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PRELIMINARY
XRT79L71
314
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
Once the user executes this step, then the Transmit LAPD Controller will proceed to do the following.
a. It will parse through the contents of the Transmit LAPD Message buffer and will "zero-stuff" the payload
portion of the outbound PMDL Message.
b. It will compute and append the Frame Check Sequence (FCS) value, to the back end of the outbound
PMDL Message.
c. It will begin (in a bit-by-bit manner) inserting the resulting PMDL Message into the "N" bit-fields, within
the outbound E3 frames.
NOTES:
1.
After the user has set the Initiate Transmission of LAPD/PMDL Message bit to "1", the user is advised to (some
time later) to execute another write operation (to this register) that sets the Initiate Transmission of LAPD/PMDL
Message bit back to "0".
2.
Once the Transmit LAPD Controller has started to transmit the PMDL Message to the remote terminal, it will
denote this by setting the Transmit LAPD Controller Busy bit-field (within the Transmit E3 LAPD Status/Interrupt
register) to "1", as illustrated below.
This bit-field permits the user to poll the status of the Transmit LAPD Controller. Once the Transmit LAPD
Controller has completed the transmission of the LAPD Message frame, this bit-field will then toggle back to
"0".
5.2.3.2
Transmitting Non-Standard Variable Length (e.g., up to 82 bytes) LAPD Messages
The user can (1) write the contents of the outbound PMDL Message into the Transmit LAPD Message buffer
and (2) command the Transmit LAPD Controller to begin the transmission of this PMDL Message by executing
the following steps.
STEP 1 - Make sure that the XRT79L71 has been configured to operate in the E3, ITU-T G.751 Framing
format.
This is accomplished by reading out the contents of the Frame Operating Mode Register (Address = 0x1100)
and verifying that Bit 6 (DS3/E3*) is set to "0" and that Bit 2 (Frame Format) is set to "1", as illustrated below.
Transmit E3 LAPD Status/Interrupt Register (Address = 0x1134)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
Initiate
Transmission
of
LAPD/PMDL
Message
Transmit
LAPD
Controller
Busy
Transmit
LAPD
Interrupt
Enable
Transmit
LAPD
Interrupt
Status
RO
R/W
RO
R/W
RUR
0
0-> 1
0
1
0
Transmit E3 LAPD Status/Interrupt Register (Address = 0x1134)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
Initiate
Transmission
of
LAPD/PMDL
Message
Transmit
LAPD
Controller
Busy
Transmit
LAPD
Interrupt
Enable
Transmit
LAPD
Interrupt
Status
RO
R/W
RO
R/W
RUR
0
1
0