
XRT84L38
414
OCTAL T1/E1/J1 FRAMER
REV. 1.0.1
13.2.3.1.4
Step 4: Read BOS Message from receive data link buffer
Upon detection of the Receive End of Transfer (RxEOT) interrupt, the user should read the Message Type bit
of the Data Link Status Register (DLSR) to find out what is the type of message received.
The table below shows how contents of the Message Type bit of the Data Link Status Register (DLSR)
determines what the type of message received in the data link channel is.
DATA LINK STATUS REGISTER (DLSR) (INDIRECT ADDRESS = 0XNAH, 0X06H)
After determined that the received message is a BOS one, the use should read eight bits message from the
first location of the next available receive data link buffer. The reading of these buffers is through the LAPD
Buffer 0 indirect data registers and the LAPD Buffer1 indirect data registers. LAPD Buffer 0 and 1 indirect data
registers have addresses 0xn6H and 0xn7H respectively. There is no indirect address register for receive data
link buffer 0 and 1.
A microcontroller WRITE access to the LAPD Buffer indirect data registers will access the receive data link
buffer and a microcontroller READ will access the receive data link buffers. The very first READ access to the
LAPD Buffer indirect data register will always be direct to location 0 within the receive data link buffer.
For example, if the BOS Message to received is (101011) and the next available receive data link buffer of
Channel n is 1. The user should be able to read pattern (01010110) from receive data link buffer 1 of Channel
n. The following microprocessor access to the framer should be done:
RD
n7H
The result of the READ access should be 0x56H.
13.2.4
Receive LAPD Controller
The receive LAPD controller implements the Message-Oriented protocol based on ITU Recommendation
Q.921 Link Access Procedures on the D-channel (LAPD) type of protocol. It provides the following functions:
Zero deletion
Pattern recognition for IDLE flag detection
Pattern recognition for ABORT sequence detection
Frame check sequence verification
T1 receiver interface
Receive data link message buffer access
RECEIVE DATA LINK BYTE COUNT REGISTER (RDLBCR) (INDIRECT ADDRESS = 0XN0H, 0X15H)
B
IT
N
UMBER
B
IT
N
AME
B
IT
T
YPE
B
IT
D
ESCRIPTION
6-0
Receive Data Link
Byte Count [6:0]
R/W
Value of these bits determines how many times a BOS message pattern
will be received by the framer before generating the Receive End of Trans-
fer (TxEOT) interrupt.
N
OTE
:
If these bits are set to 0, the BOS message will be received
indefinitely and no Receive End of Transfer interrupts will be
generated.
B
IT
N
UMBER
B
IT
N
AME
B
IT
T
YPE
B
IT
D
ESCRIPTION
7
Message Type
RUR /
WC
0 - There is no BOS ABORT sequence received in the data link channel.
1 - The HDLC Controller receives BOS ABORT sequence in the data link
channel.