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PCA9557 Datasheet(PDF) 6 Page - NXP Semiconductors

Part No. PCA9557
Description  8-bit I2C and SMBus I/0 port with reset
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Maker  PHILIPS [NXP Semiconductors]
Homepage  http://www.nxp.com
Logo PHILIPS - NXP Semiconductors

PCA9557 Datasheet(HTML) 6 Page - NXP Semiconductors

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Philips Semiconductors
Product data
PCA9557
8-bit I2C and SMBus I/0 port with reset
2001 Dec 12
6
DEVICE ADDRESS
Following a START condition the bus master must output the
address of the slave it is accessing. The address of the PCA9557 is
shown in Figure 6. To conserve power, no internal pullup resistors
are incorporated on the hardware selectable address pins and they
must be pulled HIGH or LOW.
00
1
1
A2
A1
A0
slave address
su01048
fixed
programmable
R/W
Figure 6. PCA9557 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 PCA9557, which will be stored
in the control register. This register can be written and read via the
I2C bus.
0
0
0
0
D1
D0
0
SW00953
0
Figure 7. Control Register
REGISTER DEFINITION
D1
D0
NAME
TYPE
FUNCTION
0
0
Register 0
Read
Input port register
0
1
Register 1
Read/Write
Output port register
1
0
Register 2
Read/Write
Polarity inversion
register
1
1
Register 3
Read/Write
Configuration
register
REGISTER DESCRIPTION
Register 0 – Input Port Register
I7
I6
I5
I4
I3
I2
I1
I0
This register is an read-only port. It reflects the incoming logic levels
of the pins, regardless of whether the pin is defined as an input or an
output by the Configuration Register. Writes to this register have no
effect.
Register 1 – Output Port Register
bit
O7
O6
O5
O4
O3
O2
O1
O0
default
0
0
0
0
0
0
0
0
This register reflects the outgoing logic levels of the pins defined as
outputs by the Configuration Register. Bit values in this register have
no effect on pins defined as inputs. In turn, reads from this register
reflect the value that is in the flip-flop controlling the output selection,
NOT the actual pin value.
Register 2 – Polarity Inversion Register
bit
N7
N6
N5
N4
N3
N2
N1
N0
default
1
1
1
1
0
0
0
0
This register enables polarity inversion of pins defined as inputs by
the Configuration Register. If a bit in this register is set (written
with ‘1’), the corresponding port pin’s polarity is inverted. If a bit in
this register is cleared (written with a ‘0’), the corresponding port
pin’s original polarity is retained.
Register 3 – Configuration Register
bit
C7
C6
C5
C4
C3
C2
C1
C0
default
1
1
1
1
1
1
1
1
This register configures the directions of the I/O pins. If a bit in this
register is set, the corresponding port pin is enabled as an input with
high impedance output driver. If a bit in this register is cleared, the
corresponding port pin is enabled as an output.
POWER-ON RESET
When power is applied to VDD, an internal power-on reset holds the
PCA9557 in a reset state until VDD has reached VPOR. At that point,
the reset condition is released and the PCA9557 registers and
I2C/SMBus state machine will initialize to their default states.
For a power reset cycle, VDD must be set to 0 V, then ramped back
to the operating voltage.
RESET INPUT
A reset can be accomplished by holding the RESET pin LOW for a
minimum of tW. The PCA9557 registers and SMBus/I2C state
machine will be held in their default state until the RESET input is
once again HIGH. This input typically requires a pull-up to VCC.


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