XR72L52 Datasheet, PDF (401/480 Pages) Exar Corporation – TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
XRT72L52
REV. 1.0.1
FIGURE 164. FLOW CHART DEPICTING HOW TO USE THE LAPD TRANSMITTER (LAPD TRANSMITTER IS CONFIGURED
TO TRANSMIT A LAPD MESSAGE FRAME ONLY ONCE).
Start
Write the Header in 0x86 to 0x89
LAPD Transmitter will generate a continuous string
of Flag Sequence bytes that will be transported via
the GC or the NR byte-fileld (user's selection)
Write the LAPD Message frame identification octet into
the first octet position within the Transmit LAPD Message
buffer (Address=0x8A)
Write the PMDL Message into the remaining portion of
the Transmit LAPD Message buffer (from 0x87 to 0xDB)
Specify the type/size of the LAPD Message frame to be
transmitted.
Write the appropriate value into bit 1 within the Transmit
E3 LAPD Configuration Register
Specify whether the outbound LAPD Message frame is to
be transported via the GC or the NR byte-fields within
each outbound E3 frame
Initiate the LAPD Message transmission
LAPD Transmitter will compute and insert the FCS
value into the LAPD Message frame.
LAPD Transmitter will "stuff" the contents of the
PMDL Message and FCS Bytes
LAPD Transmitter will fragment LAPD Message
frame into octets and begin to insert these into
the GC or NR byte-field (user's selection) into each
outbound E3 frame.
Complete transmission of LAPD Message frame
Configure the LAPD Transmitter to repeat transmissions
of the LAPD Message frame at one second intervals
Generate Completion of Transmission LAPD
Message Frame Interrupt
Enable the LAPD Transmitter
Halt transmission. Wait until the LAPD Message
Frame Transmission is initiated again
The Mechanics of Transmitting a New LAPD Message frame, if the LAPD Transmitter has been config-
ured to re-transmit the LAPD Message frame, repeatedly, at One-Second intervals.
If the LAPD Transmitter has been configured to retransmit the LAPD Message frame repeatedly at One-Sec-
ond intervals, then it will repeatedly transmit the stuffed PMDL Message to the Remote Terminal Equipment at
one second intervals.
If another (e.g., a different) PMDL Message is to be transmitted to the Remote Terminal Equipment this new
message will have to be written into the Transmit LAPD Message buffer, via the Microprocessor Interface block
of the Framer IC. However, care must be taken when writing this new PMDL message. If this message is writ-
ten into the Transmit LAPD Message buffer at the wrong time (with respect to these One-Second LAPD Mes-
sage frame transmissions), the user’s action could interfere with these transmissions, thereby causing the
LAPD Transmitter to transmit a corrupted message to the Remote Terminal Equipment. In order to avoid this
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