PCA9556 Philips Semiconductors, PCA9556 Datasheet - Page 3

• Manufacturer Part Number: PCA9556
• Description: Octal SMBus Registered Interface
• Manufacturer: Philips Semiconductors

Philips Semiconductors
BLOCK DIAGRAM
REGISTERS
Command Byte
The command byte is the first byte to follow the address byte during
a write transmission. It is used as a pointer to determine which of the
following registers will be written or read.
Register 0 – Input Port Register
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.
Register 1 – Output Port Register
This register is an output-only port. It reflects the outgoing logic
levels of the pins defined as outputs by register 3. 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.
1998 Dec 18
default
Command
Octal SMBus Registered Interface
bit
I7
0
1
2
3
O7
I6
0
RESET
Read/write byte
Read/write byte
Read/write byte
O6
SDA
0
SCL
V
V
Read byte
I5
SS
Protocol
A0
A1
A2
DD
O5
0
I4
O4
0
FILTER
INPUT
I3
Function
Polarity inversion register
I/O configuration register
Input port register
Output port register
O3
0
POWER-
RESET
ON
I2
O2
0
I1
O1
0
Figure 2. Block diagram
I0
O0
0
CONTROL
SMBUS
3
Register 2 – Polarity Inversion Register
This register enables polarity inversion of pins defined as inputs by
register 3. 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 – Input/Output Configuration Register
This register configures the directions of the I/O pins. If a bit in this
register is set (written with ‘1’), the corresponding port pin is enabled
as an input with high impedance output driver. If a bit in this register
is cleared (written with ‘0’), the corresponding port pin is enabled as
an output.
RESET
Power-on Reset
When power is applied to V
PCA9556 in a reset state until V
the reset condition is released and the PCA9556 registers and
SMBus state machine will initialize to their default states.
External Reset
A reset can be accomplished by holding the RESET pin low for a
minimum of T
will be held in their default state until the RESET input is once again
high. This input contains an internal pull-up, therefore, it may be left
open if not used.
default
default
bit
bit
WRITE pulse
READ pulse
NOTE: ALL I/Os ARE SET TO INPUTS AT RESET
8-BIT
C7
N7
1
1
W
. The PCA9556 registers and SMBus state machine
C6
N6
1
1
PORTS
INPUT/
OUT-
PUT
C5
N5
1
1
DD
, an internal power-on reset holds the
DD
C4
N4
1
1
has reached V
su01046
C3
N3
I/O0
I/O1
I/O2
I/O3
I/O4
I/O5
I/O6
I/O7
1
0
Product specification
C2
N2
PCA9556
1
0
POR
. At that point,
C1
N1
1
0
N0
C0
0
1