I2C and SPI communication on FPGA

[caillotantoine]

Overview

I2C and SPI are widely used communication buses. This example is based on the I2C&SPI API available on VIPM to read the data of 4 different sensors through the both buses.

Description

The example has been tested on the PXI-7854R board, but I expect it to work on other similar boards (cf. I2C&SPI API device compatibility). The goal is to read the temperature from two temperature sensors using the SPI Bus and to get the data from a Gyroscope and an accelerometer through the I2C bus. The FPGA hosts the circuitry of the generic layer for the I2C and the SPI and every command are sent from the host VI. 

On the breadboard, everything is wired that way: 

Diagram of the circuit

Power is supplied from an FPGA pin with 3.3V. The pull-up resistor mustn't be forgotten on each line (Value advised: 4.7k).

Note: on the ADXL 345, to activate the I2C: ground the SDO pin.

Hardware and Software Requirements

 Sensors:

• LM 74 (temperature sensor) x2
• ADXL 345 (accelerometer)
• MPU 6050 (gyroscope)

Hardware:

• PXI-7854R (FPGA)
• PXIe-8135 (PXI Controller under Windows 7)
• SCB-68

Software:

• LabVIEW 2018
• FPGA Module
• I2C&SPI API (available on VIPM : I2C&SPI API)
• R Serie Driver (Version 2018)

Steps to Implement or Execute Code

First of all, build the circuit with the different sensors and wire them to the FPGA through the SCB-68. If you are using the same hardware, I advise you to use the following pins:

SCB-68 Pin	FPGA Pin	Breadboard Pin
67	Connector1/DIO37	SDA
33	Connector1/DIO36	SCL
32	Connector1/DIO24	MISO
65	Connector1/DIO33	SCLK
31	Connector1/DIO32	MOSI
63	Connector1/DIO29	CS0
29	Connector1/DIO28	CS1
57	Connector1/DIO22	3.3V
23	GND	GND

Circuit example

Once you are done, open the project.

ProjectYou if you do not use the same device, you will need to reconfigure the FPGA IO: Open the FPGA and the VI main FPGA.vi

Then, modify the IO from the pin you choose on your FPGA.

Configure the SPI pins.

Configure the I2C pins.

Note: You can see that I modified the name of the FPGA's Pins to make the program easier to read. 

Once you reconfigured your pins, recompile the FPGA. Once you are done, you can run the VI final_main.vi. 

final_main.vi

Note: to program the FPGA, you can just drag and drop the I2C Engine.vi on your FPGA code. It will make the whole generic layer for you.

Use the I2C Engine.vi to avoid complicated FPGA programming. You can do so for the SPI.

Additional Information or References

LM74 :

LM74 Datasheet

ADXL 345:

ADXL345 Datasheet

MPU 6050:

Register Map

Datasheet

[Tianci]

HELLO,

I have a question. What does the clock rate mean in SPI WRITE/READ?

Thank you!

[caillotantoine]

Hello Tianci,

The clock rate in the library is the frequency in MHz of the SPI clock line, we often use 1MHz. In my case I bypassed a conversion VI to directly set the clock divider.

Best, 

Antoine

[spalinowy]

I started the program, but noticed that the values refresh very slowly (every 1 s or so). How can I get the highest possible data reading speed?