Data Sheet

AS2574B

Rev. 1

Jan. 1995

Package

Available in 28 pin DIP and PLCC.

20 NUMBER ONE TOUCH DIALLER WITH

SERIAL BUS FOR DISPLAY DRIVER

Austria Mikro Systeme International

Key Features

Low operating voltage (2.5V to 5.5V)

Low current consumption (typ. 200

A in LD mode)

Oscillator using ceramic resonator (681 kHz)

MF level independent of supply voltage

Direct ´wake-up´ from keyboard

Automatic Call Progress by direct memory key

Data protection with 8 digit FIFO

Sliding cursor protocol with comparison

Diode options for different PTT requirements

Automatic pause generation after access code

Temporary MF select via keyboard

36 digit LNR (Last Number Redial)

20 memories addressable with direct keys and the

2nd key or indirect with a MEM key

Notepad

Serial interface to display driver AS2590

Consistent, simple and useable procedures

Input for dial tone recognizer

General Description

The AS2574B is an integrated CMOS device for feature
telephones. It is a very versatile LD/MF dialler with serial
interface to a display driver. The device is designed to be
used in a wide variety of applications together with the
companion display driver, AS2590.

The on chip RAM can contain up to 20 memories (each
with maximum 18 digits), a 36 digit Last Number Redial
(LNR) and an 18 digit notepad. Access to the 20 memo-
ries is either with direct keys, abbreviated dial code or a
combination of both. The AS2574B provides a unique
feature, Automatic Call Progress (ACP), on all memory
keys, i.e. the circuit automatically seizes the line and
waits for the dial tone and dials the number just by
pressing any of the memory keys (including LNR).

The circuit features 2 different access code procedures
to allow easy use under a PABX. A dial tone input
enables the use of a dial tone recognizer.

SDA

SCL

C4
C3

TONE

Vss

AS2574B

DIALLER/CONTROLLER

L a

M 4

M 8

M 7

M 6

M 5

M 2

M 1

M 3

MASK

OSC1

OSC2

681kHz

M U T E

E N T E R

2 N D

M 1 0

M E M

M 9

LNR

L S

SDA

SCL

V23

V13

LCD

BIAS

Vss

AS2590

32.768kHz

DISPLAY

MODE

ACP

M/B

Flash

Ground
Loop

S P E E C H

LOUDHEARING

HANDSFREE

TONE RINGER

Application

High feature telephone sets.

Direct wake-up is an AMS patented

solution providing line seizing with

a telephone, that is entirely

powered from the telephone line,

by pressing a key in a key matrix

connected to a dialler/controller

that is constantly connected to the

line by means of a line voltage

limiter and yet maintaining a high

dc isolation resistance in idle state

(on-hook).

The wake-up feature allows the

user to go off-hook by pressing a

direct memory key or a

loudspeaker key, so-called on-

hook dialling or call progress

monitoring, and thereby seize the

line.

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Pin #

Pin Node

Description

OSC2

Oscillator pins for ceramic resonator (681 kHz)

OSC1

SCL

The SCL output is used to clock all data into the display driver

SDA

The SDA output is used to transfer data into the display driver

5 - 10

C1 - 6

Keyboard columns

11 - 15

R1 - 5

Keyboard rows

Output for controlling loudhearing and handsfree facilities, active high

(see hook state diagramme)

MASK

Mask output, active high during pulsing (make and break period, see timing

diagrammes).

Chip disable input, active low.

When CD is low, the circiut is disabled.

If this pin is pulled to V

during Off-hook (indicating a disconnect) for more than

2 sec., the circuit is reset*. If the pin is pulled to V

for less than 2 sec., the

line break is ignored.
* If in ACP or monitor state, reset also means return to idle state.

Mute output, active high during signalling (see timing diagrammes).

Transmit mute output, active high when MR is high and when

the Mute key has been activated (see timing diagrammes).

Earth recall input/output, active high during ER but when forced to V

the flash is enabled.

Dial tone input.

This input is scanned when invoking ACP or a pause is read in a digit string:

DT pin

Function

Open

Pause duration 4.1 sec

Low

If a high is not detected within 8 sec., the circuit is

reset *

High

If the pin is high for > 1.15 sec., the pause is termi-

nated and the dialling continued. Noise immunity > 8 ms

* Reset means that dialling is stopped and the circuit returns to standby.

If the circuit was in ACP state, the reset will also return the circuit to idle state.

Hook switch control, dial pulse and flash output; low during Idle and break

periods and high during off-hook (see timing diagrammes).

Pin Description

Continues...

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Pin Description Continued

Pin #

Pin Node

Description

Hook switch input; active high with internal pull-down resistor. Debounce 25 ms.

Vss

Negative terminal of power supply.

Tone burst output:

LS high

80 ms burst, 8 sec pause

MT high

80 ms burst, 2 sec pause

Only in speech mode

MT+LS high

80 ms burst, 2 sec pause

TONE

MF tone output.

An on chip reference voltage provides tone levels independent of the

supply voltage.
A dc path from TONE output is needed to accommodate an external voltage
divider for setting the appropriate tone level.

Frequencies:

Frequency (Hz)

Key Matrix (Hz)

Error (%)

697

row 1

770

row 2

852

row 3

941

row 4

1209

col. 1

0.7%

1336

col. 2

1477

col. 3

1633

see p. 7

Vdd

Positive terminal of power supply

RECALL

L S

LNR

2ND

MUTE

COLUMN

ROWS

The keyboard is arranged in a 5 x 6 contact matrix with single pole single throw
contacts (SPST).
Keyboard resistance: Ron < 5 k

; Roff > 5 M

ENTER

MEM

M10

Enabled only
when off-hook

Enabled also
when ACP is
active (diode 5
inserted)

Enabled when
CD = high

In off-hook state all keys are
enabled (CD = high)

Keyboard Layout

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Power On Reset

The on chip analogue power on reset circuit monitors the
supply voltage (V

). As long as V

remains below the

internal reference voltage, V

REF

(typically 1.2V), the

oscillator is inhibited. When V

rises above V

REF

, a reset

signal is generated to assure correct start-up, and the
oscillator is enabled.

The correct start-up/reset condition of the circuit is
guaranteed regardless of the absolute and chronologi-
cal rise time of V

, CD and HS inputs.

Line Supervision

In off-hook condition the device performs supervision of
the line current disconnects in the following manner:
Line disconnects (CD low) of less than 2 sec. are ignored
and the device continues operation.
Line disconnects of more than 2 sec. cause stop of
dialling and the circuit is switched to standby mode if HS
is high, otherwise the circuit will return to idle mode.

Mode Selection

The default mode (LD or MF) can be selected by the
diode option mode (diode 6).

When default LD mode is selected, a temporary change
to MF mode can be invoked by pressing the * key.

When the circuit is in temporary MF mode, each of the

Mute Key

Depressing the Mute key activates and deactivates
(toggle switch) the MT output, when internal mute is
inactive, i.e. when no data is being read from the RAM or
FIFO.

A change of the hook state will release the mute.

Valid Keys

A valid key is detected from the keyboard by connecting
the appropriate row to the column. This can be done
using an n x m keyboard matrix with single contacts.
Positive and negative edges of each contact are de-
bounced. The debounce time is 15 ms.

In idle state (on-hook) only the LS key is always valid
independent of the CD pin. When diode 5 is connected,
also the LNR, MEM, and M1 - 9 keys are valid entries
invoking ACP (automatic call progress).

following procedures revert it to default LD mode:

- pressing R key (all subsequently entered digits are

buffered in FIFO),

- by next On-hook.

Last Number Redial

LNR is a facility that allows resignalling of the last
manually dialled number without keying in all the digits
again. The LNR is repeatable.

A manually entered number is automatically stored in the
LNR RAM. The capacity of the RAM is 36 digits. If a
number greater than 36 digits is entered, the LNR facility
will be inhibited (until new entries < 37 digits) and further
entries will be buffered in FIFO. If more than 18 digits are
entered, the display will show the digit 19 and onwards.

Postdialled digits, i.e. digits manually entered after LNR
has been invoked, are not stored in RAM but buffered in
FIFO.

The current contents of the LNR RAM are overwritten by
new entries.

Memory Dial

An on chip RAM enables the dialler to store up to 20
numbers, each containing a maximum 18 digits/data.

The first 10 memories are accessible with 10 Direct dial
keys (M1 to M10) and another 10 memories (11 - 20) are
accessible by pressing the 2nd key before one of the
Direct dial keys or by pressing the MEM key and a digit
0 - 9 (abbreviated dialling).

Basic store procedure:

1 Press Enter key

2 Key in digits, including access code, pauses and recall

as appropriate (number is stored in LNR RAM)

3 Select location by keeping Enter key depressed while

entering the desired location (M1...M10, 2nd
M1...M10, or MEM 0...9)

4 Release Enter key to finish

5 Continue with 1, 2, 3 and 4 for storing further numbers.

Only the first 18 digits/data will be stored when copying
more than 18 digits/data in a memory.

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Recall Function

A recall activation will invoke a flash (timed loop break)
or an earth recall (ER) depending on the ER pin. When
the ER pin is forced to V

, a flash is executed; and when

ER is open (> 50 k

}, an earth recall is executed.

If R is the first entry in a digit string, it will be stored in LNR
RAM.

If the R key is depressed after a digit string has been
dialled out, the recall will not be stored, and subsequently
entered digits will be buffered in the FIFO.

A recall will automatically generate a pause when a recall
is read from a memory and therecall has been stored as
an access code.

A manual invoked earth recall will pull ER high for
minimum 500 ms, but the ER pin is maintained high as
long as the key is depressed.

During auto dial an earth recall is executed with a
duration of 500 ms.

Pause Generation

Pause introduces a delay in signalling digits strings to
accommodate second and subsequent dial tones.

Automatic pauses are generated:

- during dialling out from memories when the first digit(s)

in the digit string equal the stored access code(s)
(pause depends on DT input).

- when going Off-hook by pressing LNR, MEM, or M1 -

9 (ACP).

Any pause can be terminated (shortened) prior to time
out by pressing the LNR key or a high level on the DT
input.

During ACP a pause time out, i.e. DT kept low for > 8
sec., will return the device to idle state.

Pauses are storable as digits within a string of any of the
memories by pressing 2nd # during programming.
Multiple pause entries can be stored up to the maximum
length of the digit string (18 digits/data). A pause is not
accepted in location 1 of a digit string.

If more pauses have been stored in succession, they can
all be terminated by one depression of the LNR key or a
high level on the DT pin for

1.15 sec.

Sliding Cursor Procedure

To accommodate redialling (LNR) behind a PABX wi-
thout using automatic pause generation (storing access
codes), a sliding cursor protocol is implemented. If new
entries match the previous LNR RAM contents, pressing
the LNR key will dial out the remaining digits.

If there is an error in matching, the LNR will be inhibited
until next On-hook, and the LNR RAM will contain the
new number.

Access Codes

Different access codes (totally up to 18 digit/data inclu-
ding spaces) can be stored in one string. Spaces bet-
ween the different access codes are entered by pressing
the 2nd # during programming. Each access code can
contain up to 4 digits.

If one or more access codes are stored, the first entered
digit(s) in a digit string read from the RAM will be
compared with the access code(s) and if equal, a pause
is generated.

Example on programming access codes:

ENTER, 9 , 2nd #, 50

Keep

ENTER

depressed while pressing

Release both

The first access code in this example is 9 and the second
50.

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Symbol/command

MSB

LSB

HEX

Pause

Temporary MF select

Recall

LS on

LS off

MT on

MT off

2nd on

2nd off

Set Clock

Start

Start copy

Start FIFO

Start timer

Blank all

Test mode

Serial Interface

The AS2574B supports a serial bus. The protocol
defines device that sends data onto the bus as a
transmitter, and the receiving device as the receiver. The
AS2574B is controlling the transfer and hence the
master. The display driver, AS2590, being controlled is
the slave.

Clock and Data Conventions
Data states on the SDA line can change only during SCL

low. SDA state changes during SCL high are reserved
for indicating start and stop conditions (see figure 1).

Start Condition
All commands are preceded by the start condition, which
is a high to low transition of SDA when SCL is high.

Stop Condition
All communications are terminated by a stop condition,
which is low to high transition of SDA when SCL is high.

START

BIT

SDA

SCL

BIT 0

BIT 1 ...

... BIT 4

STOP BIT

WORD

GAP

Figure 1: Data Transmission

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Key/Key Combination

Function

Remarks

ENTER

Programming

Flash or ground loop

Code no 19

MEM

Abbreviated dialling

MUTE

Privacy mute

Code no 22/23

Monitor/Handsfree

Code no 20/21

LNR

Last Number Redial

During execution of a pause the LNR key is used

to terminate the pause.

M1 - 10

Direct memory keys

2nd

Second functions

Code no 24

2nd, 1

Code no 11

2nd, 2

Code no 12

2nd, 3

Code no 13

2nd, 4

Code no 14

2nd, *

Enter FIFO

Code no 29

2nd, #

Pause

Code no 17

2nd, M1 - 10

Memories 11 - 20

MEM, 0 - 9

Memories 11 - 20

ENTER, Address*

Displaying content of Memo

ENTER/Address*

Programming

Code no 28 when both keys are released

ENTER/#

Setting clock

Code no 26

2nd, 5 - 9

5 - 9

Code no 6 - 10

2nd, 0

Code no 1

2nd, R

RECALL

Code no 19

2nd, MUTE

Privacy MUTE

Code no 22/23

ENTER/LNR

Clearing LNR

Code no 27

ENTER, ENTER

Displaying Access code

Code no 27

Address means M1 - 10 keys or 2nd, M1 - 10 or MEM, 0 -9 key combinations.

Key Combinations

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Diode Options

System Considerations

The device is intended to be used in telephone instru-
ments, that are permanently on-line, i.e. also when on-
hook the circuit is connected to the telephone line, but in
standby mode (idle) and hence only drawing a small
leakage current from the line.

This implementation offers new features like electronic
hook switch and call progress monitoring (on-hook
dialling).

Call progress monitoring (CPM) means pressing the LS
key will switch the telephone on from standby (direct
´wake-up´from keyboard) and will present the dialling
tones via a loudspeaker without lifting the handset.

Furthermore, it is also possible to invoke the CPM by
pressing the LNR, MEM or M1 - 9 when the ACP
(Automatic Call Progress) is activated (diode 5).

Option

Column

Function

No diode

diode

NoP

Number of Pulses

Standard

Digit 1

Flash Time

101.2 ms

600 ms

Memory Size

M/B

Make/Break Ratio

33/66 ms

40/60 ms

ACP

Automatic Call Progress

yes

MODE

Default Signalling Mode

Procedure Principles

The procedures for utilizing the features of the device are
optimized out of consideration for the human factor
in order to:
- meet the user´s expectations
- be easy to learn and relearn
- not invoke any automatic functions which the user

doesn't expect

- protect the user from committing critical errors, e.g.

dialling wrong numbers, deleting stored numbers, etc.

- be consistent, simple and usable.

Columns

Row 5

MODE

ACP

M/B

NoP

The diode options
are scanned by
POR and low to
high transition on
HS.

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Programming/Notepad

Speech mode

or idle

Speech mode

or idle

Speech mode

During programming
the dial out is inhibited.

10 Direct dial keys, a MEM and a 2nd key are available for addressing up to 20 numbers.
Each number can contain up to 18 digits, including recall and pauses.
Programming a new number will automatically clear the previous.
2nd, # has to be pressed between the different access codes.

change

Digits are entered

in LNR RAM

The content of the LNR RAM
is stored in the selected memory.

Speech mode

Enter

Key in

number

keep Enter
depressed

Enter

Direct dial

(M1 - 10)

2nd

MEM

Digit 0

(access codes)

Digit 0-9

(M11 - 20)

Direct dial

(M11 - 20)

Access code(s)

are displayed

release

Enter

Code no 28

stored

Key in

an address

Content of selected

memory is displayed

Enter

correction

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Parameter

Symbol

Min

Typ

Max

Unit

Condition

Supply Current

Outputs unloaded

Operating except MF

200

250

Operating MF

0.75

Data Retention

=1.8V; note1

Note 1

Input Voltage

Low

Vil

0.3xV

High

Vih

0.7xV

Input Current

Low

Iil

High

Iih

Output Current

Sink

Iol

1.5

Vol = 0.4V

Source

Ioh

Voh = V

- 0.4V

Pull-down Resistor

HS Input

Rhs

CD Input

Rcd

Scanning Current DT

During Pause

Sink

Isl

150

Source

Ish

150

Parameter

Symbol

Min

Typ

Max

Unit

Condition

Operating Temperatur

Top

- 25

Operating Voltage

2.5

3.0

5.5

Retention Voltage

1.8

5.5

Oscillator Frequency

Fosc

681

kHz

Electrical Data

Absolute Maximum Ratings

Recommended Operating Range

DC Characteristics

Default conditions: Recommended Operating Range; V

= 3.0V.

Note 1: Circuit in Idle state (HS = Low and no key activated).

Positive Supply Voltage ...................................................................................................................-0.3V

Input Voltage .......................................................................................................................-0.3V

+ 0.3V

Input Current ................................................................................................................................................

25 mA

Storage Temperature ......................................................................................................................-65

C to +125

Electrostatic Discharge (HBM) ......................................................................................................................

1000V

Data Sheet

AS2574B

Rev. 1

Jan. 1995

Parameter

Symbol

Min

Typ

Max

Unit

Condition

Clock Startup Time

Key Debounce Time

HS Debounce Time

Ths

CD Reset Delay Time

sec

DTMF

Tone Level, High Group

Vol

- 12.4

- 10.9

- 9.4

dBm

RL = 15 k

Preemphasis

2.5

2.8

dBm

RL = 15 k

Distortion

- 26

dBr

RL = 15 k

, note 3

Tone Duration

Ttd

82.3

Note 1

Inter Tone Pause

Titp

82.3

Note 1

Tone Rise/Fall Time

Ttr

Note 2

Dial Rate

pps

Make/Break Period

Tm/Tb

33/66

(diode option)

40/60

Inter Digit Pause

Tidp

753

785

Pre Digit Pause

Tpre

Post Digit Pause

Tpo

Flash

Duration

Tfd

100

101.2

103

No diode 2

600

620

With diode 2

Earth Recall

Duration

500

510

Automatic Access Pause

Tap

Short

4.1

4.2

sec

DT = Hi-Z

Long

7.9

8.1

sec

DT = Low

Termination

1.15

1.2

1.25

sec

DT = High

Mute Overhang

Tmo

182

200

223

MR/MT Hold Over

Tho

Tone Burst

Frequency

700

800

Output Level

Vtb

-13

-11

-9

dBm

Tone Duration

Ttb

Inter Tone Pause (LS)

Titb1

sec

Inter Tone Pause (Mute)

Titp2

1.8

2.2

sec

Time-out

Tto

7.7

8.2

sec

Signalling Characteristics

Defaults conditions: Recommended Operating Range

Note 1: The values are valid during automatic dialling and are minimum values during manual dialling, i.e. the tones will continue

as long as the key is depressed.

Note 2: The rise time is the time from valid key detection (key has been debounced) till the tone amplitude has reached 90 % of its

final value.

Note 3: Relative to high group.

Data Sheet

AS2574B

Rev. 1

Jan. 1995

1995, Austria Mikro Systeme International, Schloss Premstätten, 8141 Unterpremstätten, Austria. Trademarks

Registered

the prior written consent of the copyright owner.

Devices sold by Austria Mikro Systeme are covered by the warranty and patent indemnification provisions appearing in its Term of
Sale. Austria Mikro Systeme makes no warranty, express, statutory, implied, or by description regarding the information set forth
herein or regarding the freedom of the described devices from patent infringement. Austria Mikro Systeme reserves the right to
change specifications and prices at any time and without notice. Therefore, prior to designing this product into a system, it is necessary
to check with Austria Mikro Systeme for current information. This product is intended for use in normal commercial applications.
Applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as
military, medical life-support or life-sustaining equipment are specifically

not recommended without additional processing by Austria

Mikro Systeme for each application.

Part Number AS2574B