I 2 C Communication. Embedded Systems Interfacing. 25 October 2011

Transcription

1 25 October 2011

2 frametitletypical System

3 Specifications Version Up to 400 Kbps 10 bit addresses Version Up to 3.4 Mbps New signal levels for High-speed operation Version Some timing conditions relaxed SMBus Version 2.0 Relaxed version of I2C specification for power management (10 Kbps to 100 Kbps)

4 Terminology Transmitter: device that sends data to the bus Receiver: device that accepts data from bus Master: device which initiates a transfer, generates clock and terminates transfer with NAK Slave: device addressed by master Multi-master: more then one device attempts control of bus at one time without corrupting message

5 Terminology (cont d)

6 Terminology (cont d) Arbitration: procedure to ensure that, if more than one master simultaneously tries to control the bus, only one is allowed to do so and the winning message is not corrupted Synchronization: procedure to synchronize the clock signals of two or more devices

7 Signal Levels A pull-upresistor is used On a float (or high) the resistor dissipates no current, so the signal is high On a low, the line is brought to ground and the resistor dissipates current This allows connection of 5V with 3.3V devices.

8 I 2 C Master Mode Initialization void I2Cinit(int BRG, unsigned char addrmode) int temp; I2C1BRG = BRG; //BRG=0x27 for Fosc=8Mhz,SCK 100kHz I2C1CONbits.I2CEN = 0; // Disable I2C Mode I2C1CONbits.DISSLW = 1; // Disable slew rate control IFS1bits.MI2C1IF = 0; // Clear Interrupt I2C1CONbits.I2CEN=1; // start module; configure SDA & SCK if (addremode==10) I2C1CONbits.A10M=1; //set 10-bit address mode else I2C1CONbits.A10M=0; //set 07-bit address mode temp = I2CRCV; // read buffer to clear buffer full reset i2c bus(); // set bus to idle //initi2c

9 Master Messageing Transmission Set the SEN bit (Start event) Write the I2CxTRN register (Master tranmission) sending the peripheral address and W (R/W clear) Wait for ACK (acknowledge) Write the I2CxTRN register, sending the message byte Wait for ACK Set the PEN bit (Stop event) Receiving Set the SEN bit Write the I2CxTRN register, sending the peripheral address and R Wait for ACK Set the RCEN to enable reception Sett ACKEN to start Acknowledge event Set PEN

10 Master Messaging (cont d)

11 Master Messaging (cont d)

12 Master Messaging (cont d)

13 Start Event Routine void I2Cstart(void) int x = 0; I2C1CONbits.ACKDT = 0; //Reset any previous Ack DelayuSec(10); I2C1CONbits.SEN = 1; //Initiate Start condition Nop(); //hardware automatically clears Start Bit, wait for clear while (I2C1CONbits.SEN) DelayuSec(1); x++; if (x > 20) break; DelayuSec(2);

14 Restart Event Routine void I2Crestart(void) int x = 0; I2C1CONbits.RSEN = 1; //Initiate restart condition Nop(); //wait for automatic clear before proceding while (I2C1CONbits.RSEN) DelayuSec(1); x++; if (x > 20) break; DelayuSec(2);

15 void I2Cresetbus(void) int x = 0; //initiate stop bit I2C1CONbits.PEN = 1; //wait for hardware clear of stop bit while (I2C1CONbits.PEN) DelayuSec(1); x ++; if (x > 20) break; I2C1CONbits.RCEN = 0; IFS1bits.MI2C1IF = 0; // Clear Interrupt I2C1STATbits.IWCOL = 0; I2C1STATbits.BCL = 0; DelayuSec(10);

16 Byte Send char I2Csendbyte(int data) int i; while (I2C1STATbits.TBF) IFS1bits.MI2C1IF = 0; // Clear Interrupt I2CTRN = data; // load the outgoing data byte // wait for transmission for (i=0; i<500; i + +) if (!I2C1STATbits.TRSTAT) break; DelayuSec(1); if (i == 500) return(1); // Check for NO ACK from slave, abort if not found if (I2C1STATbits.ACKSTAT == 1) I2Cresetbus(); return(1); DelayuSec(2); return(0);

17 Read Routine char I2Creadrandom(void) int i = 0; char data = 0; //set I2C module to receive I2C1CONbits.RCEN = 1; //if no response, break while (!I2C1STATbits.RBF) i ++; if (i > 2000) break; data = I2CRCV; //get data from I2CRCV register return data;

18 Random Write Function void I2Cwrite(char addr, char subaddr, char value) I2Cstart(); I2Csendbyte(addr); I2Csendbyte(subaddr); I2Csendbyte(value); I2Cbusreset();

19 Random Read Function char I2Cread(char addr, char subaddr) char temp; I2Cstart(); I2Csendbyte(addr); I2Csendbyte(subaddr); DelayuSec(10); I2Crestart(); I2Csendbyte(addr 001); temp = I2Creadrandom(); I2Cresetbus(); return temp;