHz, and all 4 SPI modes are supported. Transfers can be in 8-bit or 16-bit packets. The pin assignments for the SPI protocol are show in the graphic below, indicated in yellow:
The following table gives a brief overview of the available SPI commands.
Commands
Description
Link
CLK
Gets/sets the SPI clock frequency.
ORDER
Gets/sets the SPI bus bit order MSB-first/LSB-first.
MODE
Gets/sets the SPI mode. Modes 0, 1, 2, or 3 are determined by CPOL and CPHA
CPOL
Gets/sets the SPI Clock Polarity. This is related to the SPI mode.
CPHA
Gets/sets the SPI Clock Phase. This is related to the SPI mode.
TXBITS
Gets/sets the number of bits per transmission.
BEGIN
Starts the SPI Controller.
TXRX
Sends/Receives data on the SPI bus.
END
Stops the SPI Controller.
WHR
Transfer 0 to 1024 bytes in a single SPI transaction
Feel free to jump ahead to the ASCII Command Set reference to learn the specifics of each command, or continue below to see an example of how to use these commands to achieve communication on the SPI bus.
The first step in using the Binho Nova Multi-Protocol USB Host adapter as a SPI Controller is to put the adapter into SPI mode using the Device Operating Mode command.
Now the host adapter is in SPI communication mode. The next step is to configure the SPI bus. Here are the default settings:
SPI Clock Frequency = 2MHz
SPI Mode = 0 (CPOL = 0, CPHA = 0)
8 Bit Packet Size (TXBITS)
MSB-First bit ordering.
Let's change the bus configuration to a 5MHz clock:
And let's setup the IO0 pin to use as our chip-select signal. For this device, the chip-select signal is active low, so IO0 should be a digital output that is idle high.
The bus is now all setup and ready to go.
Begin by putting the SPI signals (SCK, SDI, SDO) in their initial state simply by using the BEGIN command.
In order to begin transferring data over the SPI bus, one must first assert the chip-enable/chip-select signal of the peripheral device.
Now the chip-select signal is asserted and our target SPI peripheral device is ready to communicate.
Let's do a 5 byte transfer, which consists of sending a 1-byte command and then clocking out a 4-byte response.
Well that sure was tedious... and something seems strange. Looks like the peripheral device didn't return any data because we were too slow. It's fairly common for devices to have timing requirements regarding the duration of a transfer. Thankfully, for situations like this, we can use the buffer! Let's load up the buffer with our data:
Now let's perform the SPI transaction using BUF0 and send 5 bytes from BUF0, using IO0 as the ChipSelect pin (active-low):
Since we are using the buffer, the received data is also placed into the buffer. Let's read it out and see if the device responded as expected:
Awesome! The expected response was received. That's pretty much all it takes to use the Binho Nova Multi-Protocol USB Host Adapter to speak with SPI devices. Simply clear out the buffer and repeat the process to start another transfer.
Note that this example didn't cover using IO1, but it's not hard to imagine how this could be used as an interrupt pin, or to control the chip-select pin of a second peripheral device on the SPI bus.
Feel free to take a look in the examples section to see how to use the python library to use this in an automated way:
For use cases where a lot of data is being read/written and speed is important, the WHR command should be utilized to minimize the amount of communication between the Nova and the host PC. You can learn all the details about this here.
Otherwise, stick around here and move to the next page to see a similar tutorial on an I2C bus.
