LPC2148 I2C Programming Tutorial

In this tutorial we will go through LPC2148 I2C programming and learn how to program it for interfacing various I2C modules, sensors and other slave devices. For those who are new to I2C Bus & Protocol I have posted an I2C Basics Tutorial @ http://www.ocfreaks.com/i2c-tutorial/

Introduction

A quick Recap of I2C

I2C was invented by Philips in 1980s. I2C stands for Inter-Integrated Circuit and also sometimes also referred as TWI i.e. Two Wire Interface since it uses only 2 wires for data transmission and synchronization. The two wires of I2C Bus consists of:
1. Data Line which is SDA i.e. Serial Data
2. Clock Line which is SCL i.e. Serial Clock

I2C uses 7bit and 10bit addresses for each device connected to the bus. 10bit addressing was introduced later. In this tutorial we will use 7bit addressing since its common with sensors, eeproms, etc. A general I2C bus topology with multiple masters and multiple slaves connected to the bus at the same time is shown below:

I2C bus is a Byte Oriented bus. Only a byte can be transferred at a time. Communication(Write to & Read from) is always initiated by a Master. The Master first sends a START condition and then writes the Slave Address(SLA) and the Direction bit(Read=1/Write=0) on bus and the corresponding Slave responds accordingly.

Format for I2C communication protocol is given as:

I2C module in LPC2148 ARM7 Microcontrollers

The I2C block in LPC2148 and other LPC2100 series ARM7 MCUs can be configured as either Master, Slave or both Master & Slave. It also features a programmable clock which aids in using different transfer rates as required. The I2C block in LPC214x supports speeds up to 400kHz.

I2C has 4 operating modes:

1. Master Transmitter mode
2. Master Receiver mode
3. Slave Transmitter mode
4. Slave Receiver mode

LPC2148 ARM7 Microcontroller supports all of these 4 modes, but in this tutorial we will go through Master Transmitter and Master Receiver modes only since implementing the Slave modes is easy once you understand the Master modes and also since Master mode is used for interfacing with Sensors, LCD Displays, and other I2C slave devices.

Registers used for programming LPC2148 I2C block

Before we get into Operating mode details lets go through the registers used in I2C block of LPC214x:

(Replace 0 with 1 for I2C1 block registers)

LPC2148 I2C Status Codes

Before we start coding, first lets go through some status codes. Whenever an event occurs on the I2C bus a corresponding I2C status code will be set in I2CxSTAT register.

I2C Master Modes in LPC2148 ARM7 MCU:

I2C Master Transmitter Mode:

To enter the Master Transmitted mode we set the STA bit to 1. After this the master will output a START condition(as soon as the bus is free) and the first byte is sent on the bus that will contain the address(7 bits) of the slave device along with the R/W bit. Here we set the R/W to 0 which means Write. After this the data sent a byte at a time. For each byte sent by master, the slave device sends a corresponding Acknowledgement bit(AA=0). When slave is finished sending data or has no more data to send it will send a ‘Not Acknowledge'(AA=1) bit to indicate this. After this the master outputs a STOP condition. This is shown the figure below:

I2C Master Receiver Mode:

In this mode a slave transmitter sends data to a Master Receiver. The initialization is same that we saw for Master Transmitter above, except here we set the R/W bit to 1 which means Read. The slave acknowledges it and sends data byte(s). For each byte sent by slave, the master device sends a corresponding Acknowledgement bit(AA=0). If master wants to continue it can send an Acknowledge bit to salve or if master want to stop receiving data it will send a ‘Not Acknowledge'(AA=1) bit to indicate this. After this master will output a STOP condition. This is shown the figure below:

Procedure for I2C communication in Master Transmitter Mode:

Procedure for I2C communication in Master Receiver Mode:

LPC2148 I2C ARM7 Setup & Programming

In order to communicate with any I2C device we need to set the I2C clock frequency. The I2C Clock/bit frequency is set using 2 registers: I2CxSCLH and I2CxSCLL. I2CxSCLH defines the number of PCLK(Peripheral Clock) cycles for the I2C Clock(SCL) High time while I2CxSCLL defines the number of PCLK cycles for the I2C Clock(SCL) Low time. It is given a simple formula as given below :

Note that LPC214x ARM7 Microcontrollers support a maximum I2C frequency of 400KHz. In our case we will use a frequency of 100KHz. Given our PCLK is running at 60Mhz we need to set I2C0SCLH = I2C0SCLL = 300 for IC20 Module.

Now lets, define some bits which will help us setup the I2C0ONCLR and I2C0CONSET registers to initialize the I2C0 block before we can use it.

#define I2EN (1<<6) //Enable/Disable bit
#define STA  (1<<5) //Start Set/Clear bit
#define STO  (1<<4) //Stop bit
#define SI   (1<<3) //Serial Interrupt Flag Clear bit
#define AA   (1<<2) //Assert Acknowledge Set/Clear bit

Now, we will define some basic ‘building block’ functions which will help us in programming the I2C module without complicating it too much.

1. I2C initialization function – I2C0Init(): It first select the I2C function of the respective pins. Then it configures the I2C bit rate(I2C bus clock), clears I2C0CONCLR register and then finally enables the I2C0 block using I2C0CONSET register.

void I2C0Init(void) 
{
	PINSEL0 |= (0<<7)|(1<<6)|(0<<5)|(1<<4); //Select SCL0(P0.2) and SDA0(P0.3)
	I2C0SCLL = 300;
	I2C0SCLH = 300; //I2C0 @ 100Khz, given PCLK @ 60Mhz
	I2C0CONCLR = STA | STO | SI | AA; //Clear these bits
	I2C0CONSET = I2EN; //Enable I2C0
	//After this we are ready to communicate with any other device connected to the same bus.
}

2. SI wait function – I2C0WaitForSI(void): This functions waits for the SI bit to be set after any action taken by the I2C hardware. When this bit is set it indicates that the action taken by I2C module has been completed i.e. a new event has occurred which in turn changes the status code in I2C0STAT.

bool I2C0WaitForSI(void) //Wait till I2C0 block sets SI
{
	int timeout = 0;
	while ( !(I2C0CONSET & SI) ) //Wait till SI bit is set. This is important!
	{
		timeout++;
		if (timeout > 10000) return false; //In case we have some error on bus
	}
	return return; //SI has been set
}

3. Send START/Repeat-START function – I2C0SendStart(): This functions sends a START condition as soon as the bus becomes free =or= sends a Repeat START is already in master mode and then waits till SI bit set.

void I2C0SendStart(void)
{
	I2C0CONCLR = STA | STO | SI | AA; //Clear everything
	I2C0CONSET = STA; //Set start bit to send a start condition
	I2C0WaitForSI(); //Wait till the SI bit is set
}

4. Send STOP Function – I2C0SendStop(): This function sends a STOP condition and then waits for the STO bit in I2C0CONSET to auto clear which indicates was sent on the bus.

void I2C0SendStop(void)
{
	int timeout = 0;
	I2C0CONSET = STO ; //Set stop bit to send a stop condition
	I2C0CONCLR = SI;
	while (I2C0CONSET & STO) //Wait till STOP is send. This is important!
	{
		timeout++;
		if (timeout > 10000) //In case we have some error on bus
		{
			printf("STOP timeout!\n");
			return;
		}
	}
}

5. I2C Transmit Byte function – I2C0TX_Byte(unsigned char): This function sends a byte on the I2C bus and then waits for SI to be set.

void I2C0TX_Byte(unsigned char data)
{
 	I2C0DAT = data;
	I2C0CONCLR = STA | STO | SI; //Clear These to TX data
	I2C0WaitForSI(); //wait till TX is finished
}

6. I2C Receive Byte function – I2C0RX_Byte(bool):

unsigned char I2C0RX_Byte(bool isLast)
{
	if(isLast) I2C0CONCLR = AA; //Send NACK to stop; I2C block will send a STOP automatically, so no need to send STOP thereafter.
	else 	     I2C0CONSET = AA; //Send ACK to continue
	I2C0CONCLR = SI; //Clear SI to Start RX
	I2C0WaitForSI(); //wait till RX is finished
	return I2C0DAT;
}

Now armed with the I2C communication building block functions we can interface LPC2148 in Master Transmitter or Master Receiver mode with any slave device.

LPC2148 I2C Example: Interfacing 24LC64 EEPROM

Now, lets do an I2C programming example where we Write and Read to an EEPROM. I’ll be using 24LC64 for this example. Make sure you refer its datasheet- just in case 😉

Here is the connection diagram between LPC2148 Microcontroller and EEPROM:

In order to Read and Write to EEPROM we will define 1 macro and 2 functions as follows:

1. checkStatus(int) Macro function: This functions checks if the current value in I2C0STAT is same as argument supplied to. If not it will send STOP condition and make the calling function return false which indicates an error condition.

#define checkStatus(statusCode) \
if(I2C0STAT!=statusCode) \
{ \
	printf("Error! Expected status code: %i(decimal), Got: %i(decimal)\n",statusCode,I2C0STAT); \
	I2C0SendStop(); return false; \
}

2. I2C0WriteEEPROM(…) function: This writes data from buffer to the I2C slave device. It takes 3 arguments : startDataAddress – the starting address inside EEPROM where the writes must begin from , data – a pointer to data buffer which contains data to be written to eeprom, length – length of the data buffer.

/*(C) Umang Gajera | Power_user_EX - www.ocfreaks.com 2011-17. LPC2148 I2C Tutorial
More Embedded tutorials @ www.ocfreaks.com/cat/embedded*/
bool I2C0WriteEEPROM(unsigned int startDataAddress, unsigned char *data, int length)
{	
	for(int count=0 ; count< length ; count++ ) { I2C0SendStart(); //Send START on the Bus to Enter Master Mode checkStatus(0x08); //START sent I2C0TX_Byte(I2CSlaveAddr & 0xFE); //Send SlaveAddress + 0 to indicate a write. checkStatus(0x18);//SLA+W sent and ack recevied I2C0TX_Byte((startDataAddress & 0xFF00)>>8); //Send Word Address High byte first. (24xx64 needs 2 word address bytes)
		checkStatus(0x28); //High byte has been sent and ACK recevied

		I2C0TX_Byte(startDataAddress & 0xFF); //Now send the Low byte of word Address
		checkStatus(0x28); //Low byte has been sent and ACK recevied

		I2C0TX_Byte(data[count]); //Finally send the data byte.
		checkStatus(0x28); //Data Byte has been sent and ACK recevied

		startDataAddress++; //Increment to next address
		I2C0SendStop(); //Send STOP since we are done.
		
		//Now initiate write acknowledge polling as given on page 9 of 24LC64's datasheet
		const int retryTimeout = 100;
		for(int i=0; i < retryTimeout; i++)
		{
			I2C0SendStart();
			checkStatus(0x08);
			I2C0TX_Byte(I2CSlaveAddr & 0xFE);
			if(I2C0STAT == 0x18) //ACK recieved which indicates completion of write cycle
			{
				I2C0SendStop();
				//printf("Write Completed! for data = %c\n",data[count]);
				goto OUT;
			}
			I2C0SendStop();
		}
		I2C0SendStop();
		printf("Warning: Write Poll Timeout! for data = %c\n",data[count]);

		OUT:; //Get us out of the loop.
	}
	return true;
}

3. I2C0ReadEEPROM(…) function: This reads data to buffer from the I2C slave device. Arguments are similar to those of I2C0WriteEEPROM();

/*(C) Umang Gajera | Power_user_EX - www.ocfreaks.com 2011-17. LPC2148 I2C Tutorial
More Embedded tutorials @ www.ocfreaks.com/cat/embedded*/
bool I2C0ReadEEPROM(unsigned int startDataAddress, unsigned char *data , int length)
{ 
	unsigned char RXData = 0;
	for(int i=0; i < length;i++) { I2C0SendStart(); //Send START on the Bus to Enter Master Mode checkStatus(0x08); //START sent I2C0TX_Byte(I2CSlaveAddr & 0xFE); //Send SlaveAddress + 0 to indicate a write. checkStatus(0x18);//SLA+W sent and ACK recevied I2C0TX_Byte((startDataAddress & 0xFF00)>>8); //Send Word Address High byte first. (24xx64 needs 2 word address bytes)
		checkStatus(0x28); //High byte has been sent and ACK recevied

		I2C0TX_Byte(startDataAddress & 0xFF); //Now send the Low byte of word Address
		checkStatus(0x28); //Low byte has been sent and ACK recevied

		startDataAddress++; //Increment to next address		

		I2C0SendStart(); //Send Repeat START, since we are already in Master mode
		checkStatus(0x10); //Repeat START sent

		I2C0TX_Byte(I2CSlaveAddr | 0x01); //This makes SLA-RW bit to 1 which indicates read.
		checkStatus(0x40); //SLA-R has been Transmitted and ACK received.

		if(i != length-1)	RXData = I2C0RX_Byte(false); //Send NACK for last byte to indicate we want to stop
		else RXData = I2C0RX_Byte(true); //Send ACK for byte other than last byte to indicate we want to continue.
		
		data[count++] = RXData; //Write recieved data to buffer
		printf("Data='%c' ",RXData);
		
	}
	return true;
}

Finally here is the code for main() function:

/*(C) Umang Gajera | Power_user_EX - www.ocfreaks.com 2011-17. LPC2148 I2C Tutorial
More Embedded tutorials @ www.ocfreaks.com/cat/embedded*/
#include <lpc214x.h>
#include "ocfreaks_sh.h" //This contains code for UART, printf(), initClocks()
#include <stdint.h>

#define I2EN (1<<6) //Enable/Disable bit
#define STA  (1<<5) //Start Set/Clear bit
#define STO  (1<<4) //Stop bit
#define SI   (1<<3) //Serial Interrupt Flag Clear bit
#define AA   (1<<2) //Assert Acknowledge Set/Clear bit

void I2C0Init(void);
bool I2C0WaitForSI(void);
void I2C0SendStart(void);
void I2C0SendStop(void);
void I2C0TX_Byte(unsigned char data);
unsigned char I2C0RX_Byte(int isLast);

bool I2C0ReadEEPROM(unsigned int addresss, unsigned char *data, int length);
bool I2C0WriteEEPROM(unsigned int address, unsigned char *data, int length);

unsigned char I2CSlaveAddr = 0xA0; //Address of EEPROM (A2=0,A1=0,A0=0)

int main(void)
{
	initClocks();
	initUART0();
	I2C0Init();

	printf("(C) ocfreaks.com - LPC2148 I2C tutorial.\nExample: Interfacing 24LC64 EEPROM.\n\n");
	
	#define BUFF_SIZE 30 //29 Characters + 1 Termination Character = 30 Total
	unsigned char bufferWrite[BUFF_SIZE] = "www.ocfreaks.com I2C Tutorial"; 
	unsigned char bufferRead[BUFF_SIZE] = {0};

	//Write data from bufferWrite to EEPROM
	printf("Writing data to EEPROM... \n");
	if( !I2C0WriteEEPROM(0,bufferWrite,BUFF_SIZE) )
	{
		printf("Writing Error!\n");
	}
	printf("Write finished!\n\n");

	//Read EEPROM Data into bufferRead
	printf("Reading data from EEPROM: \n");
	if( !I2C0ReadEEPROM(0,bufferRead,BUFF_SIZE) )
	{
		printf("Reading Error!\n");
	}

	printf("\n\nData bytes recevied are as follows:\n");
	printf("\"");
	for(int i=0; i < BUFF_SIZE; i++)
	{
		printf("%c",(char)bufferRead[i]);
	}
	printf("\"");
	printf("\n\nDone!\n");
	
	while(1); //Loop infinitely.
	return 0; //Normally, this won't execute.
}

Serial Output:

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