MT8926AE Zarlink Semiconductor, MT8926AE Datasheet - Page 10

• Manufacturer Part Number: MT8926AE
• Description: MT8926 - T1 Performance Monitoring Adjunct Circuit (PMAC)
• Manufacturer: Zarlink Semiconductor

1.4
The PMAC will decode the bit-oriented priority codeword 11111111 00000000 received on the FDL as a Remote
Alarm Indication (RAI or Yellow Alarm) signal as per T1.403/408. See the section on MT8926 FDL message transfer.
This 16 bit pattern must be detected in seven out of 10 codewords in order for the RAI bit of Master Status Word 1
(CSTo channel 15 bit 4) to go high (see Table 3 on page 9). If more than three out of 10 codewords are in error, then
RAI will remain low.
A low to high transition of the RAI bit will initiate a group one (G1) interrupt. See the section on interrupts for the
control of the RAI interrupt.
1.5
The LOS bit of Master Status Word 1, Table 3 on page 9, will be high if the MT8926 receives 128 or more
consecutive zeros from the T1 interface. LOS will return low when a ones density of 12.5% has been achieved
(approximately 48 ones is received in two or less frames).
1.6
The payload of a T1 signal consists of the 192 data bits of each frame and excludes the framing bit (the first bit of
193). Therefore, a T1.403 or T1.408 ESF payload loopback extracts the payload of a receive T1 signal and transmits
it back to the originator with new framing bits. This allows the transport of maintenance and performance data over
the facility data link while the payload loopback is activated. The CRC-6 multiframe alignment remainder will not be
looped around, but will function normally (i.e., calculated for each direction of transmission).
The MT8926 PMAC can perform a payload loopback by muxing the data received on the MT8976/77’s DSTo to DSTi
of the MT8976/77. This is controlled by the MT8926 Loopback Control Word (CSTi1 channel 15, see Table 4 on
page 9).
Figure 6 on page 8 illustrates the MT8926 payload loopback connections. The ST-BUS transmit stream (normally
connected to DSTi of the MT8976/77) will connect to DSTi0 of the MT8926. The DSTo stream of the MT8976/77 will
connect to DSTi1 of the MT8926 and to the ST-BUS receive stream. DSTo of the MT8926 will connect to DSTi of
the MT8976/77.
MT8926
10
7-5
Bit
4
3
Remote Alarm Indication (RAI)
Loss of Signal Indication (LOS)
Payload Loopback
Name
LLDD
LLED
---
Table 5 - PMAC Miscellaneous Status Word (CSTo Channel 7)
Not Used.
Line Loopback Disable Detect. This bit is set when a repeating 001 pattern (either
framed or unframed) is detected in the received T1 signal for at least five frames.
In order to comply with T1.403, the user's operating system will ensure that this
code is present for at least five seconds before deactivating the SF line loopback
(MT8976/77 Remote Loopback).
The MT8926 will detect this repeating bit pattern even in the presence of a BER of
3 errors in 1000 bits.
Line Loopback Enable Detect. This bit is set when a repeating 00001 pattern
(either framed or unframed) is detected in the received T1 signal for at least five
frames. In order to comply with T1.403, the user's operating system will ensure
that this code is present for at least five seconds before activating the SF line
loopback (MT8976/77 Remote Loopback).
The MT8926 will detect this repeating bit pattern even in the presence of a BER of
3 errors in 1000 bits.
Description
Data Sheet
SEMICMF.019