PCA9541BSSLASH03 datasheet(27/43 Pages) NXP

27 / 43 page

PCA9541_5

Product data sheet

Rev. 05 — 1 October 2007

27 of 43

NXP Semiconductors

PCA9541

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 PCA9541 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 PCA9541/03 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 PCA9541/03 per card/device. Since each PCA9541/03 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 PCA9541/03 (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 PCA9541/03 is used.

Fig 20. Masters with shared resources application

002aab614

PCA9541

SLAVE A0

SLAVE A1

SLAVE A2

MASTER A

PCA9541

SLAVE B0

SLAVE B1

SLAVE B2

MASTER B

ASSEMBLY A

ASSEMBLY B

SDA/SCL

MAIN

MASTER

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