MT8977 Mitel Networks Corporation, MT8977 Datasheet - Page 7

• Manufacturer Part Number: MT8977
• Description: ISO-CMOS ST-BUS FAMILY T1/ESF Framer Circuit
• Manufacturer: Mitel Networks Corporation

to the CRC received in the next multiframe.
device will not declare itself to be in synchro nization
unless a valid framing pattern in the S-bit is detected
and a correct CRC is received. The CRC check in
this case provides protection against false framing.
The CRC check can be turned off by setting bit 1 in
Master Control Word 2.
The device can be forced to resynchronize itself. If
Bit 3 in Master Control Word 2 is set for one frame
and then subsequently reset, the device will start to
search for a new frame position.
reframe is made by the user’s system processor on
the basis of the status conditions detected in the
received master status words.
consideration of the number of errors in the received
CRC in conjunction with an indication of the presence
of a mimic. When the device attains synchronization
the mimic bit in Master Status Word 1 is set if the
device found another possible candidate when it was
searching for the framing pattern.
Note that the device will resynchronize automatically
if the errors in the terminal framing pattern (F
FPS) exceed the threshold set with bit 0 in Master
Control Word 2.
Standard D3/D4 framing is enabled when bit 4 of
Master Control Word 2 is reset (logic 0).
mode the device searches for and inserts the
framing pattern shown in Table 4. This mode only
supports AB bit signalling, and does not contain a
CRC check.
Preliminary Information
Bit
7
6
5
4
3
2
1
0
Robbed bit
Debounce
ESFYLW
TSPZCS
8KHSel
YLALR
Name
B8ZS
XCtl
When set the received A, B, C and D signalling bits are reported directly in the per channel status
words output at CSTo. When clear, the signalling bits are debounced for 6 to 9 ms before they are
placed on CSTo.
Transparent Zero Code Suppression. When this bit is set, no zero code suppression is
implemented.
Binary Eight Zero Suppression. When this bit is set, B8ZS zero code suppression is enabled.
When clear, bit 7 in data channels containing all zeros is forced high before being transmitted on the
DS1 side. This bit is inactive if the TSPZCS bit is set.
8 kHz Output Select. When set, the E8Ko pin is held high. When clear, the E8Ko generates an 8
kHz output derived from the E1.5i or C1.5 clock (see Pin Description for E8Ko).
External Control Pin. When set, the XCtl pin is held high. When clear, XCtl is held low.
ESF Yellow Alarm. Valid only in ESF mode. When set, a sequence of eight 1’s followed by eight 0’s
is sent in the FDL bit positions. When clear, the FDL bit contains data input at the TxFDL pin.
When this bit is set, robbed bit signalling is disabled on all DS0 transmit channels. When clear, A, B,
C and D signalling bit insertion in bit 8 for all DS0 transmit channels in every 6
Yellow Alarm. When set, bit 2 of all DS1 channels is set low. When clear, bit 2 operates normally.
Table 1. Master Control Word 1 (Channel 15, CSTi0)
This may include
The decision to
In this
T
The
or
The CRC/MIMIC bit in Master Control Word 2, when
set high, allows the device to synchronize in the
presence of a mimic. If this bit is reset, the device
will not synchronize in the presence of a mimic (Also,
refer to section on Framing algorithm).
In the D3/D4 mode the device can also be made
compatible with SLC-96 by setting bit two of Master
Control Word 2. This allows the user to insert and
extract the signalling framing pattern on the DS1 bit
stream using the FDL input and output pins. The user
must format this 4 kbits of information externally to
meet all of the requirements of the SLC-96
specification (see Table 5). The device multiplexes
and demultiplexes this information into the proper
position. This mode of operation can also be used for
any other application that uses all or part of the
signalling framing pattern.
stream clocked into the TxFDL contains two proper
sets of consecutive synchronization bits (as shown in
Table 5 for frames 1 to 24), the device will be able to
insert and extract the A, B signalling bits. The TxSF
pin should be held high in this mode. Superframe
boundaries cannot be defined by a
input.
indicates the superframe boundaries based on the
synchronization pattern in the F
position.
Zero Code Suppression
The combination of bits 5 and 6 in Master Control
Word 1 allow one of three zero code suppression
schemes to be selected. The three choices are:
none, binary 8 zero suppression (B8ZS), or jammed
bit (bit 7 forced high). No zero code suppression
Description
The RxSF output functions normally and
ISO-CMOS
As long as the serial
th
frame is enabled.
S
MT8977
pulse on this
received bit
4-105
.