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PRELIMINARY
XRT79L71
122
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
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 4.3.3.1.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 5a - 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 5a.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 5a.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 5a.1, above) this will be the very first byte of Indirect
Address 0x00 within the Transmit LAPD Message Buffer.
STEP 5b - Write the value for SAPI, C/R and EA0 into the second byte-position, within the Transmit
LAPD Message Buffer
This is accomplished by executing the following two sub-steps.
NOTE: Bellcore mandates that the user use the values "0x3C" or "0x3E" for the value of SAPI, C/R and EA0.
Sub-STEP 5b.1 - At Address Location 0x11C0 (The LAPD Message Buffer - Indirect Address Register)
write in the value "0x01".
This step will cause the internal LAPD Message Buffer pointer to point to the second byte of Indirect Address
0x01 within the Transmit LAPD Message Buffer.
Sub-STEP 5b.2 - At Address Location 0x11C1 (The LAPD Message Buffer - Indirect Data Register) write
in the value "0x3C" or "0x3E" for the value of SAPI, C/R and EA0.
This step will cause the value "0x3C" or "0x3E" to be written into the location that is being identified by the
LAPD Message Buffer pointer. In this case (per Sub-STEP 5b.1, above) this will be the second byte of Indirect
Address 0x01 within the Transmit LAPD Message Buffer
STEP 5c - Write the value for TEI and EA1 into the third byte-position, within the Transmit LAPD
Message Buffer
This is accomplished by executing the following two sub-steps.
NOTE: Bellcore mandates that the user use the value of "0x01" for this byte.
Sub-STEP 5c.1 - At Address Location 0x11C0 (The LAPD Message Buffer - Indirect Address Register)
write the value "0x02".
This step will cause the internal LAPD Message Buffer pointer to point to the third byte of Indirect Address
0x02 within the Transmit LAPD Message Buffer.
Sub-STEP 5c.2 - At Address Location 0x11C1 (The LAPD Message Buffer - Indirect Data Register) write
the value "0x01".
This step will cause the value "0x01" to be written into the location that is being identified by the LAPD
Message Buffer pointer. In this case (per Sub-STEP 5c.1, above) this will be the third byte of Indirect Address
0x02 within the Transmit LAPD Message Buffer.
STEP 5d - Write in the CONTROL BYTE value of 0x03 into the fourth byte-position, within the Transmit
LAPD Message buffer