Preliminary Information
Pin Description (Continued)
Pin #
14
15
16
17
18
19
20
Name
TLA
TLB
NC
NC
NC
TXA
TXB
Description
MH89792
Transmit Line B (Output).
The B wire of Ring connection of the E1 receive line should be
connected to this pin.
Transmit Line B (Output).
The B wire or Tip connection of the E1 receive line should be
connected to this pin.
No Connection.
This pin is not fitted.
No Connection.
This pin is not fitted.
No Connection.
This pin is not fitted.
Transmit A (Input).
A unipolar signal from the framer device used in conjunction with TxB
is used to generate the bipolar output signal.
Transmit B (Input).
A unipolar signal from the framer device used in conjunction with TxA
is used to generate the bipolar output signal.
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 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.
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”
Af (dB) = AF
ref
(dB)*
√f
f
ref
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).
Where:
AF - attenuation at frequency f in dB
AF
ref
- attenuation at frequency f
ref
in dB (in kHz)
f
ref
- reference frequency (in this case 1024) kHz
f - frequency in kHz
4-225
MITEL [ MITEL NETWORKS CORPORATION ]
