MT9079
A new feature is the ability to select transparent or
termination modes of operation. In termination mode
the CRC-4 calculation is performed as part of the
framing algorithm. In transparent mode the MT9079
allows the data link maintenance channel to be
modified and updates the CRC-4 remainder bits to
reflect this new data. All channel, framing and
signalling data passes through the device unaltered.
This is useful for intermediate point applications of
an PCM 30 link where the data link data is modified,
but the error information transported by the CRC-4
bits must be passed to the terminating end. See the
Application section of this data sheet.
Functional Description
The MT9079 is an advanced PCM 30 framer that
meets
or
supports
the
layer
1
CCITT
Recommendations of G.703, G.704, G.706, G.775,
G.796 and G.732 for PCM 30; I.431 for ISDN
Primary Rate; and T1.102 for DS1A. It also meets or
supports the layer 1 requirements of ETSI ETS 300
011 and ETS 300 233. Included are all the features
of the MT8979, except for the digital attenuation
ROM and Alternate Digit Inversion (ADI). It also
provides extensive performance monitoring data
collection features.
The MT9079 has a comprehensive suite of status,
alarm, performance monitoring and reporting
features. These include counters for BPVs, CRC
errors, E-bit errors, errored frame alignment signals,
BERT, and RAI and continuous CRC errors. Also,
included are transmission error insertion for BPVs,
CRC-4 errors, frame and non-frame alignment signal
errors, and loss of signal errors.
Control of the MT9079 is achieved through the
hardware
selection
of
either
a
parallel
non-multiplexed microprocessor port, an Intel or
Motorola serial controller port, or an ST-BUS port.
The parallel port is based on the signals used by
Motorola microprocessors, but it can also be easily
mated to Intel microprocessors (see the Applications
section of this data sheet).
Dual transmit and receive 16 byte circular buffers, as
well as line code insertion and detection features
have been implemented and can be associated with
any PCM 30 time slot.
The serial microcontroller interface of the MT9079
will automatically adapt to either Intel or Motorola
signalling. An ST-BUS interface, consisting of two
control and one status stream, may also be selected,
however, the circular and national bit buffers cannot
be accessed in this mode.
A complete set of loopbacks has been implemented,
which include digital, remote, ST-BUS, payload, and
local and remote time slot.
The MT9079 supports enhanced features of the
MT8979. The receive slip buffer hysteresis has been
extended to 26 channels, which is suitable for
multiple trunk applications where large amounts of
wander tolerance is required. The phase status word
has been extended to the one sixteenth bit when the
device is clocked with C4. This provides the
resolution required for high performance phase
locked loops such as those described in MSAN-134.
The functionality of the MT9079 has been heighten
with the addition of a comprehensive set of maskable
interrupts and an interrupt vector function. Interrupt
sources consist of synchronization status, alarm
status, counter indication and overflow, timer status,
slip indication, maintenance functions and receive
channel associated signalling bit changes.
The received CAS (Channel Associated Signalling)
bits are frozen when signalling multiframe
synchronization is lost, and the CAS debounce
duration has been extended to be compliant with
CCITT Q.422.
The PCM 30 Interface
PCM 30 (E1) basic frames are 256 bits long and are
transmitted at a frame repetition rate of 8000 Hz,
which results in a aggregate bit rate of 256 bits x
8000/sec.= 2.048 Mbits/sec. The actual bit rate is
2.048 Mbits/sec +/- 50 ppm encoded in HDB3
format. Basic frames are divided into 32 time slots
numbered 0 to 31, see Figure 32. Each time slot is 8
bits in length and is transmitted most significant bit
first (numbered bit 1). This results in a single time
slot data rate of 8 bits x 8000/sec. = 64 kbits/sec.
The MT9079 framing algorithm has been enhanced
to allow automatic interworking between CRC-4 and
non-CRC-4 interfaces. Automatic basic frame alarm
and multiframe alarms have also been added.
The national bits of the MT9079 can be accessed in
three ways. First, through single byte registers;
second, through five byte transmit and receive
national bit buffers; and third, through the data link
pins TxDL, RxDL and DLCLK.
It should be noted that the Mitel ST-BUS also has 32
channels numbered 0 to 31, but the most significant
bit of an eight bit channel is numbered bit 7 (see
Mitel Application Note MSAN-126). Therefore,
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MITEL [ MITEL NETWORKS CORPORATION ]
