MH89770
Preliminary Information
With both the T1 data and the CEPT data converted
to the ST-BUS format, the two digital trunks can
exchange information through the switch matrix.
Unfortunately, the signalling information from the two
formats is not exchanged as easily. The T1 A and B
signalling bits must be read by the controlling
microprocessor and converted in software to the
CEPT ABCD signalling bits, and vice versa. The
circuit must also convert all the channels carrying
voice data to the appropriate encoding scheme, (i.e.,
T1 µ-Law or CEPT A-Law). This is done by the block
labelled DSP in Figure 18, Digital Signal Processor.
Packaging
The MH89770 is available in two package options
which are:
•
•
The MH89770S which is a surface mountable
version of the MH89770N is suitable for
Infrared Reflow (I.R.) soldering. See Figure 35
for the dimensional drawing, and Figure 36 for
the recommended footprint.
The MH89770N has a row pitch of 0.8”. See
Figure 37 for the dimensional drawing for this
part.
The final component of the system is the MT8941.
The extracted 8 kHz outputs from the T1 and the
CEPT interfaces are combined with an AND gate
before being connected to the MT8941. One of the
interfaces is selected as the synchronization source
by enabling its output through the Master Control
Word of the chosen interface. Phase-locked loop #2
will then generate ST-BUS clocks that are
synchronized to either the T1 network or the CEPT
network. Phase-locked loop #1 is configured to
generate the T1 transmit clock synchronized to the
ST-BUS. Therefore, if the ST-BUS is synchronized to
one network then the elastic buffer in the opposite
interfaces will perform controlled slips between that
network and the T1 to CEPT converter.
Magnetics Information
For supporting initial design activities, Mitel
Semiconductor has available the MH89770 Magnetic
Kit which contains the magnetics shown in Figure 11.
Alternatively, they are available directly from the
following manufacturer:
Filtran Ltd.
229 Colonnade Road
Nepean, Ontario
Canada K2E 7K3
Telephone: (613) 226-1626
Please refer to Figure 6 for the transformer part
numbers.
4-150
MITEL [ MITEL NETWORKS CORPORATION ]
