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3465&3485-mfc.ib.rev4.doc
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17/10/2007
Technical description
The MFC-3485 and MFC-3465 form a system for encoding and decoding the data in an ASI data stream for
transport in a G.703 stream. The MFC-3485 takes ASI data rates from 1.5 to 30 Mb/s and adds stuffing bytes to
convert the signal to run on a 34 Mb/s (E-3) G.703 system (MFC-3485/34, 34 Mb/s version) or ASI data rates from
1.5 to 39 Mb/s and adds stuffing bytes to convert the signal to run on a 45 Mb/s (DS-3) G.703 system (MFC-
3485/45, 45 Mb/s version). The MFC-3465 decodes and removes the stuffing bytes to restore the original ASI data
steam.
As the MFC-3485 does the original encoding, it will be described in detail first.
MFC-3485
ASI Input
The input ASI signal passes through an automatic line equalisation circuit, U1. The purpose of this equaliser is to
restore both the signal level and the leading and trailing edges of the digital signal so that signal jitter is reduced
prior to feeding the next stage, U2, which is a serial to parallel data converter which feeds the main logic processor,
U5.
Logic processing, reclocking and error detection.
The main logic processing, reclocking, error detection and operational interfacing are all performed by logic circuits
within a custom programmed large scale logic array. The internal logic and functions of this IC are too complex to
describe in detail and the following is intended as a guide to function only. Data rates are byte stuffed here to bring
the rate up to standard G.703 rates depending on the version of card, i.e. 34 Mb or 45 Mb.
Data loss detection.
Receipt of an invalid ASI byte is considered a loss of data.
Sync Error
ASI packet sync has been lost at the output of the FIFO.
188 TS Sync length indicator
If the number of bytes between TS packet syncs is 188 then the 188 LED lights. When either a loss of input or sync
loss is detected, this LED is extinguished.
204 TS Sync length indicator
If the number of bytes between TS packet syncs is 204 then the 204 LED lights. When either a loss of input or sync
loss is detected, this LED is extinguished.
Alarm relay
An alarm output is available on the rear assembly using a two pin connector.
The relay contact will short circuit the two pins on the rear assembly when the selected alarm condition occurs,
selectable by link LK3 (see configuration section) or there is a loss of power to the module.
G.703 Output
U4 is a G.703 data driver IC feeding a transformer to give an output on the rear connector unit. Link settings set the
output for either HDB3 for the 34 Mb version or B3ZS for the 45 Mb (link LK1) and whether the output is shaped
or unshaped (link LK2). See configuration section for settings.
SPI Output
True SPI output is also provided on rear connector unit.