PCA9541APWSLASH01 datasheet(26/41 Pages) NXP

26 / 41 page

PCA9541A_3

Product data sheet

Rev. 03 — 16 July 2009

26 of 41

NXP Semiconductors

PCA9541A

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

10.3 Masters with shared resources

Some masters may not be multi-master capable or some masters may not work well

together and continually lock up the bus. The PCA9541A can be used to separate the

masters, as shown in Figure 20, but still allow shared access to slave devices, such as

Field Replaceable Unit (FRU) EEPROMs or temperature sensors.

10.4 Gatekeeper multiplexer

The PCA9541A/03 can act as a gatekeeper multiplexer in applications where there are

multiple I2C-bus devices with the same ﬁxed address (for example, EEPROMs with

address of ‘Z’ as shown in Figure 21) connected in a multipoint arrangement to the same

I2C-bus. Up to 16 hot swappable cards/devices can be multiplexed to the same bus

master by using one PCA9541A/03 per card/device. Since each PCA9541A/03 has its

own unique address (for example, ‘A’, ‘B’, ‘C’, and so on), the EEPROMs can be

connected to the master, one at a time, by connecting one PCA9541A/03 (Master 0

position) while keeping the rest of the cards/devices isolated (off position).

The alternative, shown with dashed lines, is to use a PCA9548 1-to-8 channel switch on

the master card and run 8 I2C-bus devices, one to each EEPROM card, to multiplex the

master to each card. The number of card pins used is the same in either case, but there

are 7 less pairs of SDA/SCL traces on the printed-circuit board if the PCA9541A/03 is

used.

Fig 20. Masters with shared resources application

002aae664

PCA9541A

SLAVE A0

SLAVE A1

SLAVE A2

MASTER A

PCA9541A

SLAVE B0

SLAVE B1

SLAVE B2

MASTER B

ASSEMBLY A

ASSEMBLY B

SDA/SCL

MAIN

MASTER

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