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PRELIMINARY
XRT79L71
474
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
The user can (1) write the contents of an outbound PMDL Message, into the Transmit LAPD Message Buffer,
and (2) command the Transmit LAPD Controller to begin the transmission of this PMDL Message by executing
the following steps.
STEP 1 - Make sure that the XRT79L71 has been configured to operate in the E3, ITU-T G.832 Framing
format.
This is accomplished by reading out the contents of the Framer Operating Mode Register (Address = 0x1100)
and verifying that Bit 6 (DS3/E3*) is set to "0" and that Bit 2 (Frame Format) is set to "1", as illustrated below.
STEP 2 - Select either the NR or the GC byte as the LAPD Channel.
The user can accomplish this by writing the appropriate value into Bit 4 (Transmit LAPD in NR Byte), within the
Transmit E3 Configuration Register, as depicted below.
Setting this bit-field to "1" will configure the Transmit LAPD Controller block to use the NR byte as the LAPD
Channel. In this setting, the Transmit LAPD Controller block will fragment the contents of the outbound LAPD/
PMDL Message into bytes and it will insert each of these bytes into the NR byte-field position within each
outbound E3 frame. Conversely, setting this bit-field to "0" will configure the Transmit LAPD Controller block to
use the GC byte as the LAPD Channel. In this setting, the Transmit LAPD Controller block will fragment the
contents of each outbound LAPD/PMDL Message into bytes, and it will insert these bytes into the GC byte-
position within each outbound E3 frame.
STEP 3 - Enable the Transmit LAPD Controller
This is accomplished by setting Bit 0 (Transmit LAPD Enable) within the Transmit E3 LAPD Configuration
Register to "1", as illustrated below.
Framer Operating Mode Register (Address = 0x1100)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Local
Loop-back
DS3/E3*
Internal LOS
Enable
RESET
Direct
Mapped
ATM
Frame For-
mat
Timing Reference Select
[1:0]
R/W
X
0
X
0
X
1
X
Transmit E3 Configuration Register (Address = 0x1130)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Unused
Transmit
LAPD in NR
Byte
Unused
Transmit AIS
Enable
Transmit
LOS Enable
Transmit MA
based on
Receiver
R/O
R/W
R/O
R/W
0
X
0
X