XRT72L52
REV. 1.0.1
xr
TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
420
(Address = 0x1C). Once this occurs, the Receive E3 Framer block will notify the Microprocessor of this new in-
coming Trail Trace Buffer message by generating the Change in Trail Trace Buffer Message interrupt. The Re-
ceive E3 Framer block will also set bit 6 (TTB Change Interrupt Status) within the Rx E3 Framer Interrupt Sta-
tus Register - 2, as depicted below.
The contents of the TR byte-field, in the very next E3 frame will be written into the Rx TTB-1 Register (Address
= 0x1D), and so on until all 16 bytes have been received.
N
OTES
:
1. Anytime the Receive E3 Framer block receives an E3 frame that contains an octet in the TR byte-field, with a “1” in
the MSB (Most Significant Bit) position, then the Receive E3 Framer block will (1) write the contents of the TR byte-
field (in this E3 frame) into the RxTTB-0 Register,
2. It will generate the Change in Trail Trace Buffer Interrupt. The Receive E3 Framer will do these things independent
of the number of E3 frames that have been received since the last occurrence of the Change in Trail Trace Buffer
Interrupt. Hence, the user, when writing data into the Tx TTB registers, must take care to insure that only the Tx
TTB-0 register contains an octet with a “1” in the MSB position. All remaining Tx TTB registers (e.g., TxTTB-1
through TxTTB-15) must contain octets with a “0” in the MSB position.
3. The Framer IC will not verify the CRC-7 value that is written into the Rx TTB-0” register. It is up to the user’s sys-
tem hardware and/or software to perform this verification.
6.3.3
The Receive HDLC Controller Block
The Receive E3 HDLC Controller block can be used to receive message-oriented signaling (MOS) type data
link messages from the remote terminal equipment.
The MOS types of HDLC message processing is discussed in detail below.
The Message Oriented Signaling (e.g., LAP-D) Processing via the Receive E3 HDLC Controller block
The LAPD Receiver (within the Receive E3 HDLC Controller block) allows the user to receive PMDL messages
from the remote terminal equipment, via the Inbound E3 frames. In this case, the Inbound message bits will be
carried by either the GC or the NR byte-fields within each E3 Frame. The remote LAPD Transmitter will trans-
mit a LAPD Message to the Near-End Receiver via either one of these bytes within each E3 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 Re-
ceiver has the following responsibilities.
Framing to the incoming LAPD Messages
Filtering out stuffed "0’s" (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
End of Message (EOM)
Flag Sequence Byte detected
Abort Sequence detected
Message Type
RXE3 INTERRUPT STATUS REGISTER - 2 (ADDRESS = 0X15)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Not Used
TTB
Change
Interrupt
Status
Not Used
FEBE
Interrupt
Status
FERF
Interrupt
Status
BIP-8
Error Interrupt
Status
Framing
Byte Error
Interrupt
Status
RxPld
Mis
Interrupt
Status
RO
RUR
RO
RUR
RUR
RUR
RUR
RUR
0
1
0
0
0
0
0
0