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How the I2C Bus Works - EEWeb

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Supply<br />

SDA<br />

SCL<br />

Sub address<br />

decoder<br />

Quasi Output I 2 C I/O Expanders<br />

General Purpose I/O<br />

POR<br />

I 2 C-bus<br />

interface<br />

Latches<br />

Interrupt<br />

巨<br />

Input/ output stages<br />

alternative analog input<br />

configurations<br />

# of Outputs Interrupt<br />

KEY POINTS<br />

- Transfers keyboard, ACPI Power switch, keypad,<br />

switch or o<strong>the</strong>r inputs to microcontroller via I 2 C bus<br />

- Expand microcontroller via I 2 C bus where I/O can<br />

be located near <strong>the</strong> source or on various cards<br />

- Use outputs to drive LEDs, sensors, fans, enable<br />

and o<strong>the</strong>r input pins, relays and timers<br />

- Quasi outputs can be used as Input or Output<br />

without <strong>the</strong> use of a configuration register<br />

- The PCA9501 has 6 address pins, allowing up to 64<br />

devices to share <strong>the</strong> same I 2 C <strong>Bus</strong>.<br />

- Application Note, AN469 GPIO Selection, discusses<br />

pros and cons of GPIOs<br />

2Kbit<br />

EEPROM<br />

Interrupt and<br />

2Kbit EEPROM<br />

Quasi Output (20-25 ma sink and 100 uA source)<br />

8 PCF8574/74A PCA9500/58 PCA9501<br />

16 PCF8575/75C - -<br />

Semiconductors 35

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