1. I2C Synchronous Serial Two wire communications (plus ground)
SCL – clock line
SDA – bi-directional data line
Message length: unrestricted
Master – Slave Network
Master
Controls the information flow
Source of SCL
Slave
Can synchronize data transfer by introducing wait states
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2. I2C Synchronous Serial Multi-drop communications:
Multiple transmitters and receivers on a common communications conductor
Broadcast communications is possible
One sender – many listeners
Collision arbitration is required for multiple masters
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3. I2C Definitions TERM DESCRIPTION
Transmitter: The device which sends data to the bus
Receiver: The device which receives data from the bus
Master: The device which initiates a transfer, generates clock signals
and terminates a transfer
Slave: The device addressed by a master
Multi-master: More than one master can attempt to control the bus at the
same time without corrupting the message
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
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4. I2C Physical Layer
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5. I2C Framing
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6. I2C Bit Transfer
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7. I2C Byte Transfer Bit States Recessive (high == 1) Dominate (low == 0)
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8. I2C Acknowledge
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9. I2C Address
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10. I2C Packet
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11. Master Write Packet
NACK – “Not ACKnowldege” can be used by slave to terminate packet
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12. Master Read Packet
Specification calls for Master to terminate with a NACK and a Stop bit
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13. Master Write / Read Packet
If changing direction of data transfer, then the master must resend the address in order to change the value of the R/W bit
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14. “Mystery Code” int ReadIOXPort(unsigned char port) { #define IOX0 0x76
#define I2C_READ 0x01 // R/W bit
char data_byte; int err;
if(!port) // Assign I2C Address to Port Number
port = IOX0; else port = IOX1;
if (err=i2c_start_tx()) { // Start bit
i2c_stop_tx(); return 0xff00 | err; } // Stretching error
if (err=i2c_write_char(port + I2C_READ)) { // Send Address
i2c_stop_tx(); return 0xfe00 | err; } // Stretching error
If (err=i2c_read_char(&data_byte)) { // Read data
i2c_stop_tx(); return 0xfc00 | err; } // Stretching error
i2c_send_ack(); // Acknowledge data
i2c_stop_tx(); // Stop bit
return (unsigned int) data_byte; } // end ReadIOXPort
“Mystery Code”
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15. “Bit Banging” // Define these to change basic bit handling
#define i2c_SCL_H() BitWrPortI(PDDDR,&PDDDRShadow,0,I2CSCLBit) #define i2c_SCL_L() BitWrPortI(PDDDR,&PDDDRShadow,1,I2CSCLBit)
#define i2c_SDA_H() BitWrPortI(PDDDR,&PDDDRShadow,0,I2CSDABit) #define i2c_SDA_L() BitWrPortI(PDDDR,&PDDDRShadow,1,I2CSDABit)
#define i2c_SCL() BitRdPortI(PDDR,I2CSCLBit) // read SCL
#define i2c_SDA() BitRdPortI(PDDR,I2CSDABit) // read SDA
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16. Clock Stretching int i2c_wSCL_H(){ // Tries to set SCL high & waits
// Returns -1 if SCL stretch too long
auto int delay_cnt;
i2c_SCL_H(); cWAIT_5_us; // Set SCL HI
delay_cnt = 0;
while(i2c_SCL()==0 && delay_cnt < i2cClockStretchDelay) {
cWAIT_5_us; delcnt++;
} // end while
if (i2c_SCL()==0)
return -1; // Clock stretch too long
return 0;
} // end i2c_wSCL_H()
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17. Start, Stop, & Ack int i2c_start_tx(){ // Try to send start pulse.
// If clock stretch exceeded, return -1 else 0
if (i2c_wSCL_H()) return -1; // Try to set SCL HI
i2c_SDA_H(); cWAIT_5_us; // Set SDA HI
i2c_SDA_L(); cWAIT_5_us; // Set SDA LO
i2c_SCL_L(); return 0; // Set SCL LO
} // end i2c_start_tx
void i2c_stop_tx() {
i2c_SDA_L(); cWAIT_5_us;
i2c_SCL_H(); cWAIT_5_us;
i2c_SDA_H();
} // end i2c_stop_tx
int i2c_send_ack() {
i2c_SDA_L(); cWAIT_5_us;
if (i2c_wSCL_H()) return -1;
cWAIT_5_us;
i2c_SCL_L(); cWAIT_5_us;
i2c_SDA_H();
return 0;
} // end i2c_send_ack
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18. Write Char int i2c_write_char(char d){
// Writes char; returns -1 if no ACK from remote
auto char i;
for (i=0; I < 8; i++) {
if (d & 0x80) i2c_SDA_H(); // send bit
else i2c_SDA_L();
cWAIT_5_us;
if (i2c_wSCL_H()) return -1; // Set SCL HI
i2c_SCL_L(); cWAIT_5_us; // Set SCL LO
d = d << 1;
} // end for
return i2c_check_ack();
} // end i2c_write_char()
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19. Do you see any opportunities for improvement?
Read char
int i2c_read_char(char *ch) {
auto char res,cnt;
for ( cnt=0,res=0; cnt<8; cnt++ ) {
i2c_SDA_H(); cWAIT_5_us;
if (i2c_wSCL_H()) return -1;
res <<= 1;
if (i2c_SDA()) res |= 0x01;
i2c_SCL_L(); cWAIT_5_us;
} // end for
*ch=res;
return 0;
} // end i2c_read_char
Do you see any opportunities for improvement?
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20. I2C on UI Project PCB
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21. PCF8574 I2C Expander
Can accommodate up to 8 devices on one I2C network
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22. PCF8574 I2C Expander
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23. Multi-Master I2C Network
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24. I2C Arbitration
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25. I2C Arbitration for 2 Masters
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26. I2C References Specification: Tutorials
Tutorials
Introduction to I2C (
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27. Quiz
List, and briefly describe, differences between RS232 and I2C communication in the Rabbit environment.
Do see anything wrong with this?
If (err=i2c_read_char(&data_byte)) { // Read data
i2c_stop_tx(); return 0xfc00 | err; } // Stretching error
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