XR72L52 Datasheet, PDF (292/480 Pages) Exar Corporation – TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L52
REV. 1.0.1
xr
TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
FIGURE 106. FLOW CHART DEPICTING HOW TO USE THE LAPD TRANSMITTER
START
LAPD Transm itter inserts Fram e Header
octets in front of the user payload.
Write the Header in 0x86 to 0x89
Write in Data Link Information
This is accom plished by writing the inform ation
to be transm itted via the LAPD Transm itter to
locarions, 0x8A thru 0xDB in the Fram er
address space.
Enable the LAPD Transmitter for
T ran sm issio n
This is done by writing the value 00000xx1b
into the Tx DS3 LAPD Configuration Register.
(xx dictates the LAPD Message Length)
Initiate Transmission of LAPD Message
This is done by writing the value 000010x0b
into the Tx DS3 LAPD Status/Interrupt
Register.
(x indictates that the user can choose to
enable/disable the LAPD Message Transfer
Com plete Interrupt)
LAPD Transm itter com putes the 16 bit FCS
(a CRC-16 value) over the Header and
Payload bytes and inserts it into the LAPD
Message, following the user payload.
LAPD Transm itter appends a Flag Sequence
Trailer octet to the end of the LAPD
Message after the 16 bit FCS.
Are 5
Consecutive
"Ones" detected
between the
YES
start and end flag
sequence
?
NO
Insert a "0" after
the string of 5
consecutive "1's"
Is
NO
Message
T ransm ission
Com plete
?
YES
END
Generate Interrupt LAPD Transm itter will
continue to transm it Flag Sequence octets.
NOTE: In Figure 106, the unshaded boxes depict the tasks that the user must perform. The shaded boxes present the
resulting tasks that the Transmit HDLC Controller block will perform.
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-second
intervals, then it will repeatedly transmit the LAPD Message frame 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
276