Preliminary Information

MH89792

4-225

14

TLA

Transmit Line B (Output). The B wire of Ring connection of the E1 receive line should be

connected to this pin.

15

TLB

Transmit Line B (Output). The B wire or Tip connection of the E1 receive line should be

connected to this pin.

16

NC

No Connection. This pin is not fitted.

17

NC

No Connection. This pin is not fitted.

18

NC

No Connection. This pin is not fitted.

19

TXA

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

is used to generate the bipolar output signal.

20

TXB

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

is used to generate the bipolar output signal.

Pin Description (Continued)

Pin #

Name

Description

Functional Description

The MH89792 is a 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

receive

circuitry,

inductorless

clock

recovery, data and clock polarity selection and loss

of signal indication.

Bipolar Line Receiver

The MH89792 receiver interfaces to the transmission

line through an internal pulse transformer which

splits the received AMI lines signal into RxA and

RxB. These two signals are combined by internal

logic to form a new signal which represents the

received data, RxD. The signals RxA and RxB may

be inverted where required by applying a logic low

signal permanently to pin 7, (RxINV). RxD will not be

affected by use of this pin.

The input impedance seen by the transmission line is

about 120 ohms when using the -1 variant for twisted

pair applications, about 75 ohms when using the -2

variant for coaxial cable applications, and is about

100 ohms when using the -3 variant for digital

twisted pair applications.

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

MH89792

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 MH89792 contains a clock extraction circuit

which 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 and

can be configured as either rising or falling edge by

the use of pin 8. (CLKF/CLKR).

Loss of Signal

The circuitry on the MH89792 is capable of detecting

128 continuous ZEROs received on RLA and RLB

and indicating this condition as a logic low on pin 9,

(LOS). When LOS and RxINV are low RxA and RxB

are forced high, when LOS is low and RxINV is high

RxA and RxB are forced low LOS will not reset until

64 ONEs are received in a two E1 frame period. LOS

may be inverted by applying a logic low to pin 10,

(LOSP).