XRT72L50
á
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
207
NOTES:
1.
The white (e.g., unshaded) boxes reflect tasks that the user’s system must perform in order to configure the
Receive FEAC Processor to receive FEAC messages.
2.
A brief description of the steps that must exist within the FEAC Validation and FEAC Removal Interrupt Service
Routines exists in
4.3.3.2
The Message Oriented Signaling (e.g., LAP-D) Processing via the Receive DS3 HDLC
Controller block
The LAPD Receiver (within the Receive DS3 HDLC Controller block) allows the user to receive PMDL
messages from the remote terminal equipment, via the inbound DS3 frames.
In this case, the inbound
message bits will be carried by the 3 DL bit-fields of F-Frame 5, within each DS3 M-Frame. The remote LAPD
Transmitter will transmit a LAPD Message to the Near-End Receiver via these three bits within each DS3
Frame. The LAPD Receiver will receive and store the information portion of the received LAPD frame into the
Receive LAPD Message Buffer, which is located at addresses: 0xDE through 0x135 within the on-chip RAM.
The LAPD Receiver has the following responsibilities.
Framing to the incoming LAPD Messages
Filtering out stuffed “Zeros” (Between the two flag sequence bytes, 0x7E)
Storing the Frame Message into the Receive LAPD Message Buffer
Perform Frame Check Sequence (FCS) Verification
Provide status indicators for
FIGURE 72. FLOW DIAGRAM DEPICTING HOW THE RECEIVE FEAC PROCESSOR FUNCTIONS
START
ENABLE THE “FEAC REMOVAL AND
“VALIDATION” INTERRUPTS.
This is accomplished by writing “xxxx 1010” into the
“RxDS3 FEAC Interrupt/Status Register (Address = 0x17)
ENABLE THE “FEAC REMOVAL AND
“VALIDATION” INTERRUPTS.
This is accomplished by writing “xxxx 1010” into the
“RxDS3 FEAC Interrupt/Status Register (Address = 0x17)
RECEIVE FEAC PROCESSOR BEGINS READING IN
THE FEAC BIT-FIELDS (OF INCOMING DS3 FRAMES)
The Receive FEAC Processor checks for the “FEAC Framing
Alignment” pattern of “01111110”.
RECEIVE FEAC PROCESSOR BEGINS READING IN
THE FEAC BIT-FIELDS (OF INCOMING DS3 FRAMES)
The Receive FEAC Processor checks for the “FEAC Framing
Alignment” pattern of “01111110”.
Is the
“FEAC Framing
Alignment”pattern
present in the FEAC
Channel
?
Is the
“FEAC Framing
Alignment”pattern
present in the FEAC
Channel
?
READ IN THE “6-BIT FEAC CODE WORD”
The 6-bit FEAC Code Word immediately follows the “FEAC
Framing Alignment” Pattern.
READ IN THE “6-BIT FEAC CODE WORD”
The 6-bit FEAC Code Word immediately follows the “FEAC
Framing Alignment” Pattern.
Has this
same FEAC
Code Word been
Received in 8 out of the last
10 FEAC Message
Receptions?
Has this
same FEAC
Code Word been
Received in 8 out of the last
10 FEAC Message
Receptions?
Has a FEAC
Code Word (other than
the last “Validated Code Word)
been Received in 3 out of the last
10 FEAC Message
Receptions?
Has a FEAC
Code Word (other than
the last “Validated Code Word)
been Received in 3 out of the last
10 FEAC Message
Receptions?
GENERATE “FEAC
VALIDATION” INTERRUPT
GENERATE “FEAC
VALIDATION” INTERRUPT
INVOKE “FEAC VALIDATION”
INTERRUPTSERVICE ROUTINE.
INVOKE “FEAC VALIDATION”
INTERRUPTSERVICE ROUTINE.
GENERATE “FEAC
REMOVAL” INTERRUPT
GENERATE “FEAC
REMOVAL” INTERRUPT
INVOKE “FEAC REMOVAL”
INTERRUPTSERVICE ROUTINE.
INVOKE “FEAC REMOVAL”
INTERRUPTSERVICE ROUTINE.
1
NO
YES
NO
YES