XRT74L73 Datasheet, PDF (190/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
cessing the last bit-field within a given outbound DS3
frame. The Terminal Equipment is expected to moni-
tor the TxFrame signal (from the XRT74L73) and to
place the first bit, within the very next outbound DS3
frame on the TxSer input pin.
NOTE: In this case, the XRT74L73 dictates exactly when
the very next DS3 frame will be generated.
The Terminal Equipment is expected to respond ap-
propriately by providing the XRT74L73 with the first
bit of the new DS3 frame, upon demand. Hence, in
this mode, the XRT74L73 is referred to as the Frame
Master and the Terminal Equipment is referred to as
the Frame Slave.
Finally, the XRT74L73 will pulse its TxOH_Ind output
pin, one bit-period prior to it processing a given over-
head bit, within the outbound DS3 frame. Since the
TxOH_Ind output pin (of the XRT74L73) is electrically
connected to the DS3_Overhead_Ind whenever the
XRT74L73 pulses the TxOH_Ind output pin "High", it
will also be driving the DS3_Overhead_Ind input pin
(of the Terminal Equipment) "High". Whenever the
Terminal Equipment detects this pin toggling "High", it
should delay transmission of the very next DS3 frame
payload bit by one clock cycle.
The behavior of the signal between the XRT74L73
and the Terminal Equipment for DS3 Mode 3 Opera-
tion is illustrated in Figure 56 .
FIGURE 56. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT74L73 AND THE TERMINAL
EQUIPMENT (DS3 MODE 3 OPERATION)
Terminal Equipment Signals
DS3_Clock_In
DS3_Data_Out
Tx_Start_of_Frame
DS3_Overhead_Ind
Payload[4702] Payload[4703]
X-Bit
Payload[1]
XRT72L5x Transmit Payload Data I/F Signals
TxInClk
TxSer
Payload[4702] Payload[4703]
TxFrame
TxOH_Ind
X-Bit
Payload[1]
DS3 Frame Number N
Note: TxFrame pulses high to denote
DS3 Frame Boundary.
Note: TxOH_Ind pulses high to
denote Overhead Data
(e.g., the X-bit).
DS3 Frame Number N + 1
Note: X-Bit will not be processed by the
Transmit Payload Data Input Interface.
How to configure the XRT74L73 to operate in this
mode.
1. Set the NibIntf input pin "Low".
2. Set the TimRefSel[1:0] bit-fields (within the
Framer Operating Mode Register) to "10” or “11"
as depicted below.
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