PCA9548APW datasheet(7/25 Pages) PHILIPS

7 / 25 page

9397 750 13297

Product data sheet

Rev. 01 — 15 April 2005

7 of 25

Philips Semiconductors

PCA9548A

8-channel I2C switch with reset

7.2.1 Control register deﬁnition

One or several SCx/SDx downstream pair, or channel, is selected by the contents of the

control register. This register is written after the PCA9548A has been addressed. The

2 LSBs of the control byte are used to determine which channel is to be selected. When a

channel is selected, the channel will become active after a STOP condition has been

placed on the I2C-bus. This ensures that all SCx/SDx lines will be in a HIGH state when

the channel is made active, so that no false conditions are generated at the time of

connection.

Remark: Multiple channels can be enabled at the same time. Example: B7 = 0, B6 = 1,

B5 = 0, B4 = 0, B3 = 1, B2 = 1, B1 = 0, B0 = 0, means that channels 7, 5, 4, 1 and 0 are

disabled and channels 6, 3, and 2 are enabled. Care should be taken not to exceed the

maximum bus capacitance. Default condition is all zeroes.

7.3 RESET input

The RESET input is an active LOW signal which may be used to recover from a bus fault

condition. By asserting this signal LOW for a minimum of tWL, the PCA9548A will reset its

be connected to VDD through a pull-up resistor.

7.4 Power-on reset

When power is applied to VDD, an internal Power-On Reset (POR) holds the PCA9548A in

a reset condition until VDD has reached VPOR. At this point, the reset condition is released

and the PCA9548A register and I2C-bus state machine are initialized to their default

states—all zeroes—causing all the channels to be deselected. Thereafter, VDD must be

lowered below 0.2 V to reset the device.

Table 4:

Control register: Write—channel selection; Read—channel status

Command

XXXXXXX

channel 0 disabled

channel 0 enabled

XXXXXX

channel 1 disabled

channel 1 enabled

XXXXX

channel 2 disabled

channel 2 enabled

XXXX

XXX

channel 3 disabled

channel 3 enabled

XXX

XXXX

channel 4 disabled

channel 4 enabled

XXXXX

channel 5 disabled

channel 5 enabled

XXXXXX

channel 6 disabled

channel 6 enabled

XXXXXXX

channel 7 disabled

channel 7 enabled

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