PCA9541APWSLASH01 datasheet(12/45 Pages) NXP

12 / 45 page

PCA9541A

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Product data sheet

Rev. 5 — 24 April 2014

12 of 45

NXP Semiconductors

PCA9541A

2-to-1 I2C-bus master selector with interrupt logic and reset

[1]

BUSON and NBUSON is an exclusive-OR type function where:

Equal values (00b or 11b) means that the connection between the upstream and the downstream channels

is off.

Different values (01b or 10b) means that the connection between the upstream and the downstream

channels is on.

Switch to the new channel is done when the master initiating the switch request sends a

STOP command to the PCA9541A.

If either master wants to change the connection of the downstream channel, it must write

to its Control Register (Reg#01), and then send a STOP command because an update

of the connection to the downstream according to the values in the two internal Control

Registers happens only on a STOP command. Writing to one control register followed by

a STOP condition on the other master's channel does not cause an update to the

downstream connection.

When both masters request a switch to their own channel at the same time, the master

who last wrote to its Control Register before the PCA9541A receives a STOP command

wins the switching sequence. There is no arbitration performed.

The Auto Increment feature (AI = 1) allows programming the PCA9541A in 4 bytes:

Start

111A3A2A1A0 + 0

PCA9541 Address + Write

00010000

Select Reg#00 with AI = 1

Data Reg#00

Interrupt Enable Register data

Data Reg#01

Control Register data

Stop

Table 12 describes which command must be written to the Control Register when a

master device wants to take control of the I2C-bus. Byte written to the Control Register is

a function of the current I2C-bus control status performed after an initial reading of the

Control Register.

Table 10.

BUSON and NBUSON truth table

NBUSON[1] BUSON[1]

Slave channel

off

Table 11.

Default Control Register values

Type version

Master

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

NTESTON

TESTON

not used

BUSINIT

NBUSON

BUSON

NMYBUS

MYBUS

PCA9541A/01 MST_0

0000

010

MST_1

0000

101

PCA9541A/03 MST_0

0000

000

MST_1

0000

001

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