1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

FEATURES

Operating supply voltage 2.5 to 6 V

Low standby current consumption of 10

A maximum

C to parallel port expander

Open-drain interrupt output

8-bit remote I/O port for the I

C-bus

Compatible with most microcontrollers

Latched outputs with high current drive capability for
directly driving LEDs

Address by 3 hardware address pins for use of up to
8 devices (up to 16 with PCF8574A)

DIP16, or space-saving SO16 or SSOP20 packages.

GENERAL DESCRIPTION

The PCF8574 is a silicon CMOS circuit. It provides general
purpose remote I/O expansion for most microcontroller
families via the two-line bidirectional bus (I

C).

The device consists of an 8-bit quasi-bidirectional port and
an I

C-bus interface. The PCF8574 has a low current

consumption and includes latched outputs with high
current drive capability for directly driving LEDs. It also
possesses an interrupt line (INT) which can be connected
to the interrupt logic of the microcontroller. By sending an
interrupt signal on this line, the remote I/O can inform the
microcontroller if there is incoming data on its ports without
having to communicate via the I

C-bus. This means that

the PCF8574 can remain a simple slave device.

The PCF8574 and PCF8574A versions differ only in their
slave address as shown in Fig.9.

ORDERING INFORMATION

TYPE NUMBER

PACKAGE

NAME

DESCRIPTION

VERSION

PCF8574P;
PCF8574AP

DIP16

plastic dual in-line package; 16 leads (300 mil)

SOT38-1

PCF8574T;
PCF8574AT

SO16

plastic small outline package; 16 leads; body width 7.5 mm

SOT162-1

PCF8574TS

SSOP20

plastic shrink small outline package; 20 leads; body width 4.4 mm

SOT266-1

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

PINNING

SYMBOL

PIN

DESCRIPTION

DIP16; SO16

SSOP20

address input 0

address input 1

address input 2

quasi-bidirectional I/O 0

quasi-bidirectional I/O 1

quasi-bidirectional I/O 2

quasi-bidirectional I/O 3

supply ground

quasi-bidirectional I/O 4

quasi-bidirectional I/O 5

quasi-bidirectional I/O 6

quasi-bidirectional I/O 7

INT

interrupt output (active LOW)

SCL

serial clock line

SDA

serial data line

supply voltage

n.c.

not connected

n.c.

not connected

n.c.

not connected

n.c.

not connected

handbook, halfpage

INT

SDA

VSS

SCL

VDD

PCF8574

PCF8574A

MBD979

Fig.2 Pin configuration (DIP16; SO16).

handbook, halfpage

INT

SCL

n.c.

SDA

VDD

n.c.

VSS

n.c.

PCF8574TS

MBD978

Fig.3 Pin configuration (SSOP20).

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

CHARACTERISTICS OF THE I

C-BUS

The I

C-bus is for 2-way, 2-line communication between

different ICs or modules. The two lines are a serial data
line (SDA) and a serial clock line (SCL). Both lines must be
connected to a positive supply via a pull-up resistor when
connected to the output stages of a device. Data transfer
may be initiated only when the bus is not busy.

6.1

Bit transfer

One data bit is transferred during each clock pulse. The
data on the SDA line must remain stable during the HIGH
period of the clock pulse as changes in the data line at this
time will be interpreted as control signals (see Fig.4).

6.2

Start and stop conditions

Both data and clock lines remain HIGH when the bus is not
busy. A HIGH-to-LOW transition of the data line, while the
clock is HIGH is defined as the start condition (S).
A LOW-to-HIGH transition of the data line while the clock
is HIGH is defined as the stop condition (P) (see Fig.5).

6.3

System configuration

A device generating a message is a `transmitter', a device
receiving is the `receiver'. The device that controls the
message is the `master' and the devices which are
controlled by the master are the `slaves' (see Fig.6).

Fig.4 Bit transfer.

MBC621

data line

stable;

data valid

change

of data

allowed

SDA

SCL

Fig.5 Definition of start and stop conditions.

MBC622

SDA

SCL

STOP condition

SDA

SCL

START condition

Fig.6 System configuration.

MBA605

MASTER

TRANSMITTER /

RECEIVER

SLAVE

RECEIVER

SLAVE

TRANSMITTER /

RECEIVER

MASTER

TRANSMITTER

MASTER

TRANSMITTER /

RECEIVER

SDA

SCL

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

6.4

Acknowledge

The number of data bytes transferred between the start
and the stop conditions from transmitter to receiver is not
limited. Each byte of eight bits is followed by one
acknowledge bit. The acknowledge bit is a HIGH level put
on the bus by the transmitter whereas the master
generates an extra acknowledge related clock pulse.

A slave receiver which is addressed must generate an
acknowledge after the reception of each byte. Also a
master must generate an acknowledge after the reception
of each byte that has been clocked out of the slave

transmitter. The device that acknowledges has to pull
down the SDA line during the acknowledge clock pulse, so
that the SDA line is stable LOW during the HIGH period of
the acknowledge related clock pulse, set-up and hold
times must be taken into account.

A master receiver must signal an end of data to the
transmitter by not generating an acknowledge on the last
byte that has been clocked out of the slave. In this event
the transmitter must leave the data line HIGH to enable the
master to generate a stop condition.

Fig.7 Acknowledgment on the I

C-bus.

MBC602

START

CONDITION

clock pulse for

acknowledgement

not acknowledge

acknowledge

DATA OUTPUT

BY TRANSMITTER

DATA OUTPUT

BY RECEIVER

SCL FROM

MASTER

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

7.2

Interrupt (see Figs 12 and 13)

The PCF8574 provides an open drain output (INT) which
can be fed to a corresponding input of the microcontroller.
This gives these chips a type of master function which can
initiate an action elsewhere in the system.

An interrupt is generated by any rising or falling edge of the
port inputs in the input mode. After time t

the signal INT is

valid.

Resetting and reactivating the interrupt circuit is achieved
when data on the port is changed to the original setting or
data is read from or written to the port which has generated
the interrupt.

Resetting occurs as follows:

In the READ mode at the acknowledge bit after the rising
edge of the SCL signal

In the WRITE mode at the acknowledge bit after the
HIGH-to-LOW transition of the SCL signal

Interrupts which occur during the acknowledge clock
pulse may be lost (or very short) due to the resetting of
the interrupt during this pulse.

Each change of the I/Os after resetting will be detected
and, after the next rising clock edge, will be transmitted as
INT. Reading from or writing to another device does not
affect the interrupt circuit.

7.3

Quasi-bidirectional I/Os (see Fig.14)

A quasi-bidirectional I/O can be used as an input or output
without the use of a control signal for data direction.
At power-on the I/Os are HIGH. In this mode only a current
source to V

is active. An additional strong pull-up to V

allows fast rising edges into heavily loaded outputs. These
devices turn on when an output is written HIGH, and are
switched off by the negative edge of SCL. The I/Os should
be HIGH before being used as inputs.

handbook, full pagewidth

MBD976

MICROCOMPUTER

INT

PCF8574

(1)

PCF8574

(2)

V DD

INT

PCF8574

(16)

Fig.12 Application of multiple PCF8574s with interrupt.

Fig.13 Interrupt generated by a change of input to I/O P5.

handbook, full pagewidth

MBD972

start condition

R/W

acknowledge
from slave

SDA

SCL

DATA INTO

t ir

INT

slave address (PCF8574)

data from port

stop

condition

t iv

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134).

HANDLING

Inputs and outputs are protected against electrostatic discharge in normal handling. However, to be totally safe, it is
desirable to take precautions appropriate to handling MOS devices. Advice can be found in Data Handbook IC12 under
"Handling MOS Devices".

10 DC CHARACTERISTICS

= 2.5 to 6 V; V

= 0 V; T

amb

40 to +85

C; unless otherwise specified.

SYMBOL

PARAMETER

MIN.

MAX.

UNIT

supply voltage

0.5

+7.0

input voltage

0.5

+ 0.5

DC input current

DC output current

supply current

100

supply current

100

tot

total power dissipation

400

power dissipation per output

100

stg

storage temperature

+150

amb

operating ambient temperature

+85

SYMBOL

PARAMETER

CONDITIONS

MIN.

TYP.

MAX.

UNIT

Supply

supply voltage

2.5

6.0

supply current

operating mode; V

= 6 V;

no load; V

= V

or V

;

SCL

= 100 kHz

100

stb

standby current

standby mode; V

= 6 V;

no load; V

= V

or V

2.5

POR

Power-on reset voltage

= 6 V; no load;

= V

or V

; note 1

1.3

2.4

Input SCL; input/output SDA

LOW level input voltage

0.5

+0.3V

HIGH level input voltage

0.7V

+ 0.5

LOW level output current

= 0.4 V

leakage current

= V

or V

input capacitance

= V

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

Note

1. The Power-on reset circuit resets the I

C-bus logic with V

< V

POR

and sets all I/Os to logic 1 (with current source

to V

I/Os

LOW level input voltage

0.5

+0.3V

HIGH level input voltage

0.7V

+ 0.5

IHL(max)

maximum allowed input
current through protection
diode

or V

400

LOW level output current

= 1 V; V

= 5 V

HIGH level output current

= V

300

OHt

transient pull-up current

HIGH during acknowledge
(see Fig.14); V

= V

;

= 2.5 V

input capacitance

output capacitance

Port timing; C

100 pF (see Figs 10 and 11)

output data valid

input data set-up time

input data hold time

Interrupt INT (see Fig.13)

LOW level output current

= 0.4 V

1.6

leakage current

= V

or V

IMING

; C

100

input data valid time

reset delay time

Select inputs A0 to A2

LOW level input voltage

0.5

+0.3V

HIGH level input voltage

0.7V

+ 0.5

input leakage current

pin at V

or V

250

+250

SYMBOL

PARAMETER

CONDITIONS

MIN.

TYP.

MAX.

UNIT

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

11 I

C-BUS TIMING CHARACTERISTICS

Note

1. All the timing values are valid within the operating supply voltage and ambient temperature range and refer to V

and V

with an input voltage swing of V

to V

SYMBOL

PARAMETER

MIN.

TYP.

MAX.

UNIT

C-

BUS TIMING

(see Fig.15; note 1)

SCL

SCL clock frequency

100

kHz

tolerable spike width on bus

100

BUF

bus free time

4.7

SU;STA

START condition set-up time

4.7

HD;STA

START condition hold time

4.0

LOW

SCL LOW time

4.7

HIGH

SCL HIGH time

4.0

SCL and SDA rise time

1.0

SCL and SDA fall time

0.3

SU;DAT

data set-up time

250

HD;DAT

data hold time

VD;DAT

SCL LOW to data out valid

3.4

SU;STO

STOP condition set-up time

4.0

Fig.15 I

C-bus timing diagram.

handbook, full pagewidth

PROTOCOL

SCL

SDA

MBD820

BIT 0

LSB

(R/W)

t HD;STA

SU;DAT

HD;DAT

VD;DAT

t SU;STO

BUF

SU;STA

LOW

t HIGH

1 / f SCL

START

CONDITION

(S)

BIT 7

MSB

(A7)

BIT 6

(A6)

ACKNOWLEDGE

(A)

STOP

CONDITION

(P)

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

13 SOLDERING

13.1

Introduction

There is no soldering method that is ideal for all IC
packages. Wave soldering is often preferred when
through-hole and surface mounted components are mixed
on one printed-circuit board. However, wave soldering is
not always suitable for surface mounted ICs, or for
printed-circuits with high population densities. In these
situations reflow soldering is often used.

This text gives a very brief insight to a complex technology.
A more in-depth account of soldering ICs can be found in
our

"IC Package Databook" (order code 9398 652 90011).

13.2

DIP

13.2.1

OLDERING BY DIPPING OR BY WAVE

The maximum permissible temperature of the solder is
260

C; solder at this temperature must not be in contact

with the joint for more than 5 seconds. The total contact
time of successive solder waves must not exceed
5 seconds.

The device may be mounted up to the seating plane, but
the temperature of the plastic body must not exceed the
specified maximum storage temperature (T

stg max

). If the

printed-circuit board has been pre-heated, forced cooling
may be necessary immediately after soldering to keep the
temperature within the permissible limit.

13.2.2

EPAIRING SOLDERED JOINTS

Apply a low voltage soldering iron (less than 24 V) to the
lead(s) of the package, below the seating plane or not
more than 2 mm above it. If the temperature of the
soldering iron bit is less than 300

C it may remain in

contact for up to 10 seconds. If the bit temperature is
between 300 and 400

C, contact may be up to 5 seconds.

13.3

SO and SSOP

13.3.1

EFLOW SOLDERING

Reflow soldering techniques are suitable for all SO and
SSOP packages.

Reflow soldering requires solder paste (a suspension of
fine solder particles, flux and binding agent) to be applied
to the printed-circuit board by screen printing, stencilling or
pressure-syringe dispensing before package placement.

Several techniques exist for reflowing; for example,
thermal conduction by heated belt. Dwell times vary
between 50 and 300 seconds depending on heating
method. Typical reflow temperatures range from
215 to 250

Preheating is necessary to dry the paste and evaporate
the binding agent. Preheating duration: 45 minutes at
45

13.3.2

AVE SOLDERING

Wave soldering is not recommended for SSOP packages.
This is because of the likelihood of solder bridging due to
closely-spaced leads and the possibility of incomplete
solder penetration in multi-lead devices.

If wave soldering cannot be avoided, the following
conditions must be observed:

A double-wave (a turbulent wave with high upward
pressure followed by a smooth laminar wave)
soldering technique should be used.

The longitudinal axis of the package footprint must
be parallel to the solder flow and must incorporate
solder thieves at the downstream end.

Even with these conditions, only consider wave
soldering SSOP packages that have a body width of
4.4 mm, that is SSOP16 (SOT369-1) or
SSOP20 (SOT266-1).

During placement and before soldering, the package must
be fixed with a droplet of adhesive. The adhesive can be
applied by screen printing, pin transfer or syringe
dispensing. The package can be soldered after the
adhesive is cured.

Maximum permissible solder temperature is 260

C, and

maximum duration of package immersion in solder is
10 seconds, if cooled to less than 150

C within

6 seconds. Typical dwell time is 4 seconds at 250

A mildly-activated flux will eliminate the need for removal
of corrosive residues in most applications.

13.3.3

EPAIRING SOLDERED JOINTS

Fix the component by first soldering two diagonally-
opposite end leads. Use only a low voltage soldering iron
(less than 24 V) applied to the flat part of the lead. Contact
time must be limited to 10 seconds at up to 300

C. When

using a dedicated tool, all other leads can be soldered in
one operation within 2 to 5 seconds between
270 and 320

1997 Apr 02

Philips Semiconductors

Product specification

Remote 8-bit I/O expander for I

C-bus

PCF8574

14 DEFINITIONS

15 LIFE SUPPORT APPLICATIONS

These products are not designed for use in life support appliances, devices, or systems where malfunction of these
products can reasonably be expected to result in personal injury. Philips customers using or selling these products for
use in such applications do so at their own risk and agree to fully indemnify Philips for any damages resulting from such
improper use or sale.

16 PURCHASE OF PHILIPS I

C COMPONENTS

Data sheet status

Objective specification

This data sheet contains target or goal specifications for product development.

Preliminary specification

This data sheet contains preliminary data; supplementary data may be published later.

Product specification

This data sheet contains final product specifications.

Limiting values

Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress above one or
more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation
of the device at these or at any other conditions above those given in the Characteristics sections of the specification
is not implied. Exposure to limiting values for extended periods may affect device reliability.

Application information

Where application information is given, it is advisory and does not form part of the specification.

Purchase of Philips I

C components conveys a license under the Philips' I

C patent to use the

components in the I

C system provided the system conforms to the I

C specification defined by

Philips. This specification can be ordered using the code 9398 393 40011.

Internet: http://www.semiconductors.philips.com

Philips Semiconductors a worldwide company

Š Philips Electronics N.V. 1997

SCA53

All rights are reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner.

The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed
without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor imply any license
under patent- or other industrial or intellectual property rights.

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Printed in The Netherlands

417067/1200/02/pp24

Date of release: 1997 Apr 02

Document order number:

9397 750 01758

Part Number PCF8574