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XRT79L71
PRELIMINARY
287
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
TxOH_Ind output pin, in this case DOES have meaning. In Mode 6 Operation, the XRT79L71 will pulse its
TxOH_Ind output pin "High" one nibble-period prior to the instant that it will process a given Overhead nibble
within the outbound E3 frame. Since the TxOH_Ind output pin of the XRT79L71 is electrically connected to the
E3_Overhead_Ind input pin of the System-Side Terminal Equipment, whenever the XRT79L91 device pulses
its TxOH_Ind output pin "High", it will also drive the E3_Overhead_Ind input pin of the System-Side Terminal
Equipment "High". Whenever the System-Side Terminal Equipment detects this pin toggling "High" it should
delay the transmission of the very next E3 payload nibble by one TxNibClk clock period.
NOTE: Since the E3, ITU-T G.751 Frame consists of 12 overhead bits, whenever the TxOH_Ind output pin of the XRT79L71
pulses "High" it will do so for three (3) consecutive nibble-periods when processing the FAS, A and N bits.
Therefore, for the E3, ITU-T G.751 framing format, whenever the System-Side Terminal Equipment detects the
TxOH_Ind output pin being pulled "High", it is expected to (1) continuously sample the state of the TxOH_Ind
output pin with each rising edge of TxNibClk and (2) to NOT transmit an E3 payload bit to the Transmit Payload
Data Input Interface block until it samples the TxOH_Ind output pin toggling "Low".
The Frequency of TxNibClk for E3, Nibble-Parallel Mode Operation
In contrast to that for the DS3 framing formats, for E3 Applications (both ITU-T G.832 and ITU-T G.751 framing
formats) the frequency of the TxNibClk clock signal is exactly one-fourth of the frequency of the TxInClk signal.
Figure 135 presents an illustration of the behavior of the System-Side Terminal Equipment/Transmit Payload
Data Input Interface signals for Mode 6 Operation.
Configuring the XRT79L71 to operate in Mode 6 (Nibble-Parallel/Local-Timing/Frame Master Mode)
FIGURE 135. AN ILLUSTRATION OF THE BEHAVIOR OF THE SYSTEM-SIDE TERMINAL EQUIPMENT SIGNALS FOR MODE
6 (NIBBLE-PARALLEL/LOCAL-TIMING/FRAME MASTER) MODE OPERATION
System-Side Terminal Equipment Signals
TxInClk
Tx_End_of_Frame
E3_Nib_Clock_In
E3_Data_Out[3:0]
Payload Nibble [380]
Overhead Nibble [0]
XRT79L71 Transmit Payload Data Input Interface Signals
E3 Frame Number N
E3 Frame Number N + 1
Note: TxNibFrame pulses high to denote
E3 Frame Boundary.
TxInClk
TxNibFrame
TxNibClk
TxNib[3:0]
Payload Nibble [380]
Overhead Nibble [0]
Sampling Edge of XRT79L71 Device
E3_OH_Ind
TxOH_Ind
TxOH_Ind toggles to
Denote Overhead Nibble