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PCA9543 Datasheet PDF : 15 Pages
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Philips Semiconductors
2-channel I2C switch with interrupt logic and reset
Product data sheet
PCA9543
DEVICE ADDRESS
Following a START condition the bus master must output the
address of the slave it is accessing. The address of the PCA9543 is
shown in Figure 3. To conserve power, no internal pull-up resistors
are incorporated on the hardware selectable address pins and they
must be pulled HIGH or LOW.
1 1 1 0 0 A1 A0 R/W
FIXED
HARDWARE SELECTABLE
SW00893
Figure 3. Slave address
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.
CONTROL REGISTER
Following the successful acknowledgement of the slave address,
the bus master will send a byte to the PCA9543, which will be stored
in the control register. If multiple bytes are received by the
PCA9543, it will save the last byte received. This register can be
written and read via the I2C-bus.
INTERRUPT BITS CHANNEL SELECTION BITS
(READ ONLY)
(READ/WRITE)
7 65 4 3 21 0
7 6 INT1 INT0 X X B1 B0
CHANNEL 0
CHANNEL 1
INT0
INT1
SW01025
Figure 4. Control Register
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 PCA9543 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.
Table 1. Control Register; Write — Channel Selection/
Read — Channel Status
D7 D6 INT1 INT0 D3 D2 B1 B0 COMMAND
0
Channel 0
disabled
X
X
X
X
X
X
X
1
Channel 0
enabled
0
Channel 1
disabled
X
X
X
X
X
X
X
1
Channel 1
enabled
0 0 0 0 0 0 0 0 No channel
selected;
power-up/
reset default
state
NOTE: Channel 0 and 1 can be enabled at the same time. Care
should be taken not to exceed the maximum bus capacitance.
INTERRUPT HANDLING
The PCA9543 provides 2 interrupt inputs, one for each channel, and
one open drain interrupt output. When an interrupt is generated by any
device, it will be detected by the PCA9543 and the interrupt output
will be driven LOW. The channel need not be active for detection of
the interrupt. A bit is also set in the Control Register.
Bits 4 – 5 of the Control Register correspond to the INT0 and INT1
inputs of the PCA9543, respectively. Therefore, if an interrupt is
generated by any device connected to channel 1, the state of the
interrupt inputs is loaded into the control register when a read is
accomplished. Likewise, an interrupt on any device connected to
channel 0 would cause bit 4 of the control register to be set on the
read. The master can then address the PCA9543 and read the
contents of the Control Register to determine which channel
contains the device generating the interrupt. The master can then
reconfigure the PCA9543 to select this channel, and locate the
device generating the interrupt and clear it.
It should be noted that more than one device can be providing an
interrupt on a channel, so it is up to the master to ensure that all
devices on a channel are interrogated for an interrupt.
The interrupt inputs may be used as general purpose inputs if the
interrupt feature is not required.
If unused, interrupt input(s) must be connected to VDD through a
pull-up resistor.
Table 2. Control Register Read — Interrupt
7
6 INT1 INT0 3
2 B1 B0 COMMAND
0
No interrupt
on channel 0
X
X
X
X
X
X
X
1
Interrupt on
channel 0
0
No interrupt
on channel 1
X
X
X
X
X
X
X
1
Interrupt on
channel 1
NOTE: The two interrupts can be active at the same time.
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 PCA9543 will reset its registers and I2C state
machine and will deselect all channels. The RESET input must be
connected to VDD through a pull-up resistor.
POWER-ON RESET
When power is applied to VDD, an internal Power-On Reset holds
the PCA9543 in a reset state until VDD has reached VPOR. At this
point, the reset condition is released and the PCA9543 registers and
I2C state machine are initialized to their default states, all zeroes
causing all the channels to be deselected.
2004 Oct 01
4
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