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PRELIMINARY
XRT79L71
128
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
STEP 5 - Specify the size of the outbound LAPD Message
This is accomplished by writing the size of the information payload in terms of number of bytes into the
Transmit LAPD Byte Count Register, as depicted below.
STEP 6 - Load the Transmit LAPD Message Buffer
The next step is to load into the contents of the outbound LAPD/PMDL Message into the Transmit LAPD
Message Buffer. Whenever the user wishes to load in the contents o the outbound PMDL/LAPD Message into
the Transmit LAPD Message buffer, then the user MUST employ an Indirect Addressing scheme that will be
presented below.
In order to begin the process of loading in the contents of the outbound PMDL Message, the user must be
aware of the following important Address Locations, within the XRT79L71 Address space.
1.
The LAPD Message Buffer - Indirect Address Register - Address = 0x11C0
2.
The LAPD Message Buffer - Indirect Data Register - Address = 0x11C1
By performing READ or WRITE operations to these two registers, the user can actually obtain READ/WRITE
access to both the Transmit LAPD Message Buffer and the Receive LAPD Message Buffer. This section will
describe the approach that one should use to access the Transmit LAPD Message Buffer. The approach that
one should use to access the Receive LAPD Message buffer will be presented in
Section 4.3.3.2.The exact approach that one should use, when loading the contents of their PMDL Message into the Transmit
LAPD Message buffer is presented below.
STEP 6a - Write the value "0x7E" into the very first byte-position, within the Transmit LAPD Message
Buffer.
This is accomplished by executing the following two sub-steps.
Sub-STEP 6a.1 - At Address Location 0x11C0 (The LAPD Message Buffer - Indirect Address Register)
write in the value "0x00".
This step will cause an internal LAPD Message Buffer pointer to point to the very first byte of Indirect Address
= 0x00 within the Transmit LAPD Message Buffer.
Sub-STEP 6a.2 - At Address Location 0x11C1 (the LAPD Message Buffer - Indirect Data Register) write
in the value "0x7E".
Transmit DS3 LAPD Configuration Register (Address = 0x1133)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LAPD Any
Unused
Auto
Retransmit
Unused
Transmit LAPD
Message Length
Transmit
LAPD Enable
R/W
RO
R/O
R/W
R/O
R/W
1
0
1
0
X
1
Transmit LAPD Byte Count Register (Address = 0x1183)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
TxLAPD_MESSAGE_SIZE[7:0]
R/W
X