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XRT79L71
PRELIMINARY
421
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
Configuring the XRT 79L71 to operate in the Nibble-Parallel Mode
The XRT79L71 can be configured to operate in the Nibble-Parallel Mode by executing the following steps.
STEP 1 - Design your board such that the System-Side Terminal Equipment circuitry interfaces to the
Receive Payload Data Input Interface in the manner as depicted above in Figure 189.
STEP 2 - Configure the XRT 79L71 to operate in the Nibble-Parallel Mode
This can be accomplished by setting the "NibIntf" input pin to a logic "HIGH".
NOTE: This step also configures the "Transmit Payload Data Input Interface" block to operate in the "Nibble-Parallel Mode".
6.0
ARCHITECTURAL/FUNCTIONAL DESCRIPTION OF THE XRT 79L71 - E3, ITU-T G.832 MODE
OPERATION
This particular section discusses Clear-Channel Framer over E3, ITU-T G.832 operation of the XRT79L71.
Prior to discussing the architecture and the role of the DS3/E3 Framer blocks, whenever the XRT79L71 has
been configured to operate in the E3, ITU-T G.832 Mode; it is imperative to discuss the E3, ITU-T G.832 Frame
structure.
6.1
DESCRIPTION OF THE E3, ITU-T G.832 FRAME STRUCTURE AND OVERHEAD BITS
The E3, ITU-T G.832 frame contains 537 bytes, of which 7 bytes are overhead bytes and the remaining 530
bytes are payload bytes.
These 537 octets are arranged in a 9 rows of 60 byte columns each, except for the last three rows, which
contain only 59 byte columns. The frame repetition rate for this type of E3 frame is 8000 times per second,
thereby resulting in the standard E3 bit-rate of 34.368Mbps.Figure 194 presents an illustration of the E3, ITU-
T G.832 Frame Format.
FIGURE 193. AN ILLUSTRATION OF THE BEHAVIOR OF THE "SYSTEM-SIDE TERMINAL EQUIPMENT" SIGNALS FOR
"NIBBLE-PARALLEL MODE" OPERATION
System-Side Terminal Equipment Signals
XRT79L71 Transmit Payload Data Input Interface Signals
E3 Frame Number N
E3 Frame Number N + 1
Note: RxFrame pulses high to denote
E3 Frame Boundary.
Rx_Start_of_Frame
E3_Nib_Clock_In
E3_Data_In[3:0]
FAS Byte – Bits 1 - 4
FAS Byte – Bits 5 - 8
RxClk
RxFrame
RxNib[3:0]
FAS Byte – Bits 1 - 4
FAS Byte – Bits 5 - 8
RxOH_Ind
Rx_E3_Overhead_Ind