Preliminary Information
MT9075B
Mode Name
BS/LS
BL/FR
JAS
JAT/JAR
Note
SysBusSync1
SysBusSync2
SysBusSync3
1
1
1
0
1
1
1
1
1
1
0
x
1
0
x
x
JA on Tx side; No JA on Rx side
JA on Rx side; No JA on Tx side
No JA on Tx or Rx side
Line
Synchronous
By default, JA is on the receive side.
Controls bits need not be selected.
Free-Run
x
0
x
x
In free-run mode JA will be automatically
disconnected
Table 2 - Selection of Clock Jitter Attenuation Modes
Depending on the mode selected, the Jitter
Attenuator (JA) can attenuate either transmit clock
jitter or receive clock jitter, or be disconnected.
Control bits JAS, JAT/JAR (address 18H of page
02H) determine the JA selection under certain
modes. Table 2 shows the configuration of related
control pins and control bits required to place the
MT9075B in the appropriate jitter attenuation mode.
clock before it has been dejittered. The
transmit data is synchronous to the clean
receive clock.
•
In Free-Run mode the transmit data is
synchronized to the internally generated
clock. The internal clock is output on pin
C4b. The clock signal extracted from the
receive data is not dejittered and is output
directly on pin E2o.
Referring to the mode names given in Table 2, the
basic operation of the jitter attenuation modes is
summarized as follows:
The PCM 30 Interface
•
In SysBusSync (1-3) modes, pins C4b and
F0b are always configured as inputs, while in
the Line Synchronous and Free-Run modes
C4b and F0b are configured as outputs.
PCM 30 (E1) basic frames are 256 bits long and are
transmitted at a frame repetition rate of 8000 Hz,
which results in an 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.
The HDB3 control bit (page 01H, address 15H, bit 5)
selects either HDB3 encoding or alternate mark
inversion (AMI) encoding. Basic frames are divided
into 32 time slots numbered 0 to 31, see Figure 31.
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.
•
In SysBusSync1 mode, an external clock is
applied to C4b. The applied clock is
dejittered by the internal PLL before being
used to transmit data. The clock extracted
(with no jitter attenuation performed) from
the receive data can be monitored on pin
E2o.
•
•
•
In SysBusSync2 mode, the clock applied to
pin C4b is assumed to be jitter-free and is
directly used to transmit data. The internal
PLL is used to dejitter the extracted receive
clock. The dejittered receive clock is output
on pin E2o.
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, ST-
BUS bit 7 is synonymous with PCM 30 bit 1; bit 6
with bit 2: and so on (Figure 31).
In SysBusSync3 mode, no jitter attenuation
is applied to either the transmit or receive
clocks. The transmit data is synchronized to
clock applied to pin C4b. The extracted
receive clock is not dejittered and is supplied
directly to the E2o output.
PCM 30 time slot 0 is reserved for basic frame
alignment, CRC-4 multiframe alignment and the
communication of maintenance information. In most
configurations time slot 16 is reserved for either
Channel Associated Signalling (CAS or ABCD bit
signalling) or Common Channel Signalling (CCS).
The remaining 30 time slots are called channels and
carry either PCM encoded voice signals or digital
In Line Synchronous mode, the clock
extracted from the receive data is dejittered
using the internal PLL and then output on pin
C4b. Pin E2o provides the extracted receive
11
MITEL [ MITEL NETWORKS CORPORATION ]
