PCA9542 Philips Semiconductors, PCA9542 Datasheet - Page 4

• Manufacturer Part Number: PCA9542
• Description: 2-channel I2C multiplexer and interrupt controller
• Manufacturer: Philips Semiconductors

Philips Semiconductors
CHANNEL SELECTION
A SC0x/SD0x downstream pair, or channel, is selected by the
contents of the control register. This register is written after the
PCA9542 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, the channel will become active after a stop condition has
been placed on the I
be in a HIGH state when the channel is made active, so that no
false conditions are generated at the time of connection.
CONTROL REGISTER
POWER-ON RESET
During power-up, the control register defaults to all zeroes causing
all the channels to be deselected.
1999 Oct 07
X
X
X
7
2-channel I
6
X
X
X
X
X
X
CONTROL BYTE
5
X
7
2
C bus. This ensures that all SCx/SDx lines will
X
X
X
4
X
6
2
Interrupt bits
C multiplexer and interrupt controller
(read only)
INT1 INT0
5
X
X
X
3
4
2
0
1
1
3
X
1
X
0
0
B2
Channel select bits
2
(read/write)
1
B1
0
X
0
1
B0
0
0 (SC0/SD0)
1 (SC1/SD1)
SELECTED
CHANNEL
none
SW00477
4
INTERRUPT HANDLING
The PCA9542 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 PCA9542 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 byte.
Bits 4 – 5 of the control byte correspond to channels 0 – 1 of the
PCA9542, respectively. Therefore, if an interrupt is generated by any
device connected to channel 1, then bit 5 will be set in the control
register. Likewise, an interrupt on any device connected to channel 0
would cause bit 4 of the control register to be set. The master can
then address the PCA9542 and read the contents of the control byte
to determine which channel contains the device generating the
interrupt. The master can then reconfigure the PCA9542 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.
7
0
0
6
0
0
5
0
1
4
1
0
3
X
X
X
X
2
X
X
1
0
X
X
Product specification
PCA9542
INTERRUPTING
0 (SC0/SD0)
1 (SC1/SD1)
CHANNEL