PCA9556 Просмотр технического описания (PDF) - Philips Electronics

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PCA9556

Octal SMBus and I2C registered interface

Philips Electronics 

Philips Semiconductors

Octal SMBus and I2C registered interface

Product data

PCA9556

REGISTERS

Command Byte

Command

Protocol

0

Read byte

1

Read/write byte

2

Read/write byte

3

Read/write byte

Function

Input port register

Output port register

Polarity inversion register

Configuration register

The command byte is the first byte to follow the address byte during

a write transmission. It is used as a pointer to determine which of the

following registers will be written or read.

Register 0 — Input Port Register

I7

I6

I5

I4

I3

I2

I1

I0

This register is an read-only port. It reflects the incoming logic levels

of the pins, regardless of whether the pin is defined as an input or an

output by register 3. Writes to this register have no effect.

Register 1 — Output Port Register

bit O7 O6 O5 O4 O3 O2 O1 O0

default 0

0

0

0

0

0

0

0

This register reflects the outgoing logic levels of the pins defined as

outputs by register 3. Bit values in this register have no effect on

pins defined as inputs. In turn, reads from this register reflect the

value that is in the flip-flop controlling the output selection, NOT the

actual pin value.

Register 2 — Polarity Inversion Register

bit N7 N6 N5 N4 N3 N2 N1 N0

default 1

1

1

1

0

0

0

0

This register enables polarity inversion of pins defined as inputs by

register 3. If a bit in this register is set (written with ‘1’), the

corresponding port pin’s polarity is inverted. If a bit in this register is

cleared (written with a ‘0’), the corresponding port pin’s original

polarity is retained.

Register 3 — Configuration Register

bit C7 C6 C5 C4 C3 C2 C1 C0

default 1

1

1

1

1

1

1

1

This register configures the directions of the I/O pins. If a bit in this

register is set, the corresponding port pin is enabled as an input with

high impedance output driver. If a bit in this register is cleared, the

corresponding port pin is enabled as an output.

RESET

Power-on Reset

When power is applied to VDD, an internal power-on reset holds the

PCA9556 in a reset state until VDD has reached VPOR. At that point,

the reset condition is released and the PCA9556 registers and

SMBus state machine will initialize to their default states.

External Reset

A reset can be accomplished by holding the RESET pin low for a

minimum of TW. The PCA9556 registers and SMBus/I2C state

machine will be held in their default state until the RESET input is

once again high. This input typically requires a pull-up to 3.3 V VCC.

2002 Mar 28

4

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