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Preliminary Information

MH89793

16

TXB

Transmit B (Input). A unipolar signal from the framer device used in conjunction with TXA

is used to generate the bipolar output signal.

17

NC

No Connection. This pin is used for internal connection.

18

NC

No Connection. This pin is used for internal connection.

19

NC

No Connection. This pin is used for internal connection.

20

VDD

D.C. Power (Input). +5V supply.

21

E2o

2048kHz Extraction Clock (Output). This clock is extracted by the device from the

received signal. It is used internally to clock in data received from RLA and RLB.

22

RXB

Receive B (Output). This pin is connected to the negative receive pin of the framer and

provides a signal of the same format as RXA.

23

RXA

Receiver A (Output). The bipolar CEPT signal received by the device at RLA and RLB

input is converted to a unipolar format and output at this pin. This pin is connected to the

positive receive pin of the framer.

24

VSS

Ground (Input). D.C. power return path.

25

LOS

Loss of Signal (Output). This pin goes low when 128 contiguous zeros are received on

the RLA and RLB inputs. LOS is reset when 64 ones are received in dual E1 frame periods.

26

NC

No Connection. This pin is used for internal connection.

27

RZA

Receive Impedance Select. This pin is connected to pin 17 RZB to select 75

Ω input

impedance. For 120

Ω operation this pin is left open circuit.

28

RZB

Receive Impedance Select. This pin is connected to pin 16 RZA to select 75

Ω input

impedance. For 120

Ω operation this pin is left open circuit.

Pin Description (Continued)

Pin #

Name

Description

Functional Description

The MH89793 is an E1 digital trunk interface which

when used with an approved framer will conform to

CCITT recommendation G.703 for PCM30 and I.431

for the ISDN. The functions provided include line

driver

and

receiver circuitry, inductorless

clock

recovery, and loss of signal indication.

Bipolar Line Receiver

The MH89793 receiver interfaces to the transmission

line through an internal pulse transformer which

splits the received AMI lines signal into RxA and

RxB. The line impedance is selected by linking

appropriate option pins.

Attenuation of the transmission line shall not exceed

6dB (at 1024kHz) and attenuation characteristics

shall be close to the “square root of f”.

√f

Where:

AF - attenuation at frequency f in dB

f - frequency in kHz

Bipolar Line Transmitter

The

MH89793

transmitter

interfaces

to

the

transmission

line

through

an

internal

pulse

transformer which combines the TxA and TxB data

into an AMI line coded signal. This is then passed

through the 6dB pad prior to being applied to the

line.

Clock Extractor

The MH89793 contains a clock extraction circuit that

generates the E2o clock from the received data

without the use of external crystals or a tunable

inductor.

The edge of the E2o extracted clock approximately

aligns with the centre of the received data pulse.