i2c protocol software implementation

[Fan174]

Good evening to all

There are so many document's available on the internet for I2C communication and I have spend hard time to understand I2C software protocol

I am not looking for any code. I want to understand how does it work so I made one flow chart that explain my understanding

I have attached PDF file and I am looking one guide who can help me with my flow chart.

 

[KlausST]

Hi,

This is not a general I2C communication flow chart.

It as a dedicated DS1307 I2C communication.
Thus please refer to the DS1307 datasheet. There are three figures (4, 5 and 6). Please say which one you want to implement. Then compare them step by step with your flow chart.

There are mistakes. But you did a good job. Drawing the flow chart is the best way to really understand the interface.
I also like your naming:
"Generate" is a bit manipulating process
"Send" is an 8 bit shift process (I´m not sure you are aware of this, because of the right bottom part)
"Get" is a one bit read process

Confusing is the right bottom part. With "i<7"...
Here - I think - is a mistake. I can just guess that this should be the inner loop of the "send" process.

Also note:
* In the DS1307 datasheet figures there is only one "I2C Start" per figure, but your flow chart includes three "I2C Start" procedures.
* At "data write" procedures the SLAVE needs to set ACK.
* At "data read" procedures the MASTER needs to set ACK except the last one. --> you additionally need to implement "SET ACK"

***
To prevent you from the most often made I2C implementation mistake:
Mind: I2C never sets an output HIGH. A HIGH is generated by an external pullup resistor and the I/O set to HIGH_IMPEDANCE.
Valid output states: DRIVE_LOW or HIGH_IMPEDANCE.

Klaus

 

[Fan174]

Hi,

This is not a general I2C communication flow chart.

It as a dedicated DS1307 I2C communication.
Thus please refer to the DS1307 datasheet. There are three figures (4, 5 and 6). Please say which one you want to implement. Then compare them step by step with your flow chart.

@KlausST I am really sorry for not defining title clearly. I am not very good in english. I want to learn i2C bit banging

I want to implement figure 6.

Hi,There are mistakes. But you did a good job. Drawing the flow chart is the best way to really understand the interface.

.

Thanks for encourage me to make flow chart. There are the different opinion in every link I will look each problem step by step

so can you point my some mistake so I can improve flow chart

 

[FvM]

Your flowchart is wrong. It generates new start with register address, however start has to be send exclusively before the slave address.

I suggest to refer to the original Philips/NXP I2C specification. **broken link removed**

 

[KlausST]

Hi,

How I´d check it step by step:

Klaus

 

[Fan174]

Your flowchart is wrong. It generates new start with register address, however start has to be send exclusively before the slave address.

I suggest to refer to the original Philips/NXP I2C specification. **broken link removed**

I saw datasheet and I am making flow chart for figure 9

I have attached new flow chart

Does it match with figure 9 ?

- - - Updated - - -

Hi,

How I´d check it step by step:

Klaus

I have modified flow chart according to figure 6

I don't understand if I get Ack How to read data n to Data n+x

Please see my Flow chart I2C 4

 

[srizbf]

Get philips(nxp) AN10216.pdf. The proper protocol is given on page. 11.
Make a flowchart for the specified one.

 

[Fan174]

Hi,

How I´d check it step by step:

Klaus

@KlausST I need your help,

I do not understand how to implement below in flow chart

DATA TRANSFERRED (X+1 BYTES + ACKNOWLEDGE); NOTE: LAST DATA BYTE IS FOLLOWED BY A NOT ACKNOWLEDGE (A) SIGNAL)

My flow chart is incomplete, after ACK I have to read many bytes how to do that

 

[KlausST]

Hi,

Reading an 8 bit wide "data" byte is similar to
outputting an 8 bit "word address" or sending the 8bit "slave address + R/W".

it is a loop running 8 times per byte: like this.
* n= 8
Loop:
* SCL = 0
* wait (during this phase the master or slave OUTPUTS data)
* SCL = 1
* wait
* READ state of SDA = data bit "n-1 of a byte" (MSB first)
* n = n -1
if n>= 0 goto LOOP
(now you have 8 bits = 1 byte read)
***
then you have to do the 9´th bit communication for ACK
***

run this for as many bytes you want to read.

***************************
wait time: if you want about 400kHz bit rate, then one bit time is 2.5us. Since you have two waits per bit the wait time should be about 1.25us

******
refer to UM10204, Fig 38 for timing.
refer to UM10204, Fig 5 for SDA and SCL sates

******
Mind
* idle sate is: SCL = 1 and SDA = 1
* Before performing an "I2C_START" be sure that the bus is in idle sate. If it is not in idle state: perform an "I2C_STOP" before the "I2C_START"
* A single bit communication starts with SCL=1 and ends with SCL=1. This is also true for a ACK communication ans well as a 8 bit data communication.
* to end a communication always perform an I2C_STOP

Klaus

 

[Fan174]

Hi,

Reading an 8 bit wide "data" byte is similar to
outputting an 8 bit "word address" or sending the 8bit "slave address + R/W".

it is a loop running 8 times per byte: like this.

Klaus

Thanks Klaus, That's excellent explanation

I have modified my flaw chart to read many bytes @KlausST Please see attached flow diagram

I am not very good at Embedded c programming.

This is my attempt to store the byte using array pointer in c language

#include<stdio.h>

int main(void)
{
    int array[8]= {5, 4, 6, 8, 9, 7, 8, 8};
	
    int *pointer = &array[0];
    
	int i;
  
    for( i = 0; i < 8; i++ )
        printf("\n Array[%d] is %d ",i,*(pointer+i));
   
    
	for( i = 0; i < 8; i++)
        printf("\n %d at %u ",*(pointer+i),(pointer+i));
   
    return 0;
}

Output of code

Array[0] is 5
Array[1] is 4
Array[2] is 6
Array[3] is 8
Array[4] is 9
Array[5] is 7
Array[6] is 8
Array[7] is 8

5 at 6422280
4 at 6422284
6 at 6422288
8 at 6422292
9 at 6422296
7 at 6422300
8 at 6422304
8 at 6422308

 

[KlausST]

Hi,

you forgot about ACK after each byte.
I now marked it red in my post#9
Please read the recommended documents.

I am not very good at Embedded c programming.

I´can read a bit, but can't write at all....


Klaus

 

[Fan174]

Hi,

you forgot about ACK after each byte.
I now marked it red in my post#9
Please read the recommended documents.

Klaus

Please take a look at new flow chart. I have added Ack after each byte. Let me know if I am making mistake somewhere

Hi,
I´can read a bit, but can't write at all....

Klaus

I understand I am making flow chart to understand basic first. Once I complete flow chart then I will try to convert it into program

 

[FvM]

Correct, except for: You are reading 9 bytes instead of 8. And you miss to generate the NACK after last byte.

 

[Fan174]

Correct, except for: You are reading 9 bytes instead of 8. And you miss to generate the NACK after last byte.

Thanks for pointing mistake

see the new flow chart Does it look's okay

 

[FvM]

Looks good now

 

[Fan174]

Looks good now

Then I would try next step. I have to write code for each box in flow chart

according to Datasheet AN10216-01 I2C

START and STOP Conditions

START: A HIGH to LOW transition on the SDA line while SCL is HIGH

STOP: A LOW to HIGH transition on the SDA line while SCL is HIGH

pseudo code : This code will not compile and run. It's just for understanding

SDA        PIN1

SCL        PIN2  

define High  1

define Low   0

void Generate_I2C_Start ();    //Declare the function  

void Generate_I2C_Stop ();    //Declare the function  

void main (void)   //start from here 
{
     while (1)  //infinite Loop
   {
        Generate_I2C_Start ();  //generate i2c start conditions 
   }
}

according to this A HIGH to LOW transition on the SDA line while SCL is HIGH

What would be routine Generate_I2C_Start (); ?

 

[FvM]

Which processor are you working with?

Driving SCL or SDA to high level is done by tri-stating the port pin. Except for peripherals with open drain pin like 8051 this needs programming the direction register.

---

Code C - [expand]
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// assumed state before start
SDA = Z;
SCL = Z;
// Generate start
SDA = 0;
delay;
SCL = 0;
delay;

---

 

[Fan174]

Which processor are you working with?

Driving SCL or SDA to high level is done by tri-stating the port pin. Except for peripherals with open drain pin like 8051 this needs programming the direction register.

Hi FvM,

I would prefer 8051

This is new version of pseudo code It's little bit different then the original flow chart

---

Code C - [expand]
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#define SDA P2_1        /* Set P2.1 = SDA */
#define SCL P2_2        /* Set P2.2 = SCL */
 
define High  1
 
define Low   0
 
void I2C_Initialize (void)     //Declare the function
void I2C_Delay (N)             //Declare the function
void Generate_I2C_Start ();    //Declare the function  
 
void Generate_I2C_Stop ();    //Declare the function  
 
void main (void)   //start from here 
{
     while (1)  //infinite Loop
     
   {
        I2C_Initialize ();     //  idle sate is: SCL = 1 and SDA = 1
        Generate_I2C_Start ();  //generate i2c start conditions 
   }
}
 
// This function give N nuber of delay 
void I2C_Delay(int N)      
{
    unsigned int i;
 
    for( i= 0; i < N; i++);
}
 
// Initialize idle sate is: SCL = 1 and SDA = 1
void I2C_Initialize (void) 
 
{
     SCL = 1   // set SCL pin to High
     SDA = 1   // Set SDA pin to High 
}
 
//generate i2c start conditions 
void Generate_I2C_Start (void)
{
    SDA = Low;  // Clear SDA Pin
    I2C_Delay(2);  //Required delay
    SCL = Low;   // Clear SCL Pin
    I2C_Delay(2);  //Required delay
}

---

 

[KlausST]

Hi,

please don´t get sloppy now. Stay focussed. Read our posts.

from post#2:

To prevent you from the most often made I2C implementation mistake:
Mind: I2C never sets an output HIGH. A HIGH is generated by an external pullup resistor and the I/O set to HIGH_IMPEDANCE.
Valid output states: DRIVE_LOW or HIGH_IMPEDANCE.

from post#9:

* Before performing an "I2C_START" be sure that the bus is in idle sate. If it is not in idle state: perform an "I2C_STOP" before the "I2C_START"

Klaus

 

[Fan174]

@KlausST , @FvM

I am still stuck to convert block into coding. Can you give some hint's how to go for further process