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PRELIMINARY
XRT79L71
484
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
STEP 7 - 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 SEE”RECEIVING NON- 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 7a - 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 7a.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 7a.2 - At Address Location 0x11C1 (The LAPD Message Buffer - Indirect Data Register) write
in the value "0x7E".
This step will cause the value "0x7E" to be written into the location that is being identified by the LAPD
Message Buffer pointer. In this case, (per Sub-STEP 7a.1, above) this will be the very first byte of Indirect
Address 0x00 within the Transmit LAPD Message Buffer.
STEP 7b - Write in the remaining bytes of this outbound message into the Transmit LAPD Message
Buffer.
This is accomplished by executing the procedure that is defined and presented within the following flow-chart.
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