pca9539 datasheet

Table Of Contents

PCA9539

SCPS130G –AUGUST 2005–REVISED JUNE 2014

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8.3.2.3 Register Descriptions

The Input Port registers (registers 0 and 1) reflect the incoming logic levels of the pins, regardless of whether the

pin is defined as an input or an output by the Configuration register. It only acts on read operation. Writes to

these registers have no effect. The default value, X, is determined by the externally applied logic level.

Before a read operation, a write transmission is sent with the command byte to indicate to the I

C device that the

Input Port register will be accessed next.

Table 4. Registers 0 And 1 (Input Port Registers)

Bit I0.7 I0.6 I0.5 I0.4 I0.3 I0.2 I0.1 I0.0

Default X X X X X X X X

Bit I1.7 I1.6 I1.5 I1.4 I1.3 I1.2 I1.1 I1.0

Default X X X X X X X X

The Output Port registers (registers 2 and 3) show the outgoing logic levels of the pins defined as outputs by the

Configuration register. Bit values in this register have no effect on pins defined as inputs. In turn, reads from this

Table 5. Registers 2 And 3 (Output Port Registers)

Bit O0.7 O0.6 O0.5 O0.4 O0.3 O0.2 O0.1 O0.0

Default 1 1 1 1 1 1 1 1

Bit O1.7 O1.6 O1.5 O1.4 O1.3 O1.2 O1.1 O1.0

Default 1 1 1 1 1 1 1 1

The Polarity Inversion registers (registers 4 and 5) allow Polarity Inversion of pins defined as inputs by the

Configuration register. 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.

Table 6. Registers 4 And 5 (Polarity Inversion Registers)

Bit N0.7 N0.6 N0.5 N0.4 N0.3 N0.2 N0.1 N0.0

Default 0 0 0 0 0 0 0 0

Bit N1.7 N1.6 N1.5 N1.4 N1.3 N1.2 N1.1 N1.0

Default 0 0 0 0 0 0 0 0

The Configuration registers (registers 6 and 7) configure the directions of the I/O pins. If a bit in this register is

set to 1, the corresponding port pin is enabled as an input with a high-impedance output driver. If a bit in this

Table 7. Registers 6 And 7 (Configuration Registers)

Bit C0.7 C0.6 C0.5 C0.4 C0.3 C0.2 C0.1 C0.0

Default 1 1 1 1 1 1 1 1

Bit C1.7 C1.6 C1.5 C1.4 C1.3 C1.2 C1.1 C1.0

Default 1 1 1 1 1 1 1 1

8.3.2.4 Bus Transactions

Data is exchanged between the master and PCA9539 through write and read commands.

8.3.2.4.1 Writes

Data is transmitted to the PCA9539 by sending the device address and setting the least-significant bit to a logic 0

(see Figure 22 for device address). The command byte is sent after the address and determines which register

receives the data that follows the command byte.

Product Folder Links: PCA9539