MT88E39
Pin Description
Pin #
12
Name
CD
Description
Data Sheet
Carrier Detect (Open Drain/CMOS Output).
Active low. In mode 0 (MT88E41 compatible
mode - when the MODE pin is logic low) this is an open drain output. In mode 1 (when the
MODE pin is logic high) this is a CMOS output.
A logic low indicates that a carrier has been present for a specified time on the line. A time
hysteresis is provided to allow for momentary discontinuity of carrier. The demodulated FSK
data is inhibited until the carrier has been detected.
13
14
PWDN
Power Down (Schmitt Input).
Active high. Powers down the device including the input op-
amp and the oscillator. Must be low for operation.
MODE
Mode select (Input).
This pin selects the 3-wire FSK interface mode. To select mode 0
(MT88E41 compatible mode) this pin should be logic low. To select mode 1 this pin should be
logic high.
Because this pin is already connected to Vss in ’E41 applications, the MT88E39 can replace
the ’E41 without any circuit or software change.
IC
V
DD
Internal Connection.
Internal connection. Leave open circuit. In MT88E41, this was IC2
which was also left open in the application circuit.
Positive power supply voltage.
15
16
Functional Description
The MT88E39 is a FSK demodulator compatible with FSK based Caller ID services around the world, such as in
North America, France, Germany, and Japan. Caller ID is the generic term for a group of services offered by
telephone operating companies whereby information about the calling party is delivered to the subscriber. In the
FSK based methods, the information is modulated in either Bell 202 (in North America) or CCITT V.23 (in Europe)
FSK format and transmitted at 1200 baud from the serving end office to the subscriber’s terminal.
In North America, Caller ID uses the voiceband data transmission interface defined in the Bellcore document GR-
30-CORE. The terminal or CPE (Customer Premises Equipment) requirements are defined in Bellcore document
SR-TSV-002476. Typical services are CND (Calling Number Delivery), CNAM (Calling Name Delivery), VMWI
(Visual Message Waiting Indicator) and CIDCW (Calling Identity Delivery on Call Waiting).
In on-hook Caller ID, such as CND and CNAM, the information is typically transmitted from the end office before the
subscriber picks up the phone. There are various methods such as between the first and second rings (North
America), between an abbreviated ring and the first true ring (Japan, France and Germany). On-hook Caller ID can
also occur without ringing for services such as VMWI. The MT88E39 is suitable for these forms of alerting.
In off-hook Caller ID, such as CIDCW, information about a new calling party is sent to the subscriber who is already
engaged in a call. Bellcore’s method uses a special dual tone known as CAS (CPE Alerting Signal) which should be
detected by the CPE. After the CPE has acknowledged with a DTMF digit, the end office will send the FSK data.
The MT88E39 is suitable for receiving the FSK data but a separate CAS detector is required.
The MT88E39 provides an interface to the Caller ID physical layer. It bandpass filters and demodulates the 1200
baud FSK signal. It also provides a convenient interface to extract the demodulated FSK data. Although the main
application of the MT88E39 is Caller ID, it can also be used wherever 1200 baud Bell 202 and/or CCITT V.23 FSK
reception is required.
3 to 5V operation
The MT88E39 can operate from 5.5 V down to 2.7 V, but the FSK reject level will change with Vdd. In a battery
powered CPE, the FSK accept level will become lower as the batteries are run down. If the CPE is designed for
4.5 V, the accept level will be lowered when the batteries drain to 3 V. In North America there is a requirement for
rejecting FSK signals which are below 3 mVrms when data is not preceded by ringing, such as VMWI (Visual
3
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