MT8977 Mitel Networks Corporation, MT8977 Datasheet - Page 12

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

MT8977
The elastic buffer in the MT8977 permits the device
to handle 26 ST-BUS channels or 156 UI of jitter/
wander (see description of elastic buffer in the next
section). In order to prevent slips from occurring, the
frequency corrections would have to be implemented
such that the deviation in the phase status word is
limited to 26 channels peak-to-peak. It is possible to
use a more sophisticated protocol, which would
center
4-110
Bit
Bit
4-3
2-0
Bit
7-4
Bit
7-3
2-0
7
6
5
4
3
2
1
0
7
6
5
3
2
1
0
the
ChannelCnt
ESFYLW
MFSYNC
CRCCNT
BPVCnt
YLALR
Unused
Name
MIMIC
Name
BlAlm
Name
FrCnt
SLIP
ERR
BPV
SYN
Name
BitCnt
XSt
A
B
C
D
elastic
ISO-CMOS
buffer
Yellow Alarm Indication. This bit is set when the chip is receiving a 0 in bit position 2 of every
DS0 channel.
This bit is set if the frame search algorithm found more than one possible frame candidate when it
went into frame synchronization.
Terminal Framing Bit Error. The state of this bit changes every time the chip detects 4 errors in
the F
ESF Yellow Alarm. This bit is set when the device has observed a sequence of eight one’s and
eight 0’s in the FDL bit positions.
Multiframe Synchronization. This bit is cleared when D3/D4 multiframe synchronization has
been achieved. Applicable only in D3/D4 and SLC-96 modes.
Bipolar Violation Count. The state of this bit changes every time the device counts 256 bipolar
violations.
Slip Indication. This bit changes state every time the elastic buffer in the device performs a
controlled slip.
Synchronization. This bit is set when the device has not achieved synchronization. The bit is
clear when the device has synchronized to the received DS1 data stream.
Blue Alarm. This bit is set if the receiver has detected two frames of 1’s and an out of frame
condition. It is reset by any 250 microsecond interval that contains a zero.
Frame Count. This is the ninth and most significant bit of the “Phase Status Word“ (see Table
10). If the phase status word is incrementing, this bit will toggle when the phase reading exceeds
channel 31, bit 7. If the phase word is decrementing, then this bit will toggle when the reading
goes below channel 0, bit 0.
External Status. This bit reflects the state of the external status pin (XSt). The state of the XSt
pin is sampled once per frame.
Bipolar Violation Count. These two bits change state every 128 and every 64 bipolar violations,
respectively.
CRC Error Count. These three bits count received CRC errors. The counter will reset to zero
when it reaches terminal count. Valid only in ESF mode.
Unused Bits. Will be output as 0’s.
These are the 4 signalling bits as extracted from the received DS1 bit stream.
The bits are debounced for 6 to 9 ms if the debounce feature is enabled via bit 7 in Master Control
Word 1.
Channel Count. These five bits indicate the ST-BUS channel count between the ST-BUS frame
pulse and the rising edge of E8Ko.
Bit Count. These three bits provide one bit resolution within the channel count described above.
Table 11. Per Channel Status Word Output on CSTo
Table 8. Master Status Word 1 (Channel 15, CSTo)
Table 9. Master Status Word 2 (Channel 31, CSTo)
T
Table 10. Phase Status Word (Channel 3, CSTo)
or FPS bit pattern. The bit will not change state more than once every 96ms.
and
permit
more
jitter/wander to be handled.
applications, including ACCUNET
the 156 UI of jitter/wander tolerance is acceptable.
Description
Description
Description
Description
Preliminary Information
However, for most
®
T1.5 (138 UI),