as2507 austriamicrosystems, as2507 Datasheet - Page 3

• Manufacturer Part Number: as2507
• Description: Single Chip 2-wire Intercom Cmos Integrated Circuit
• Manufacturer: austriamicrosystems

Preliminary Data Sheet
Functional Description
The AS2507 is a CMOS integrated circuit that
incorporates a speech circuit and a FSK
modem. It is intended to be used as line-
powered interface on a 2-wire intercom bus.
Standby Condition
During standby operation (PD=High) only the
FSK demodulator is active to provide the
companion microcontroller with all signalling
information on the 2-wire bus. The low power
consumption (typical 2mA) and a high input
and output impedance in standby mode allow
the parallel operation of many terminals on
each bus pair.
2/4-Wire Conversion
The
cancellation circuit. The transmit signal is
attenuated by 6 dB over the 600
impedance) and subtracted from the receive
signal
configuration allows the selection of the
required ac impedance and yet maintaining a
good side tone cancellation.
AC Impedance
The ac impedance is determined by an
external resistor at the TO output (typical
600 ).
Transmit Path
The gain of the transmit path from the
microphone inputs (M1/M2) to the transmit
output (TO) is set to 32 dB. The soft clip level
is set to 0.5V
impedance is 60k .
Receive Path
The gain of the receive path from the receive
input (RI) to the receive output (RO) is set to
-6dB. The receive input is internally biased to
A
GND
with a 500k
AS2507
at
the
PEAK
has
at TO. In standby the output
receive
resistor.
a
built-in
input
resistor (ac
(RI).
side
tone
This
3/9
FSK Modulator
Two signalling modes are provided, namely
FSK and burst mode. The signalling mode and
the
microcontroller using the TE and TXD inputs
as follows:
FSK Demodulator
Also the demodulator provides two modes for
detection as follows:
Signal on line
IDLE, no transmission
SPACE ("0") 18.645 kHz
MARK ("1") 22.375 kHz
The demodulator consists out of a bandpass
filter to attenuate interfering speech signals
and a period counter. The RxD output is
updated after each valid period or a counter
overflow.
Transmission Protocol
In order to assure a safe data transmission,
data framing is recommended. Each frame
should consist out of a preamble (e.g. FF
a header (e.g. AA
checksum.
Independence of bus polarity
Centrally supplied terminals can be connected
to the 2-wire bus independent from polarity. In
this case a rectifier bridge, known from
telephony, is recommended since the DC-
supply current will bias the diodes.
TE
0
0
1
1
signalling
TXD
0
1
0
1
MODE
IDLE, no transmission
TEST, for testing only
SPACE ("0") 18.645 kHz
MARK ("1") 22.375 kHz
can
hex
be
), data bytes and
RXD
controlled
1
0
1
July 1998
AS2507
by
hex
a
),