main feature

◎Line/voice circuit, LD/MF reserve dialer and ringtone on a 28-pin CMOS chip

◎ Operating range 13 to 100 mA (down to 5 mA with reduced performance)

◎Soft cut to avoid serious deformation

◎Receive signal volume control

◎Line loss compensation can be selected by pin

◎Low noise (max -72 dBmp)

◎Real impedance or complex impedance

◎Net 4 compatible

◎LD/MF switchable dial

◎Pacifier sound when programming

◎31 last number redial

◎ Reserve memory (non- AS2534 ), 4 direct/10 indirect (AS2533/6), 12 direct (AS2535)

◎Busy or busy repeat dialing (non-AS2535)

◎Slide cursor protocol with comparison

◎Pause button to enter pause or wait function

◎3 flashes, 100ms, 280ms and 375 / 600ms

◎On-chip MF filter (compatible with CEPT CS 203)

◎Ring frequency identification

◎Three-tone melody generator

General Instructions

The AS253x is a CMOS integrated circuit that contains all the functions required to form a high-performance electronic telephone.

The device includes LD/MF track dialing, melody generation, ring frequency resolution and quality line/voice circuitry.

There is a RAM on the chip for 31 digits of redial and memory (not AS2534), each memory contains up to 21 digits/data. The sliding cursor process makes the LNR function simple and suitable for various PABX systems. Also offers centrex keys (not AS2535).

The device includes a headphone volume control. The volume can be controlled by the volume keys (+5.4dB) or by pressing the –/+ keys (+8.1dB/-5.4dB in 5 steps).

The versatility of the circuit is provided by pin options as well as some external components. Doing so is easy to adapt to different PTT requirements.

pack

Available in 28-pin SOIC or DIP.

block diagram

Selection overview

Keyboard connection (volume keys or +/– keys)

Key closed, RON max = 1 kohm open

Key on, ROFF min=1 Mohm off

For AS2534E, P/M is the MT key.

Keyboard connection (volume keys or +/– keys)

power-on reset

An on-chip power-on-reset circuit monitors the supply voltage (VDD) during off-hook. When VDD rises above about 1.2V, a power-on reset occurs, clearing the RAM.

DC condition

The normal operating range is 13mA to 100mA. The reduced performance operating range is from 5mA to 13mA (parallel operation). Within the scope of work, all functions work.

When the line current falls below 13mA, the AS253x provides an additional slope below 4.5V to allow parallel operation (see Figure 13).

The DC characteristics (excluding the diode bridge) are determined by the LI voltage and resistor R1 when the line current is above 13 mA, as follows:

The voltage of LI is 4.5V in the normal operating range.

During pulse dialing, the voice circuits and other parts of the device do not work and are in a power-down mode to save current. The CS pin is pulled to V in order to turn on the external shunt transistor to maintain a low voltage drop on the LS pin during turn-on.

AC impedance

The AC impedance of the circuit is set by external components. Impedance can be real or complex. The AC impedance is determined as follows:

The DC value of Z1 should be 30Ω to maintain correct DC performance.

Return loss and sidetone cancellation can be determined independently of each other.

voice circuit

The voice circuit consists of transmit and receive channels, with dual soft limiting, mute, line loss compensation and sidetone cancellation.

transmission

The transmission path gain from M1/M2 to the 600Ω line termination of LS is 37 dB (see Test Circuit Figure 10).

The microphone input is not the same as the 20 kΩ input impedance.

The soft-clamp circuit limits the output voltage of the LI to 2V (see Figure 12). The attack time is 30μs/6db, and the decay time is 20ms/6db. When mute is active, the gain is reduced by >60dB during dialing or after pressing the P/M key.

take over

For a 600Ω line termination, the receive path has a gain of 3 dB (Test Circuit Figure 10). The receive input is the differential signal of RI and STB. When mute is active during dialing, the gain will be reduced by >60dB. During DTMF dialing, the receiver will emit a comfortable DTMF tone. The comfort tone is a DTMF signal of -30 dB relative to the line signal.

Press the volume keys to change the receive gain. The VOL key provides +5.4db of boost and has a toggle function, i.e. suppressing the key resets the gain to default. Another option is to use the "+/– keys". + key increases gain by 8.1db in 3 steps, – key decreases gain by 5.4db in 2 steps (total range 13.5db). On the AS2533/5, the volume will be reset to default on the next hookup; on the AS2534/6, the volume setting will remain at the last setting. POR always resets the volume to default.

The soft-clamp circuit limits the voltage at the receive output (RO) to 1V (see Figure 11). It prevents severe distortion and sonic shock.

side tone

A good sidetone cancellation is achieved by using the following equation:

The sidetone cancellation signal is applied to the STB input.

Line loss compensation

Line loss compensation is a pin selection. When it is activated, the transmit and receive gain is reduced by 6dB at line currents of 20 to 50mA when LLC=a, and by 45 to 75mA when LLC=high (@R1 =30Ω). When LLC=low, line loss compensation is disabled (see Figures 4 and 5).

Dial function

valid key

Key scan is enabled when HS/DPN is pulled high and V is higher than V. Valid keys are detected from the keyboard by connecting the appropriate row to the column (R < 1 kΩ). This can be done by using an nxm keyboard matrix and a single contact. Four diodes are used to extend the number of rows (see Keypad Arrangement Figure 2). It is also possible to connect μcontrollers to rows and columns (see application note AN3010).

P/M and MT keys

Button (not AS2534E) for program/mute and mute button (AS2534E only). Pressing the button silences the voice circuit and the device is programmed. Press this key to disable mute and program status (toggle function). This key works similarly, but has no program function. Powder Metallurgy MTP/MP/MMT LED light on when program/mute is active (flashing: 80ms "on" and 1 second "off").

Dial mode selection

The default mode (LD or MF) can be selected by the mode pin. Temporary changes to MF can be invoked by pressing the T/P key (not AS2535) or the * key (generate MF tone with the first * key entry when mode pin = line 5) when the default LD mode is selected. By suppressing the T/P key (not AS2535) or pressing the R (R1, R2 or R3) key or the next hook, the circuit will revert to LD.

When the mode pin selects MF mode, the circuit cannot temporarily change to LD, but will remain in MF mode.

Centrex key (not AS2535)

Alphanumeric keys facilitate the use of centrex services. A, B, C and D keys are only valid in MF mode (including temporary MF) and cannot be stored. Pressing one of the keys will recall the corresponding MF tone to be transmitted.

The centrex key is not stored in RAM, and subsequently entered numbers are buffered in the FIFO.

redial

LNR is a device that allows to re-sign the last manually dialed number without having to type all the digits again. The LNR is repeatable after each decoupling.

The current contents of RAM are overwritten with new entries.

Manually entered numbers are automatically stored in the LNR RAM. The capacity of RAM is 31 bits. If the entered number is greater than 31 bits, the LNR device will be disabled (until the new entry is less than 32 bits) and more entries will be buffered in the FIFO.

Pause can be inserted by key (not AS2535). P.S. Dial-after digits, i.e. numbers entered manually after calling the LNR, are not stored in RAM, but buffered in FIFO.

Repeat dialing (not AS2535)

The last manually dialed number can be repeated by pressing the RP key without hooking up. If the called number is connected, pressing the RP key will disconnect the line for 1.6 seconds (to get a new dial tone), the number will be repeated after a pause.

When a number is dialed before the RP key is pressed, the repeat function is enabled and it can be recalled indefinitely until the next hang. During the 1.6 second disconnection, the device is in power-down mode to save current.

recall function

Calling (R1, R2 or R3 key) to activate will call the flash (timing loop interrupt), however, the R1 flash never executes in LD mode. R2 and R3 will execute independently of the mode.

If the callback is the first entry in the number string, it will be stored in LNR RAM when the number is entered after the callback.

If the recall key is pressed after a string of digits has been entered or dialed, the call will not be stored, but instead buffered in the FIFO with the subsequently entered digits.

If there is no numeric input after pressing the recall key, the LNR RAM remains intact.

After recall, a pause of 270 ms is automatically performed.

Memory keys (not AS2534)

The keys are direct memory access keys, and the keys (AS2533/6 only) are used for abbreviated dialing.

Memory arrangement AS2533/6 AS2534 AS2535

Store number 14 0 12

Direct memory keys 4 0 12

Indirect memory 10 0 0

In the on-chip RAM, numbers can be stored. Each number can contain up to 21 digits (including pauses).

During programming, multiple pauses can be inserted by pressing (not the AS2535) or key. Each pause inserted in the first 5 entries will automatically terminate after 2 seconds, while a pause inserted after position 5 in the digit string will stop dialing and can be terminated manually by pressing (not AS2535) or the key. The halt feature allows dialing to an extension on the PABX.

Example (45678 – 123 are stored in M1, where – is pause/wait and 123 is the extension number):

Hang up, wait for dial tone; press M1 (dial 45678); wait for dial tone from the called PABX; press PS or LNR (dial 123).

Memory dials are cascaded. However, the contents of one memory must be allocated before a new memory can be called.

Slide cursor process

To accommodate the simple and easy redialing (LNR) behind PABX, the sliding cursor protocol is implemented. If the new entry matches the previous RAM contents, the key will dial out the remaining digits.

If there is an error in the match, the LNR will be disabled until the next mount and the RAM will contain the new number.

Example (LNR content 912345, where 9 is the access code):

Go off-hook, wait for PABX dial tone press 9, wait for external dial tone press LNR (12345 will be dialed).

audio generator

The tone generator contains 3 fundamental frequencies of DTMF tones, bells and soothing tones.

DTMF

The DTMF generator provides 8 frequencies, namely:

low grouping

Digital 1-2-3-A 697 Hz

Digital 4-5-6-B 770 Hz

Digital 7-8-9-C 852 Hz

digit*-0-#-D 941 Hz

high grouping

Digits 1-4-7-* 1209 Hz

Digital 2-5-8-0 1336 Hz

Numbers 3-6-9-# 1477 Hz

Digital ABCD 1633 Hz (not AS2535)

The MF output level can be set via an external voltage divider on pin MFL.

Pin MFL(2) DTMF level voltage (low group)

1.50V (AGND) -4.0dBm

1.27V -5.2dBm

1.15V -6.4dBm

1.03V -7.6dBm

0.90V -8.8dBm

0.70V -10.0dBm

0.54V -11.2dBm

0.42V -12.4dBm

0.30V -13.6dBm

0.18V -14.8dBm

0.00V (vehicle speed) -16.0 dBm (ZLINE=600 ohms)

The prephase is 2.6db.

MF tones comply with CEPT recommendations.

Ringtone (melody/volume)

The three fundamental frequencies of a melody are:

The repetition rate and volume of the ringtone melody can be programmed by pressing P/M and # followed by a number (not AS2534E):

End the process by suppressing the P/M key.

The default setting is number 6, i.e. after a power-on reset, the device will start at repetition rate 4 and maximum volume. If the number 0 is programmed, the bell will turn off until the next hook is disconnected, returning to the last setting before 0. Programming settings are stored in on-chip RAM.

Repetition rate refers to the sequence of 6 frequencies repeated 1, 4 or 10 times in 1 second.

The frequency sequence is controlled by the sequence register as follows: sequence F1 F2 F3 F1 F2 F3…

AS2534E is fixed at default settings and cannot be programmed to other settings.

soothing tone

With MF dialing, DTMF tones are provided to the handset as comfort tones.

During programming, key input is confirmed by a 1477 Hz soothing tone. At the reverse osmosis output, the level of the pacifier tone is about 60 mV. After each entry into programming mode, the duration is 40 milliseconds.

Provides a 140 ms confirmation tone when programming mode is terminated with the P/M key. However, an invalid key entry would result in the termination of the program mode indicated by 4x 40 ms rejection tones, with a 28 ms pause between tone bursts.

Ring frequency resolution

The ring discriminator ensures that only signals with frequencies between 13Hz and 70Hz are considered valid ring signals. The time to identify a valid loop signal is 1/f second, where "f" is the loop frequency.

The melody generator is activated when a valid ring signal persists for 73 ms and remains active as long as the ring signal is present.

Once the melody generator is activated, the bell signal will be continuously monitored and the melody generator will turn on or off immediately (until the next POR or off hook) depending on the momentary presence of a valid or unverified bell signal.

Typical Characteristics of Line Loss Compensation

AC Model of Speech Circuits

typical application

Complex impedance (270Ω+750Ω/150 nF)

The components needed to demonstrate the full functionality of the AS253X are included. External components may be altered to comply with various national PTT regulations and interface with different sensors. Since the AS253x is an assembly, not a complete system, it cannot be approved by a standards body as a stand-alone part. Therefore, full compliance with any standard depends on the application in which the AS253x is used, therefore, approval by the standards body is the responsibility of the customer, and Mikro Systeme Austria will not test products for compliance with specific standards. For more application information, please refer to Application Instructions AN2201.

operating procedure

procedural principles

Programs utilizing the features of the AS253x are optimized without regard to human factors in order to:

- Meet user expectations

- Easy to learn and easy to learn

- Does not invoke any automatic functions that the user does not expect

- Protect users from major mistakes such as dialing the wrong number, deleting stored numbers, etc.

- Consistent and simple to use.

The following pages describe the operating steps for the provided functions. Pressing an unauthenticated key or key combination during programming will cause the device to abort the programming state. Pressing any key combination or sequence not described or defined may cause the device to enter a state or mode not intended by the user. In this case, any undesired state can be terminated at any time by on/off hook, which will generate a functional reset.

Programming Ringtones (Non-AS2534E)

*) When the number 0 (ringer off) is programmed, the device will automatically return to the previous setting (different from 0) through the next hookup.

Temporary MF

When mode pin = row 5, pressing the * key also selects the send tone via MF. Either the T/P key (not AS2535) or the * key can be used.

Characteristic Curve (Typical)

application:

For application support, please contact your local sales office.