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Data Sheet AS2540
austriamicrosystems
austriamicrosystems
DATA SHEET (PRELIMINARY)
Remote Controlled Single-Chip-Telephone
AS2540
General Description
The AS2540 is a CMOS integrated circuit that
incorporates a speech circuit (line-adaptation, 2/4-wire
conversion, separate Rx- and Tx-amplifiers for handset
and modem), MF dialler, ring frequency detector, ring
melody generator and a two wire serial interface. It
shall act as an a/b-line-powered device in order to
interface a main-powered CPU to the analogue
telephone line.
AS2540 can operate in a so-called mainpower mode
and in a backup mode. During mainpower mode, a
watchdog timer is running on AS2540, which has to be
reset via the serial interface, which is connected to the
CPU through opto-couplers. During backup mode (=
The main-power failure or SW engine problem),
AS2540 can operate as an independent basic MF
dialler (digits 0-9*#)
Key Features
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Applications
-
-
-
-
-
Web Telephones
Answering Machines
Fax Machines
Base Station of Cordless Telephones
Hospital Communication Units
Block Diagram
Line
ch
ni
c
SMUT
E
S
MASK
S
MAS
K
SMUTE
SROH
SROH
SROT
S
DPn
S
DPn
Dia l
Dig it
Dial
Digit
Te
ST
IT
SROT
ST
IT
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Package
-
-
Line Interface, Speech Circuit, MF Dialler and Tone Ringer
on a 28 pin CMOS chip
Programmable via 2-wire serial interface
(UART 9600 baud, 8N1)
Watch dog timer for Backup Mode
Additional input for modem transmit path
Additional output for modem receive path
CMOS for high EMC immunity
Low Noise (max. –72 dBm)
Operating range from 15mA to 100mA (down to 5mA with
reduced performance)
Soft clipping for handset operation to avoid harsh distortion
Line loss compensation selectable by pin option
Real and complex impedance selectable by external
components
Side tone adaption selectable by external components
Ring frequency discrimination
3-tone ring melody generator
28 pin SOIC
Dice-on-Foil
Main Power Mode
+ 6dB
Backup Mode
LS
LI
Line
LS
LI
+ 6dB
RI
SB
T
-2d B
ROH
+ 2d B
ROT
M1
M2
T
IT
RI
SB
T
-2dB
+ 2d B
CS
CS
Mask
Mask
CI
CI
AGND
DPn
DT
MF-
g enerator
DPn
DT
MF-
generator
RxD
DIALLER
C1
C2
C3
R1
R2
MODE
UART
T
xD
C1
C2
C3
R1
R2
MODE
VDD
DIALLER
UART
RFD
MO
EHS
MHS
VS
S
OSC
RFD
MO
EHS
MHS
VS
S
OS
C
al
id
ROH
ROT
M1
M2
T
IT
AGND
RxD
T
xD
VDD
Page 1 of 18
Data Sheet AS2540
austriamicrosystems
Pin Description
Pin #
15
Symbol
RFD
Function
R
ing
F
requency
D
iscrimination
Schmitt trigger input for ring frequency discrimination. Disabled during off-hook.
7
LS
L
ine Current
S
ense Input
L
ine
I
nput
Input used for power extraction and line current sensing
5
LI
6
RI
R
eceive
I
nput
Input for ac-separated receive signal
2
STB
S
ide
T
one
B
alance Input
Input for side tone cancellation network
3
CS
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
8
CI
C
omplex
I
mpedance Input
D
ial
P
ulse Output
Input pin for the capacitor to program a complex impedance
16
DPn
Open drain output pulls low during break periods of pulse dialling and flash
17
EHS
E
lectronic
H
ook
S
witch
M
anual
H
ook
S
witch
Schmitt Trigger Input to detect an electronic off-hook.
18
MHS
Schmitt Trigger Input to detect a manual off-hook.
19
MODE
D
TMF
L
evel
S
election
-4/-6dBm
-6/-8dBm
-8/-10dBm
ch
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L
ine
L
oss
C
ompensation Select Pin
45mA-75mA
20mA-50mA
None
Ring
—>
—>
—>
LLC open
LLC-r3
LLC-r4
28
MO
Te
PDM output of the ring melody generator.
11
VDD
V
oltage
D
rain
D
rain
Positive Power Supply
4
VSS
V
oltage
S
ource
S
ource
Negative Power Supply
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—>
—>
—>
DLS open
DLS-r1
DLS-r2
M
elody
O
utput
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Input for sensing the line current
Data Sheet AS2540
austriamicrosystems
Pin #
25
Symbol
OSC
Function
O
scillator Input
Input for ceramic resonator 3.58MHz.
Recommended type: Murata CSA 3.58MG312AM or compatible
12
AGND
A
nalogue
G
round
Special ground for the internal amplifiers
Schmitt trigger input to serial interface
27
TXD
T
ransmit
D
ata Output
Open drain output from serial interface
Keyboard
Keyboard
20
21
22
23
24
10
R1
R2
C1
C2
C3
ROT
R
eceive
O
utput to
T
ransformer
Output for driving a transformer with an ac impedance larger than 10kΩ
1
TIT
T
ransformer
I
nput from
T
ransformer
Single ended input for transformer
9
ROH
R
eceive
O
utput to
H
andset
M
icrophone Inputs
Output for driving a dynamic earpiece with an impedance from 150Ω to 300Ω
13
14
M2
M1
Differential inputs for the microphone (electret)
Te
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ows
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olumns
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26
RXD
R
eceive
D
ata Input
Data Sheet AS2540
austriamicrosystems
Functional Description
Modes of operation
There are 4 possible modes:
Example Main Power Mode
Line
LS
LI
+ 6dB
RI
ST
B
-2dB
+ 2dB
ROH
ROT
M1
M2
Idle Mode
Manual hook-switch and electronic hook-switch (e.g. relay)
is open (MHS
∩
EHS = logical 0), no ring signal is applied,
the oscillator is stopped, signalling via the serial interface
is not possible.
CS
Mask
T
IT
CI
DP
n
DT
MF-
generator
AS2540 is supplied via the ring capacitor and external
path, manual hook -switch and electronic hook-switch is
open (MHS
∩
EHS = logical 0), the oscillator is running, a
valid incoming ringing is signalled via the serial interface to
the CPU. If the CPU does not reply the AS2540 switches
into backup mode and sends a ring melody to the MO
output.
Backup Mode
Manual hook-switch and/or electronic hook-switch is closed
(MHS
∪
EHS = logical 1), AS2540 is supplied with line
current, the oscillator is running, the keyscan is enabled
and the handset path is switched on, signalling via the
serial interface is possible. After AS2540 has started
dialling in backup mode, he must not be interrupted any
more in order to ensure consistent dialling. A mode
transition BM -> MPM is only possible before AS2540 has
started dialling digits independently.
Main Power Mode
Manual hook-switch and/or electronic hook-switch is
Select Operation Mode
ch
ni
c
closed, AS2540 is supplied with line current (MHS
∪
EHS
= logical 1), the oscillator is running, the keyscan is
disabled, AS2540 is controlled via the serial interface,
handset path or monitor path or modem path is on,
signalling via the serial interface is possible.
Te
Command Message
<SetHandsetPath>
<SetModemPath>
<SetMonitorPath>
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DIALLER
UART
T
xD
C1
C2
C3
R1
R2
MODE
RFD
VDD
VS
S
MO
EHS
OS
C
MHS
Ringing Mode
Start-up in backup mode
As soon as AS2540 is supplied with line current, the
external V
dd
capacitor will be charged up via the LI and
VDD pin and after the V
dd
voltage has reached the
operating level, the handset path of the speech circuit is
switched on. This off-hook status is also signalled to the
internal logic via the MHS or EHS pin in order to start the
pinscan and subsequently set the country specific modes.
Additionally a <LineEvent> message is sent to the CPU.
Start-up in ring mode
Switches ON
SROH
SROT & STIT
SROH & SROT
Switches OFF
SROT & STIT
STIT
When a ringing signal is applied to the line, V
dd
of AS2540
is charged up via an external path. After V
dd
has reached
the operating voltage the oscillator starts and AS2540
discriminates the ring frequency. After a valid ring
frequency is applied on the RFD pin, the logic sends a
<LineEvent> message is sent to the CPU and a watchdog
timer is started. When the <LineEvent> message is not quit
by the CPU before the watchdog timer has finished the
countdown, AS2540 changes into backup mode and sends
out a melody via the MO pin.
DC conditions
The normal operating mode is from 15mA to 100mA. An
operating mode with reduced performance is from 5mA to
15mA. In the line hold range from 0mA to 5mA the device
is in a power down mode and the voltage at LI is reduced
to a maximum of 3.5V
al
id
AGND
SROT
S
MAS
K
SMUT
E
S
DPn
Dial
Digit
SROH
ST
IT
RxD
Page 4 of 18
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