PCA9544A All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 5 — 23 April 2014 6 of 31
NXP Semiconductors
PCA9544A
4-channel I
2
C-bus multiplexer with interrupt logic
6. Functional description
Refer to Figure 1 “Block diagram”.
6.1 Device addressing
Following a START condition the bus master must output the address of the slave it is
accessing. The address of the PCA9544A is shown in Figure 5
. To conserve power, no
internal pull-up resistors are incorporated on the hardware selectable address pins and
they must be pulled HIGH or LOW.
The last bit of the slave address defines the operation to be performed. When set to
logic 1 a read is selected, while a logic 0 selects a write operation.
6.2 Control register
Following the successful acknowledgement of the slave address, the bus master sends a
byte to the PCA9544A which is stored in the Control register. If the PCA9544A receives
multiple bytes, it saves the last byte received. This register can be written and read via the
I
2
C-bus.
6.2.1 Control register definition
A SCx/SDx downstream pair, or channel, is selected by the contents of the control
register. This register is written after the PCA9544A has been addressed. The 3 LSBs of
the control byte are used to determine which channel is to be selected. When a channel is
selected, it will become active after a STOP condition has been placed on the I
2
C-bus.
This ensures that all SCx/SDx lines are in a HIGH state when the channel is made active,
so that no false conditions are generated at the time of connection.
Fig 5. Slave address
002aab189
1 1 1 0 A2 A1 A0 R/W
fixed hardware
selectable
Fig 6. Control register
002aae297
INT3 INT2 INT1 INT0 X B2 B1 B0
interrupt bits
(read only)
channel selection bits
(read/write)
76543210bit
enable bit
