NXP Semiconductors
PCA9555
16-bit I
2
C-bus and SMBus I/O port with interrupt
6.2.2 Registers 0 and 1: Input port registers
This register is an input-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 Register 3. Writes to
this register have no effect.
The default value ‘X’ is determined by the externally applied logic level.
Table 5.
Bit
Symbol
Default
Table 6.
Bit
Symbol
Default
Input port 0 Register
7
I0.7
X
6
I0.6
X
5
I0.5
X
4
I0.4
X
3
I0.3
X
2
I0.2
X
1
I0.1
X
0
I0.0
X
Input port 1 register
7
I1.7
X
6
I1.6
X
5
I1.5
X
4
I1.4
X
3
I1.3
X
2
I1.2
X
1
I1.1
X
0
I1.0
X
6.2.3 Registers 2 and 3: Output port registers
This register is an output-only port. It reflects the outgoing logic levels of the pins defined
as outputs by Registers 6 and 7. 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.
Table 7.
Bit
Symbol
Default
Table 8.
Bit
Symbol
Default
Output port 0 register
7
O0.7
1
6
O0.6
1
5
O0.5
1
4
O0.4
1
3
O0.3
1
2
O0.2
1
1
O0.1
1
0
O0.0
1
Output port 1 register
7
O1.7
1
6
O1.6
1
5
O1.5
1
4
O1.4
1
3
O1.3
1
2
O1.2
1
1
O1.1
1
0
O1.0
1
6.2.4 Registers 4 and 5: Polarity Inversion registers
This register allows the user to invert the polarity of the Input port register data. If a bit in
this register is set (written with ‘1’), the Input port data polarity is inverted. If a bit in this
register is cleared (written with a ‘0’), the Input port data polarity is retained.
Table 9.
Bit
Symbol
Default
Table 10.
Bit
Symbol
Default
PCA9555_8
Polarity Inversion port 0 register
7
N0.7
0
6
N0.6
0
5
N0.5
0
4
N0.4
0
3
N0.3
0
2
N0.2
0
1
N0.1
0
0
N0.0
0
Polarity Inversion port 1 register
7
N1.7
0
6
N1.6
0
5
N1.5
0
4
N1.4
0
3
N1.3
0
2
N1.2
0
1
N1.1
0
0
N1.0
0
© NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 08 — 22 October 2009
7 of 34
PHILIPS [ NXP SEMICONDUCTORS ]
