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PRELIMINARY
EIGHT CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
XRT72L58
REV. P1.1.2
220
N
OTES
:
1. The white (e.g., unshaded) boxes reflect tasks that
the user’s system must perform in order to config-
ure 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 Section 3.6
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 0s (within the information pay-
load)
Storing the Frame Message into the Receive LAPD
Message Buffer
Perform Frame Check Sequence (FCS) Verification
Provide status indicators for
End of Message (EOM)
Flag Sequence Byte detected
Abort Sequence detected
Message Type
C/R Type
The occurrence of FCS Errors
F
IGURE
84. F
LOW
D
IAGRAM
DEPICTING
HOW
THE
R
ECEIVE
FEAC P
ROCESSOR
F
UNCTIONS
START
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”.
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.
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
GENERATE “FEAC
VALIDATION” INTERRUPT
.
INVOKE “FEAC VALIDATION”
INTERRUPTSERVICE ROUTINE
.
GENERATE “FEAC
REMOVAL” INTERRUPT
.
INVOKE “FEAC REMOVAL”
INTERRUPTSERVICE ROUTINE
.
1
1
1
1
1
1
NO
YES
YES
NO
NO
YES