Preliminary
AS2525
Rev. 1.3
Page 1
May 1999
Key Features
q
q
Line/speech handsfree circuit, LD/MF repertory
dialler, and tone ringer on one 44 pin CMOS chip
q
q
Operating range from 15 to 100 mA line current
(down to 5 mA with slightly reduced performance)
q
q
All significant parameters programmable with
external EEPROM
q
q
Volume control of receiver signal
q
q
Handsfree function with enhanced voice switching
q
q
Low noise (max. -72 dBmp)
q
q
Unique EMC performance
q
q
LD/MF switchable dialling with temporary MF
mode
q
q
Repertory dialling with last number redial and
memory dialling (8 x 2 direct and 10 indirect)
q
q
Call restriction with PIN code
q
q
Serial interface for EEPROM and LCD driver
q
q
2-tone/3-tone ringer with ring frequency detection
Block Diagramme
General Description
The AS2525 is a CMOS mixed-mode integrated
circuit for use in feature phones, answering machines
and fax machines. It contains an analogue line
interface and speech circuit for a/b terminals,
loudhearing, handsfree, enhanced LD/MF dialler, tone
ringer with dc/dc converter and serial interface to
EEPROM and LCD-driver (AS2591), all in a 44 pin
package. The circuit is fully line powered.
The AS2525 uses an external EEPROM for a 31 digit
last number redial storage and memories for 26
numbers each containing up to 21 digits/data.
The device provides a volume control for the earpiece
and the loudspeaker. The volume can be controlled by
pressing the [V-]/[V+] keys.
The versatility of the circuit is provided by
programming all parameters through an external
EEPROM. This allows easy adaptation to various PTT
requirements worldwide.
Package
Available in 44 pin TQFP.
CS
SS
LI
V
PP
LS
+
+
+
+
V
SS
30
RI
STB
300
Z
BAL
A
GND
V
DD
V
DD
V
DD
+
V
PP
V
PP
M1
M2
M3
M4
LO1
LO2
V
SSA
RECI
RECV
RO
NOISE
DET.
LINE
SENSE
PEAK
DET.
VOICE
SWITCHING
PEAK
DET.
DTMF
MELODY
DEBOUNCE
CPU
DIALLER
DC/DC
CONVERTER
OSCILLATOR
KEYSCANNING
CM
KEYBOARD (C1-4/R1-3)
HS
HF
DM/HM
FCI
DPN
LED
DI DO
CLK
CS1 CS2
V
SS
CI
SUPPLY
V
REF
V
DD
A
GND
A
GND
FT2
CBN
FT1
AS2525
3.58
MHz
Austria Mikro Systeme International AG
Single-Chip Handsfree Phone
CMOS Integrated Circuit
Preliminary
AS2525
Rev. 1.3
Page 2
May 1999
Pin Description
Pin #
Symbol
Type
Description
1
CS2
DO
Chip Select 2
Chip select signal for external LCD driver circuit or 2 mA LED
If signal is not activated, a pull down resistor ( 100 k
) is inserted.
2
DPn
DO
D
ial
P
ulse Output
Digital output which holds the line during off-hook operation or pulls low during
break periods of pulse dialling and flash.
3
HF
DI
H
ands
F
ree Switch Input
This is an Schmitt-trigger input that is pulled high to enable handsfree
operation.
4
HS
DI
H
andSet Switch Input
This is an Schmitt-trigger input that is pulled high by the hook switch to enable
handset or headset operation.
5
FT1
AI
Analogue input pin for connecting a capacitor for offset cancellation.
6
FT2
AI
Analogue input pin for connecting a capacitor for offset cancellation.
7
M4
AI
M
icrophone Input
4
Differential input for the handsfree microphone (electret).
8
M2
AI
M
icrophone Input
2
Differential input for the handset microphone (electret).
9
M3
AI
M
icrophone Input
3
Differential input for the handsfree microphone (electret).
10
M1
AI
M
icrophone Input
1
Differential input for the handset microphone (electret).
11
STB
AI
S
ide
T
one
B
alance Input
Analogue input for side tone cancellation network.
12
CS
AO
C
urrent
S
hunt Control Output
N-channel open drain output to control the external high power shunt transistor
for synthesising ac- and dc-impedance, modulation of line voltage and shorting
the line during make periods of pulse dialling.
13
V
SS
Supply
V
oltage
S
ource
S
ource
Negative Power Supply.
14
LI
AI
L
ine
I
nput
Analogue input used for power extraction and line current sensing.
15
RI
AI
R
eceive
I
nput
Analogue input for ac-separated receive signal.
16
SS
AO
S
upply
S
ource
Control Output
N-channel open drain output to control the external high power source
transistor for supplying (Vpp) the loudspeaker amplifier in off-hook
loudspeaking/handsfree mode.
17
LS
AI
L
ine Current
S
ense Input
Analogue input for sensing the line current.
Preliminary
AS2525
Rev. 1.3
Page 3
May 1999
Pin #
Symbol
Type
Description
18
CI
AI
C
omplex
I
mpedance Input
Analogue input pin for the capacitor to program a complex impedance.
19
RECI
AI
RECeive Input
Analogue input for the handsfree receive path. Should be connected to RO via
a coupling capacitor.
20
RECV
AI
RECeive Voice Switching Input
Analogue input for receive voice switching path.
21
RO
AO
R
eceive
O
utput to
H
andset
Output for driving a dynamic earpiece with an impedance from 150
to 300
.
22
V
DD
Supply
V
oltage
D
rain
D
rain
Positive Power Supply.
23
A
GND
Supply
A
nalogue
G
round
Special ground for the internal amplifiers.
24
CBN
AI
Analogue input pin for connecting a capacitor for background noise monitoring.
25
CM
DO
C
onverter
M
ake Output
This is an output for controlling the external switching converter. During ringing
it converts the ring signal into a 4V supply voltage.
26
V
PP
Supply
Loudspeaker Power Supply
High power supply for the output driver stage.
27
28
LO1
LO2
AO
L
oudspeaker
O
utputs
1/2
Output pins for a 32
( 25 to 50
) loudspeaker.
29
V
SSA
Supply
Power supply pin for LO1-LO2 output amplifier.
30
DM/HM
DI
D
ial
M
ode/
H
eadset
M
ode Switch Input
Digital input for choosing between LD and MF dialling or choosing handset and
headset mode. See "Table 3: Parameter settings" for further details. This pin is
scanned after manual off-hook only.
31
FCI
DI
F
requency
C
omperator
I
nput
This is a Schmitt-trigger input for ring frequency discrimination. Disabled during
off-hook.
32
LED
DO
LED
Output
Digital output for connecting 2 mA LED to indicate handsfree mode.
33
OSC
O
scillator Input
Input for ceramic resonator 3.58 MHz.
34
35
36
R1
R2
R3
DI/O
Keyboard
R
ows
(see Figure 4: Keyboard Layout).
37
38
39
40
C1
C2
C3
C4
DI/O
Keyboard
C
olumns
(see Figure 4: Keyboard Layout).
41
CLK
DO
Cl
oc
k
Clock output for 3-wire bus.
If signal is not activated, a pull down resistor (100 k
) is inserted.
Preliminary
AS2525
Rev. 1.3
Page 4
May 1999
Pin #
Symbol
Type
Description
42
DI
DI
D
ata
Input
Data input of 3-wire bus.
If signal is not activated, a pull down resistor (100 k
) is inserted.
43
DO
DO
D
ata
Output
Data output of 3-wire bus.
A 100 k
resistor connected from this pin to VSS enables key locking.
If signal is not activated, a pull down resistor (100 k
) is inserted.
44
CS1
DO
C
hip
Select 1
Chip select signal for external EEPROM.
If signal is not activated, a pull down resistor (100 k
) is inserted.
DI:
Digital Input
AI:
Analogue Input
DO:
Digital Output
AO:
Analogue Output
DI/O:
Digital Input/Output
AI/O:
Analogue Input/output
Pin Configuration
YYWWAAA
AS2525
Austria
CS2 1
DPn 2
HF 3
HS 4
FT1 5
FT2 6
M4 7
M2 8
M3 9
M1 10
STB 11
CS 12
VSS 13
LI 14
RI 15
SS 16
LS 17
CI 18
RECI 19
RECV 20
RO 21
VDD 22
33 OSC
32 LED
31 FCI
30 Head
29 VSSA
28 LS2
27 LS1
26 VPP
25 CM
24 CBN
23 AGND
Figure 3: Pin configuration
Keyboard Layout
C4
C3
C2
C1
4
2
0
7
5
3
8
6
9
MR
R/P
FL
M5
1
M6
PG
V+
M7
V-
M8
#
M1
M2
M3
M4
SH
R1
R2
R3
MT
Figure 4: Keyboard Layout
Maximum R
ON
for key closure: 1 k
Minimum R
OFF
for open key: 1 M
See "Table 1: Key definitions" for description of key
functions.
Basic Definitions
Password is set to 0123 and is used to access basic parameter settings (see Table 3: Parameter settings). The
set-up programming is normally done in the factory during manufacturing of the telephone sets. The factory
settings can be loaded into the EEPROM (see Figure 6: Memory allocation for external EEPROM).
PIN code is default set to 1111 and is used by the user to protect certain user settings (see Table 5: User
programming with PIN code). The PIN code can be changed by the user.
Default settings are shown in bold.
Program procedures are entered with the [PG] key. Pressing any invalid key or going on-hook during programming
will abort the program mode and no changes will be stored. Ending a program procedure by pressing the [PG] key
will store the changes and exit the program mode.
Preliminary
AS2525
Rev. 1.3
Page 5
May 1999
Key Definitions and Procedures
Table 1: Key definitions
Key
Condition
Function
Remark
[0] - [9],
[#], [
]
Off-hook
Digits
Function depending on mode
[
]
LD mode
Temporary MF select
Providing mixed mode dialling (default LD
selected)
[PG]
Speech mode
Enter programme state
To enter the programme state
Programme mode
Exit programme state
To terminate/exit programme state
[MT]
Speech mode
Enter mute state
To enter mute state
Mute state
Exit mute state
To terminate/exit mute state
Programme mode
Enter blank
To enter blank digit during programming
[R/P]
Redial/Pause
Allows re-signalling of the last dialled number and
insertion of pauses
Programme state
Pause
Each key pressure inserts a pause
[FL]
Flash function
Invokes a timed loop break
[V+]
Speech mode
Volume control
To increase the receive gain
[V-]
Speech mode
Volume control
To increase or decrease the receive gain
[MR]
Memory redial key
To access memory by key codes
[M1] - [M8]
Memory dial
Access keys to memories 1 to 8 and 9 to 16
[SH]
Second function (shift)
To access second function of keys
Table 2: Digits
Digit Key
DTMF Mode
(f
LOW
+ f
HIGH
)
Pulse Mode
Programming Mode
([PG] + Digit)
Memory Location
([MR] + Digit)
[0]
941 + 1336 Hz
10 pulses
Memory 17
[1]
697 + 1209 Hz
1 pulse
To enter PIN protected programming
Memory 18
[2]
697 + 1336 Hz
2 pulses
Select flash duration
Memory 19
[3]
697 + 1477 Hz
3 pulses
Select dialling mode
Memory 20
[4]
770 + 1209 Hz
4 pulses
Select pause duration
Memory 21
[5]
770 + 1336 Hz
5 pulses
Key lock toggle
Memory 22
[6]
770 + 1477 Hz
6 pulses
Ringer volume
Memory 23
[7]
852 + 1209 Hz
7 pulses
Ringer melody
Memory 24
[8]
852 + 1336 Hz
8 pulses
LCD contrast
Memory 25
[9]
852 + 1477 Hz
9 pulses
Ringer on/off
Memory 26
[
]
941 + 1209 Hz
Temporary MF select
-
[#]
941 + 1477 Hz
-
-
PDF 
ZIP