XRT72L50 Datasheet, PDF (281/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
FIGURE 104. BEHAVIOR OF TRANSMIT OVERHEAD DATA INPUT INTERFACE SIGNALS BETWEEN THE XRT72L50 AND
THE TERMINAL EQUIPMENT (FOR METHOD 2)
TxInClk
TxOHFrame
TxOHEnable
TxOHIns
TxOH
TxOHEnable Pulse # 0
TxOHEnable Pulse # 10
A bit = 1
Terminal Equipment
samples “TxOHFrame” and
“TxOHEnable” being “HIGH”
Terminal Equipment counts the number of
TxOHEnable pulses. At “pulse # 10” the Terminal
Equipment asserts the “TxOHIns” signal and places the
desired data on TxOH.
XRT72L5x samples TxOH
here.
5.2.3 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 discussed in detail below.
5.2.3.1
Message-Oriented Signaling (e.g., LAP-D) processing via the Transmit E3 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 remote terminal via the outbound E3 Frames. In this case the
message bits are inserted into and carried by the N bit, within the outbound E3 frames. The on-chip LAPD
transmitter supports 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
message format complies with ITU-T Q.921 (LAP-D) protocol with different addresses and is presented below
in Figure 105 .
NOTE: {(Header = 4bytes) + (Payload = 82 bytes max) = 86 bytes + FCS = 2 bytes} = 88 bytes. But, FCS is always
computed by the Framer. The user must write a max of 86 bytes only.
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