App Clip
9/28/04
8:58 AM
Page 1
PCF8574 and PCF8574A I/O Expanders
Texas Instruments’ (TI) PCF8574 and PCF8574A are two-wire I2C-bus to
8-bit parallel bus I/O expanders from TI’s I2C logic portfolio. They are
designed to provide a simple and cost-effective method to monitor and
control several peripheral signals. The difference between the PCF8574
and PCF8574A is the I2C address:
•
PCF8574 has addresses ranging from 0x20 to 0x27 (up to
eight PCF8574 devices may be used on the same I2C bus).
SDA
MSB
SCL
1
Start
Condition
2
3-6
•
The PCF8574 and PCF8574A have addresses ranging from 0x38 to
0x3F (up to eight PCF8574A devices may be used on the same I2C
bus).
•
A total of 16 PCF8574 and PCF8574A devices may be used
on the same I2C bus.
The PCF8574 and PCF8574A use the serial clock (SCL) and serial data
(SDA) I2C lines to communicate with the bus controller.
—
LSB
R/W
RX-ACK
MSB
7
8
9
1
Address Transfer
From Master to Slave
Data
Direction Bit
2
3-7
LSB
RX-ACK
8
9
Data Transfer From Master to Slave (Write)
or Slave to Master (Read)
Stop
Condition
PCF8574/A Functional Block Diagram*
Key Features
•
Pin-to-pin compatible and functionally
equivalent with Philips PCF8574 and
PCF8574A (PDIP, SOIC and TSSOP)
•
In addition, TI has package offerings that
are smaller than Philips package options:
– 20-pin TVSOP (23% smaller than
20-pin TSSOP)
– 20-pin QFN package (62% smaller than
20-pin TSSOP); industry’s smallest
PCF8574 and PCF8574A package
•
Two-wire I2C-bus to 8-bit bidirectional
parallel-bus expander
•
Operating supply voltage from 2.5-V to
6-V VCC
•
Low standby current consumption
of 10 mA maximum (FSCL =OHZ)
•
Open-drain interrupt output to signal a
change on an I/O pin
•
Latched outputs with high-current
drive capability for driving LEDs
•
•
R
Addressed by three hardware-address pins
16-Pin SOIC
(Philips Cross)
Top applications:
– Fan control
– LED driver
– System monitoring
– Temperature sensor monitoring
– Push button monitoring
– 8-bit bidirectional expansion
E L I A B L E.
L
5.0 mm
10.3 mm
O G I C.
10.3 mm
6.4 mm
1.27–mm pitch
0.4–mm pitch
6.5 mm
4.5 mm
20-Pin TSSOP
(Philips Cross)
6.5 mm
0.65–mm pitch
I
20-Pin TVSOP
20-Pin QFN
3.5 mm
0.5–mm pitch
TM
N N O V A T I O N.
App Clip
9/28/04
8:58 AM
Page 2
Applications With Multiple PCF8574 and PCF8574A Devices
20 (hexadecimal)
21 (hexadecimal)
22 (hexadecimal)
23 (hexadecimal)
24 (hexadecimal)
25 (hexadecimal)
26 (hexadecimal)
27 (hexadecimal)
PCF8574A I2C-Bus
Slave Address
INT
38 (hexadecimal)
39 (hexadecimal)
3A (hexadecimal)
3B (hexadecimal)
3C (hexadecimal)
3D (hexadecimal)
3E (hexadecimal)
3F (hexadecimal)
PCF8574
address = 0100 000
VCC
VCC
SDA P0
SCL P1
INT P2
P3
P4
A0
P6
A1
P7
P8
A2
VCC
SDA P0
SCL P1
INT P2
P3
P4
A0
P6
A1
P7
P8
A2
A2 = L
A1 = L
A0 = H
PCF8574
PCF8574A
address = 0100 001 address = 0111 000
13
A2 1
A1 2
A0 3
SCL 14
SDA 15
SCL 14
SDA 15
VCC
13
A2 1
A1 2
A0 3
SCL 14
SDA 15
P0
P1
P2
P3
P4
P5
P6
P7
P65
P66
P67
P68
P69
P70
P71
P72
P0
P1
P2
P3
P4
P5
P6
P7
P73
P74
P75
P78
P77
P78
P79
P80
P0
P1
P2
P3
P4
P5
P6
P7
P121
P122
P123
P124
P125
P126
P127
P128
VDD
4
5
6
7
9
10
11
8 12
P0
P1
P2
P3
P4
P5
P6
P7
INT
P9
P10
P11
P12
P13
P14
P15
P16
13
A2 1
A1 2
A0 3
A2 = L
A1 = L
A0 = H
SCL 14
SDA 15
4
5
6
7
9
10
11
8 12
U10
VDD
A2 = H
A1 = H
A0 = H
4
5
6
7
9
10
11
8 12
U9
U2
SDA P0
SCL P1
INT P2
P3
P4
A0
P6
A1
P7
P8
A2
VCC
A2 = L
A1 = L
A0 = L
VDD
INT
VCC
SDA P0
SCL P1
INT P2
P3
P4
A0
P6
A1
P7
P8
A2
13
A2 1
A1 2
A0 3
U1
VCC
Core
Processor
INT
P1
P2
P3
P4
P5
P6
P7
P8
PCF8574A
SCL 14
SDA 15
P0
P1
P2
P3
P4
P5
P6
P7
PCF8574A
L
H
L
H
L
H
L
H
SCL
4
5
6
7
9
10
11
8 12
VDD
4
5
6
7
9
10
11
8 12
P0
P1
P2
P3
P4
P5
P6
P7
INT
P57
P58
P59
P60
P61
P62
P63
P64
A2 = H
A1 = H
A0 = H
4.7 k Ω
4.7 k Ω
13
A2 1
A1 2
A0 3
SCL 14
SDA 15
U8
4
5
6
7
9
10
11
8 12
PCF8574A
L
L
H
H
L
L
H
H
A2 = L
A1 = L
A0 = L
SDA
13
A2 1
A1 2
A0 3
PCF8574
L
L
L
L
H
H
H
H
PCF8574 I2C-Bus
Slave Address
INPUTS
A1
A0
INT
INT
VDD
PCF8574
A2
VDD
4.7 k Ω
PCF8574
The expanders can be configured to have a unique 7-bit address. The first
four bits of the PCF8574’s 7-bit address are 0100, and those for the
PCF8574A are 0111. The lower three bits are the settings on the device
pins A2, A1, and A0. This ability to set unique addresses for the expanders
makes it possible to have up to eight PCF8574 and eight PCF8574A
devices on the same I2C bus.
PCF8574 and PCF8574A I2C-Bus Slave Address Map
U16
PCF8574A
address = 0111 001
*All pin numbers shown are for 16-pin SOIC and PDIP packages. See datasheets for 20-pin
package options.
Bi-Directional I/O Expander Applications
VCC
SDA
Core
Processor
SCL
INT
A0
A1
A2
—
The TI PCF8574 and PCF8574A also have an interrupt line (INT) that can
be connected to the interrupt logic of the microprocessor. By sending an
interrupt signal on this line, the remote I/O informs the microprocessor
that there is incoming data or a change of data on its ports without
having to communicate via the I2C communication bus.
P0
P1
P2
P3
P4
P5
P6
P7
Temperature Sensor
Battery Status
Control for Latch
Control for Switch
Control for Audio
Control for Camera
Control for MP3
VCC
High Current-Drive Load Applications
VCC
VCC
Core
Processor
SDA
SCL
INT
For More Information: www.ti.com/i2c
A0
A1
A2
PCF8574
The PCF8574 and PCF8574A have a maximum sinking current of 25 mA.
In applications requiring additional drive, two port pins may be
connected together to sink up to 50-mA current.
VCC
VCC
PCF8574
In the I/O expander application shown here, the PCF8574 or PCF8574A is
used with P0 and P1 as inputs and P2 to P7 as outputs. When used in this
configuration, during a write, the inputs (P0 and P1) must be written as
high so the external devices fully control the input ports. The desired high
or low logic levels may be written to the I/Os used as outputs (P2 to P7).
During a read, the logic levels of the external devices driving the input ports
(P0 and P1) and the previous written logic levels to the output ports
(P2 to P7) will be read.
P0
P1
P2
P3
P4
P5
P6
P7
Load
Product Folders: www.ti.com/sc/device/PCF8574 • www.ti.com/sc/device/PCF8574A
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