XRT72L56 Datasheet, PDF (402/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
Method 2) in order to transmit a Yellow Alarm to
the remote terminal equipment.
In this case, the Terminal Equipment intends to insert
the appropriate overhead bits, into the Transmit Over-
head Data Input Interface such that the XRT72L56
will transmit a Yellow Alarm to the remote terminal
equipment. Recall that, for E3, ITU-T G.832 applica-
tions, a Yellow Alarm is transmitted by setting the
FERF bit (within the MA byte) to "1".
If one assumes that the connection between the Ter-
minal Equipment and the XRT72L56 is as illustrated
in Figure 172 then, Figure 173 presents an illustration
of the signaling that must go on between the Terminal
Equipment and the XRT72L56.
FIGURE 173. BEHAVIOR OF TRANSMIT OVERHEAD DATA INPUT INTERFACE SIGNALS BETWEEN THE XRT72L56 AND
THE TERMINAL EQUIPMENT (FOR METHOD 2)
TxInClk
TxOHFrame
TxOHEnable
TxOHIns
TxOH
TxOHEnable Pulse # 0
TxOHEnable Pulse # 32
MA Byte, Bit 7
Terminal Equipment
samples “TxOHFrame” and
“TxOHEnable” being “HIGH”
Terminal Equipment counts the number of
TxOHEnable pulses. At “pulse # 32” the Terminal
Equipment asserts the “TxOHIns” signal and places the
desired data on TxOH.
XRT72L5x samples TxOH
here.
6.2.3 The Transmit E3 HDLC Controller
The Transmit E3 HDLC Controller block can be used
to transport Message-Oriented Signaling (MOS) type
messages to the remote terminal equipment as dis-
cussed in detail below.
NOTE: While executing this particular write operation, the
user should write the binary value "000xx110b" into the Tx
Controller block), please see Section 5.3.3.1.
6.2.3.1 Message-Oriented Signaling (e.g.,
LAP-D) processing via the Transmit DS3 HDLC
Controller
The LAPD Transmitter (within the Transmit E3 HDLC
Controller Block) allows the user to transmit path
maintenance data link (PMDL) messages to the re-
mote terminal via the Outbound E3 Frames. In this
case the message bits are either inserted into and
carried by the “NR” or the “GC” bytes, within the Out-
bound E3 frames. The on-chip LAPD transmitter sup-
ports both the 76 byte and 82 byte length message
formats, and the Framer IC allocates 88 bytes of on-
chip RAM (e.g., the Transmit LAPD Message buffer)
to store the message to be transmitted. The mes-
sage format complies with ITU-T Q.921 (LAP-D) pro-
tocol with different addresses and is presented below
in Figure 174.
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