PCA9544 Philips Semiconductors, PCA9544 Datasheet - Page 4

• Manufacturer Part Number: PCA9544
• Description: 4-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
PCA9544 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
X
X
7
4-channel I
6
X
X
X
X
X
X
X
X
X
X
CONTROL BYTE
5
INT3
7
2
INT2 INT1 INT0
Interrupt bits
(read only)
C bus. This ensures that all SCx/SDx lines will
X
X
X
X
X
4
6
2
C multiplexer and interrupt controller
5
X
X
X
X
X
3
4
2
0
1
1
1
1
3
X
Channel select bits
1
X
0
0
1
1
B2
2
(read/write)
1
B1
0
X
0
1
0
1
B0
0
0 (SC0/SD0)
1 (SC1/SD1)
2 (SC2/SD2)
3 (SC3/SD3)
SELECTED
CHANNEL
none
SW00386
4
INTERRUPT HANDLING
The PCA9544 provides 4 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 PCA9544 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 – 7 of the
control byte correspond to channels 0 – 3 of the PCA9544,
respectively. Therefore, if an interrupt is generated by any device
connected to channel 2, then bit 6 will be set in the control register.
Likewise, an interrupt on any device connected to channel 3 would
cause bit 7 of the control register to be set. The master can then
address the PCA 9544 and read the contents of the control byte to
determine which channel contains the device generating the interrupt.
The master can then reconfigure the PCA9544 to select this
channel, and locate the device generating the interrupt and clear it.
The interrupt clears when the device originating the interrupt clears.
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
0
1
6
0
0
1
0
5
0
1
0
0
4
1
0
0
0
3
X
X
X
X
X
X
X
X
2
X
X
X
X
1
0
X
X
X
X
Product specification
PCA9544
INTERRUPTING
0 (SC0/SD0)
1 (SC1/SD1)
2 (SC2/SD2)
3 (SC3/SD3)
CHANNEL