PCA9548 Просмотр технического описания (PDF) - Philips Electronics
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PCA9548 Datasheet PDF : 16 Pages
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Philips Semiconductors
8-channel I2C switch with reset
Product data sheet
PCA9548
DEVICE ADDRESSING
Following a START condition the bus master must output the
address of the slave it is accessing. The address of the PCA9548 is
shown in Figure 3. To conserve power, no internal pullup resistors
are incorporated on the hardware selectable address pins and they
must be pulled HIGH or LOW.
1 1 1 0 A2 A1 A0 R/W
FIXED
HARDWARE SELECTABLE
SW00915
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 PCA9548, which will be stored
in the control register. If multiple bytes are received by the
PCA9548, it will save the last byte received. This register can be
written and read via the I2C-bus.
CHANNEL SELECTION BITS
(READ/WRITE)
76 5 43 21 0
B7 B6 B5 B4 B3 B2 B1 B0
CHANNEL 0
CHANNEL 1
CHANNEL 2
CHANNEL 3
CHANNEL 4
CHANNEL 5
CHANNEL 6
CHANNEL 7
SW00932
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 PCA9548 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
B7 B6 B5 B4 B3 B2 B1 B0 COMMAND
0
Channel 0
disabled
XXXXXXX
1
Channel 0
enabled
0
Channel 1
disabled
XXXXXX
X
1
Channel 1
enabled
0
Channel 2
disabled
XXXXX
XX
1
Channel 2
enabled
0
Channel 3
disabled
XXXX
XXX
1
Channel 3
enabled
0
Channel 4
disabled
XXX
XXXX
1
Channel 4
enabled
0
Channel 5
disabled
XX
XXXXX
1
Channel 5
enabled
0
Channel 6
disabled
X
XXXXXX
1
Channel 6
enabled
0
Channel 7
disabled
XXXXXXX
1
Channel 7
enabled
No channel
0
0
0
0
0
0
0
0
selected;
power-up/reset
default state
NOTE: Several channels can be enabled at the same time.
Ex: 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.
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 PCA9548 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 PCA9548 in a reset state until VDD has reached VPOR. At this
point, the reset condition is released and the PCA9548 registers and
I2C state machine are initialized to their default states, all zeroes
causing all the channels to be deselected.
2004 Sep 30
5
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