Motivation

Two of the most popularly used protocols in embedded design systems are the SPI and I²C communication protocols. However, a lot of embedded systems only support a singular communication protocol, which creates a problem when an embedded system with a different communication protocol wishes to communicate with a device. We aim to create a bidirectional SPI to I²C converter which allows SPI devices to communicate with other devices utilizing its I²C bus. Since it is not possible to directly connect SPI with I²C peripherals, our converter will act as an interface to allow data transfer from one device to another at high speeds.

I²C

I²C stands for Inter-Integrated Circuit, originally designed by Philips semiconductors in 1982 [1]. It can be described as a bus interface connection protocol that is included in devices for the purpose of serial communication. It’s a widely used protocol for short-distance communication. The I²C protocol is a two-wire serial interface, also known as a bidirectional wire interface. I²C communication requires two wires or pads: SDA and SCL. SDA is the serial data line and SCL is the serial clock line. The SDA is a bidirectional line that is used to share data between the master and slave. The SCL line carries the clock signal. The master generates and controls the SCL line. The master can be used to communicate with multiple slaves [2].

SPI

SPI stands for Serial Peripheral Interfaces, originally designed by Motorola in 1979 [3]. SPI is a synchronous serial communication interface that is used for short-distance communication.   SPI operates at Full Duplex, which means that it has two different lines for input and output. As a result, data can be received and transmitted at the same time. SPI supports a single master multi-slave configuration. SPI is also known as a four-wired interface, including SCLK, MOSI, MISO, and SS.  SPI operates in Master-Slave architecture in which the device initializing the clock (SCLK) becomes the master. MOSI (Master out Slave in) is the data line carrying data from master to slave. MISO (Master in Slave out) is the data line carrying data from slave to master. SS (Slave Select) is the signal from the master to select the slave, this line is active low and is turned high to disconnect the slave from the SPI bus [4].

Proposed Solution/Circuit: Bi-Directional I²C-SPI Converter

Our proposed solution is to make a bi-directional I²C-SPI converter for on-chip communication. A protocol converter is capable of converting the standard communication (e.g I²C) of one device in order to make it suitable for communication (e.g SPI) with another device. It has the ability to transmit data between two different communication standards. For our proposal, we make two converter: I²C to SPI and SPI to I²C These two will work together as bi-directional I²C-SPI converters as shown in Figure 1.  

Figure 1: I²C to SPI Bi-Directional Converter

When the chip enable is zero the proposed architecture is SPI to I²C converter. The converter will have one SPI master and an I²C slave. The input to the converter will be the MISO, MOSI, SS, and SCLK from the SPI master controller. The converter will convert these signals to be suitable for I²C communication. The output from the controller will be SDA and SCL and they will be fed to the I²C slave [5].

Figure 2: SPI to I²C converter

When the chip enable is one the proposed architecture is I²C to SPI converter. The input to the converter will be the SDA and SCL from the I²C master controller. The converter will convert these signals to be suitable for SPI communication. The output from the converter will be SCLK, MOSI, MISO, and SS_N, which will be fed to the SPI Slave controller [6].

Figure 3: I²C to SPI converter

References

[1] Y. Duan, “I2C data transfer program design and communication protocol improvement,” Lecture Notes on Wireless Networks and Communications, vol. 1, no. 1, pp. 1–16, 2018, doi: 10.23977/lnwnc.2018.11001.

[2] F. Leens, “An introduction to I2C and SPI protocols,” IEEE Instrumentation & Measurement Magazine, vol. 12, no. 1, pp. 8–13, Feb. 2009, doi: 10.1109/mim.2009.4762946.

[3] Shaik. Fazil. Ahmed and Y. Murali, “Implementation Of I2c Multi Task And Multi Slave Bus Controller Using Verilog,” International Journal Of Engineering And Computer Science, Aug. 2015, doi: 10.18535/ijecs/v4i8.61.

[4] X. C. Tian, J. Li, Y. B. Fan, X. N. Yu, and J. Liu, “Design and Implementation of SPI Communication Based-On FPGA,” Advanced Materials Research, vol. 291–294, pp. 2658–2661, Jul. 2011, doi: 10.4028/www.scientific.net/amr.291-294.2658.

[5] B. Jayaramudu, “Implementing Communication Bridge between I2C and AHB,” International Journal for Research in Applied Science and Engineering Technology, vol. 6, no. 5, pp. 2254–2259, May 2018, doi: 10.22214/ijraset.2018.5367.

[6] T. M. L. del Río, L. N. Oliva Moreno, and A. G. Juárez Gracia, “Implementation of the communication protocols SPI and I2C using a FPGA by the HDL-Verilog language,” Research in Computing Science, vol. 75, no. 1, pp. 31–41, Dec. 2014, doi: 10.13053/rcs-75-1-3.

Team Lead:

Hareem Rashid (i180895@nu.edu.pk)                            (FAST-NUCES)

TEAM MEMBERS:

Engr. Ali Sabir                                                                 (FAST-NUCES)

Syeda Zoha Haider                                                         (FAST-NUCES)

Rohail Ahmed                                                                 (FAST-NUCES)

M Usman Kiani                                                               (FAST-NUCES)

Muhammad Bilal                                                            (FAST-NUCES)

Muhammad Awais Butt                                                  (FAST-NUCES)

Dr. Hassan Saif                                                               (FAST-NUCES)