How to use Arduino in SPI 3-wire ?

Using Arduino Networking, Protocols, and Devices
1

When SPI were used in 4-wire mode, one should write dummy bytes in MOSI as it receiving bytes in MISO, how about 3-wire mode?

2

That depends on the configuration and which end of the bus the device is. Check this link, it should explain what you need to know.
Introduction to SPI Interface | Analog Devices Then there is this one: Interfacing a DS1868 3-Wire Device to a SPI Bus | Analog Devices

3

Please, mention the types of Arduino and slave device.

4

Arduino UNO + ADXL345

5

I read these 2, they didn't give code details.

6

1. Are you using raw sensor (Fig-1) or a breakout board (Fig-2). If using breakout board, please post the picture as there are varieties of breakout boards.

ADXL345RawChip
Figure-1:

image
Figure-2:

2. Why do you want to use 3-Wire SPI Port when there are enough pins for the UNO to handle 4-WIre SPI?

7
8

Can you please answer to my Question-1 of post #6. It is importaant for me to guide you.

9

I used a breakout board:

ADXL345
ADXL345800×800 49.9 KB

It's circuit diagram:
ADXL345_module
ADXL345_module750×423 31 KB

1 Like
10

1. The schematic does not agree with the signal signatures of your board. Please, show your connection like this:

ADXL345      UNO
5V           5V
3V3          where?
GND          GND
VS           where?
CS           where?
IN1          where?
IN2          where?
SDO          where?
SDA          where?

2. Are you using a Library for the operation of ADXL345? If yes, mention the name of the Library.

3. Please, post the codes/sketch that you have tried.

11

Surprise you never mentioned you wanted code which you will find in examples under the IDE files menu.

1 Like
12

Notice that OP is not responding to post #10. I am in doubt if he has the gadgets or he is just simulating.

13

You two didn't understand my question, I want to know the difference in code reading and writing between spi 4-wire mode and 3-wire mode.

14

Do you have breakout board and UNO? If yes, I will provide you now to do the functional check of the sensor/breakout board using I2C Bus. After that it will be your task to operate the board:
1. Using 4-Wire SPI Port
2. Usin 3-Wire SPI Port.

15

The board has both IIC and SPI interface, I have used IIC mode, now I want to use SPI, and its default mode is SPI 3-wire. I want you guide me in writing code for reading and writing in SPI 3-wire mode.

17

Let me know the I2C Slave address of your sensor and the x, y, z components of g that you have got. Is the breakout board a 3.3V device or 5V device?

18

@MianQi
You can't do the ADXL345 3 wire SPI on an Uno using hardware SPI.

19

No it's 4 wire

20

Why not?

The data sheets clearly says that storing HIGH (1) into bit-6 of DATA_FORMAT register puts the sensor into 3-Wire SPI Mode. Now, the user has to wrie codes to chnage the directions of SDIO Line (SDA on Breakout Board) as input/output when necessary.
ADXL345.pdf (481.8 KB)

21

The sensor supports 4-WIre SPI, 3-Wire SPI, and I2C. There is no default mode as the value of SPI-bit in the DATA_FORMAT Register is unspecified. The concern is the Breakout Board to see how have they configured the sensor pins (Figure of post #9).

I would say that the default mode is I2C. You just connect the SDA/SCL pins of the breakout board with SDA/A4 and SCL/A5 lines of UNO. The board just works on Wire.h based sketch of IDE Example.
sensortest-1.ino (4.4 KB)

1 Like