Some Problems Encountered in Using I/O Ports to Simulate IIC Bus Protocol

A recent project is a sensor system based on IIC bus communication. Since another sensor uses a similar IIC protocol instead of standard IIC, the MCU cannot communicate with it. In the end, there is no other way but to implement IIC bus communication through I/O port simulation. The specific program has been posted in my blog earlier. If you are interested, you can check my blog.

Mainly end the problems I encountered in this process

1. No response signal after writing data (instructions or addresses)

The general start timing can be easily written according to the timing diagram in the manual. If there is no response at the first time, it is possible that the data is written to the slave device. Generally, the main thing to check at this time is the rising edge and the falling edge. See if the manual says it is read and written on the rising edge or the falling edge. In my project, the rising edge reads and writes data. In other words, the level indication on the SDA line is read and written at the rising edge; the data is changed at the falling edge. One thing to note is that the SCL line is pulled down first to generate a falling edge. There should be a certain delay after pulling it down in the program, because it takes a certain amount of time for the I/O port to stabilize the level. Otherwise, when SDA is high, if SCL is pulled low by mistake, a start condition will be generated, and the write operation will naturally fail.
2. The data is incorrect when reading data. In
this case, there is data but it is not valid data. Generally, at this time, it is necessary to check whether the simulation timing is correct. It is necessary to clearly read the data at the rising edge, and then pay attention to the data shift. After reading each bit of data, one data bit must be shifted. The following is a code for reading 8 bits of data.

for(i=0;i<8;i++)
{
IIC_SCL_HIGH(); //Conversion completed, SLAVE device pulls the data line low, the clock line generates a rising edge to read the high 8-bit data
REC1=(REC1<<1)+IIC_SDA;
delay_us(5);
IIC_SCL_LOW(); //Pull the clock line low and wait for the next rising edge to arrive
delay_us(5);
}

3. How to write high and low levels in the process of using I/O operations
The input and output I/O ports have directions, so pay attention to the direction of writing. The recommended writing method is to configure the I/O as input when writing high levels, so that the pull-up effect will output a high level to the bus. The advantage of this is that you can wait for the operation of the bus from the device after writing, and there will be no certain conflicts. The following is a high-ground level writing method

#define IIC_SCL_HIGH() IIC_SCL_DIR = PORT_INPUT //Pull the clock line high
#define IIC_SCL_LOW() IIC_SCL_DIR = PORT_OUTPUT; IIC_SCL=0//Pull the clock line low
#define IIC_SDA_HIGH() IIC_SDA_DIR = PORT_INPUT //Pull the data line high
#define IIC_SDA_LOW() IIC_SDA_DIR = PORT_OUTPUT; IIC_SDA=0//Pull the data line low