mt8926ap Mitel, mt8926ap Datasheet - Page 12

• Manufacturer Part Number: mt8926ap
• Description: Iso-cmos T1 Performance Monitoring Adjunct Circuit Pmac
• Manufacturer: Mitel

MT8926
Alarm Indication Signal (AIS)
An AIS or Blue alarm is an all ones signal that can be
transmitted from the network side to the terminal
equipment side of an interface or from the terminal
equipment side to the network side of an interface. In
the first case, it indicates that the T1 signal from the
network may be lost, and the timing that the terminal
equipment derives from the received AIS may not be
from the network. In the second case, it indicates
that data from the terminal equipment side of an
interface has been lost and AIS is being transmitted
in its place.
The MT8926 will detect an AIS alarm and indicate its
presence by making the AIS bit of Master Status
Word 2 (Table 11, CSTo channel 31 bit 0) high. This
state
synchronization and less than three zeros are
detected in any 250 microsecond interval. The AIS
bit will go low when either of these conditions is no
longer true.
MT8926 FDL Message Transfer
The MT8926 will support the transfer of FDL bit-
oriented messages in a format that is consistent with
T1.403 and T1.408. A BOM is transmitted by loading
the message into the PMAC Transmit Bit-Oriented
Message Register (TxBOM), Table 13, CSTi1
Channel 7. This data has the form 0XXXXXX0,
where XXXXXX is the content of the T1.403/408
message. When FDLEn (bit zero of the PMAC
4-14
7-0
7-0
Bit
Bit
occurs
RxBOM
TxBOM
Name
Name
when
Table 13. Transmit Bit-Oriented Message Register (CSTi1 Channel 7)
Table 12. Receive Bit-Oriented Message Register (CSTo Channel 27)
the
Received Bit-Oriented Message. This register contains the eight least significant
bits of the ESF bit oriented message codeword. The contents of this register is valid
when a bit-oriented message codeword is received by the MT8926 in the facility
data link bit positions of consecutive extended superframes. A valid codeword will
have the form 111111110XXXXXX0. The most significant eight bits (FF sequence)
are received first. The register will contain the eight bits following the 11111111
sequence, which are 0XXXXXX0.
When a valid codeword is detected, bit zero of the PMAC Miscellaneous Status
Register is set.
Transmit Bit-Oriented Message. The contents of this register will be appended to an
FF flag to form a bit-oriented codeword, and clocked out on FDLo when bit zero in
the PMAC Control Word is set high. The MT8926 will continue to clock this message
out until bit 0 in the Control word is reset. The order of transmission is Bit 7 first.
Bits 7 and 0 should be zero for a code word to be valid.
MT8976/77
has
lost
Control Word, Table 14) is made high, the BOM is
transmitted on the FDL preceded by 11111111. The
start of the bit-oriented message is not synchronous
with FDLEn going high. Therefore, to ensure a
message is sent a minimum of n times, the message
must be transmitted for 32n + 32 ST-BUS frames.
Valid codewords that are received on the FDL are
loaded into the Receive Bit-Oriented Message
Register (RxBOM, see Table 12). A codeword is valid
if it fits the 11111111 0XXXXXX0 form, however, only
the 0XXXXXX0 portion of the message will appear in
the RxBOM register. When a valid codeword has
been
Miscellaneous Status Word (Table 5, CSTo channel 7
bit 0) will be high. If the next received codeword is
not valid, the BOMV bit will become zero and the
RxBOM register will retain its most recent valid
message.
The MT8926 will support LAPD message-oriented
performance reporting when it is combined with an
HDLC controller such as the MT8952. See Figure 7
for FDL operation. The performance monitoring data
that makes up the LAPD message is derived by the
combination of MT8976/77 T1 framer and MT8926
PMAC, and is available on CSTo. This data can then
be assembled into a LAPD message and presented
to the MT8952 HDLC controller for transmission over
the FDL on a one second basis as per T1.403/408
(see Figure 10). FDLEn of the PMAC Control Word
(CSTi1 channel 11 bit 0) must be low to allow
transmission of a performance report from the HDLC
controller through pins FDLi and FDLo of the
Description
Description
received
the
BOMV
bit
of the
PMAC