XRT72L13 Datasheet, PDF (281/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

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PRELIMINARY
XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
FIGURE 82. FLOW CHART DEPICT HOW TO USE THE LAPD TRANSMITTER
START
WRITE IN DATA LINK INFORMATION
The user accomplishes this by writing the
information that he/she wishes to transmit
(via the LAPD Transmitter) to locations 86h
through DDh, within the UNI Address Space.
CONFIGURE THE LAPD
TRANSMITTER FOR TRANSMISSION
This is accomplished by writing 00000xx1b
to the Tx DS3 LAPD Configuration Register.
(where xx dictates LAPD Message Type)
START TRANSMISSION OF LAPD
MESSAGE
This is accomplished by writing 000010x0b
to the Tx DS3 LAPD Status/Interrupt
Register. (where x indicates the user’s
choice to enable/disable “LAPD Message
Transfer Complete” Interrupt
LAPD Transmitter inserts Frame Header
octets in front of the user payload.
LAPD Transmitter computes the 16 bit FCS
(a CRC-16 value) and inserts it into the LAPD
Message, following the user payload
LAPD Transmitter appends a Flag Sequence
Trailer octet to the end of the LAPD Message
(after the 16 bit FCS).
Is
5 consecutive
Yes
“1s” detected
?
No
Insert a “0” after the
string of 5 consecutive
“1s”
Is
Message
No
Transmission
Yes
Complete
?
END
Generate Interrupt
LAPD Transmitter will
continue to transmit
Flag Sequence octets.
The Mechanics of Transmitting a New LAPD Mes-
sage
As mentioned above, after the LAPD Transmitter has
been enabled, and commanded to transmit the mes-
sage, residing in the "Transmit LAPD Message" buff-
er; it will continue to transmit this message at one-
second intervals. If the user wishes to transmit an-
other (e.g., different) PMDL message to the "Remote"
LAPD Receiver, he/she will have to write this "new"
message into the "Transmit LAPD Message" buffer,
via the Microprocessor Interface section of the Fram-
er. However, the user must be careful when writing in
this new message. If he/she writes this message into
OPERATING MODE REGISTER (ADDRESS = 0X00)
the "Transmit LAPD Message" buffer at the "wrong
time" (with respect to these "one-second" transmis-
sions), the user's action could interfere with these
transmissions; thereby causing the LAPD Transmitter
to transmit a "corrupted" message to the "Remote"
LAPD Receiver. In order to avoid this problem, while
writing the new message into the "Transmit LAPD
Message" buffer, the user should do the following:
1. Configure the Framer to automatically reset acti-
vated interrupts
The user can do this by writing a "1" into Bit 3 of the
Framer Operating Mode Register, as depicted below.
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Local Loop-
back
Mode
Line Loop-
back
Mode
Internal
LOS
Enable
RESET
Interrupt
Enable
Reset
Frame
Format
TimRefSel[1:0]
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