I2C

2010/05/13 by Sean Chen

Agenda

• What’s I2C?• I2C Protocol• Other I2C Bus• I2C components

– NXP UM1024

• Data transfer • How to R/W I2C?• Iboot• References

What’s I2C?

• Definition– I²C (Inter-Integrated Circuit) is a multi-master serial

single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, or cellphone.

• Internal Bus– (400 kbit/s Fast mode, 1 Mbit/s Fast mode plus or Fm

+, and 3.4 Mbit/s High Speed mode);

I2C Protocol 1/2• protocol

– Serial Data Line(SDA) – Serial Clock (SCL)– RD

• Pull up resistors– Switch on/off

• Speed– per-byte ACK/NACK bits.

• keywords– Master– Slaver

I2C Protocol 2/2

• Timing diagram

Data transfer is initiated with the START bit (S) when SDA is pulled low while SCL stays high. Then, SDA sets the transferred bit while SCL is low (blue) and the data is sampled (received) when SCL rises (green). When the transfer is complete, a STOP bit (P) is sent by releasing the data line to allow it to be pulled up while SCL is constantly high.

Other I2C Bus

• Other I2C Bus– CBUS compatibility– SMBus - System Management Bus

• is a single-ended simple two-wire bus for the purpose of lightweight communication. Most commonly it is found in computer motherboards for communication with the power source for ON/OFF instructions.

– PMBus - Power Management Bus• is a variant of the System Management Bus (SMBus) which i

s targeted at digital management of power supplies. Like SMBus, it is a relatively slow speed two wire communications protocol based on I²C.

– Intelligent Platform Management Interface (IPMI)

NXP UM1024

• I2C components

Data transfer

• Data transfer– Master – Slaver Selection (Slave Address)

• Mode (R/W)

– Data transfer• N bytes + ack

How to R/W I2C?

• i2c_rx– Config

• Address• registers• is_write

– Flase

• bufferLen– Transfer data length unit(bytes)

– Do• I2c_readwrite

– FSM» Case : Start ()? NT=I2CSendRegister: NT=I2CSetup;» Case : I2CSendRegister ..» ….» ST=NT;

Iboot-> I2C.h

• iboot– I2CState

• I2CStart• I2CTx• I2CRx• I2CSendRegister• ….

– I2CInfo• I2CState• uint32_t address;• uint32_t frequency;• uint8_t* buffer;

– Gpio Interface

Iboot-> I2C.c

• iBoot->I2C / 2 I2C Bus– i2c_setup

• clock_gate_switch(I2C0_CLOCKGATE, ON);• init_i2c(&I2C[0], FrequencyBasePeripheral);

– settings» Frequency;» divisorRequired;» Prescaler;» gpio_custom_io;

• Methods– I2CError i2c_rx(

int bus, int iicaddr, const uint8_t* registers, int num_regs, void* buffer, int len);

– I2CError i2c_tx(int bus, int iicaddr, void* buffer, int len);

References

• I2C protocol 原理及應用 – http://jyhshin3.blogspot.com/2009/04/ic-inter-integrate

d-circuit.html

• NXP UM10204.pdf– http://www.nxp.com/documents/user_manual/UM102

04.pdf

• WiKi I2C– http://en.wikipedia.org/wiki/I%C2%B2C