NXP Semiconductors

PCA9537

4-bit I2C-bus and SMBus low power I/O port with interrupt and reset

6.2.1 Command byte

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 registers will be written or read.

Command

Protocol

Function

0

read byte

Input Port register

1

read/write byte

Output Port register

2

read/write byte

Polarity Inversion register

3

read/write byte

Configuration register

Table 4. Command byte

6.2.2 Register 0 - Input Port register

This register is a 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.

The default value ‘X’ is determined by the externally applied logic level.

Legend: * default value.

Bit

Symbol

Access

Value

Description

7

I7

read only

1*

6

I6

read only

1*

5

I5

read only

1*

4

I4

read only

1*

not used

3

I3

read only

X*

2

I2

read only

X*

1

I1

read only

X*

0

I0

read only

X*

value ‘X’ is determined by externally applied logic

level

Table 5. Register 0 - Input Port register bit description

6.2.3 Register 1 - Output Port register

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. Reads from this

register return the value that is in the flip-flop controlling the output selection,

not the

actual pin value.

Legend: * default value.

Bit

Symbol

Access

Value

Description

7

O7

R

1*

6

O6

R

1*

5

O5

R

1*

4

O4

R

1*

not used

Table 6. Register 1 - Output Port register bit description

PCA9537

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Product data sheet

Rev. 7 — 8 September 2021

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