XRT74L73 Datasheet, PDF (188/488 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
turn, the TxFrameRef input pin of the XRT74L73),
"High" for one-bit period, coincident with the first bit of
a new DS3 frame. Once the XRT74L73 detects the
rising edge of the input at its TxFrameRef input pin, it
will begin generation of a new DS3 frame.
NOTES:
1. In this case, the Terminal Equipment is controlling
the start of Frame Generation, and is therefore
referred to as the Frame Master. Conversely, since
the XRT74L73 does not control the generation of a
new DS3 frame, but is rather driven by the Terminal
Equipment. Hence, the XRT74L73 is referred to as
the Frame Slave.
2. If the XRT74L73 is configured to operate in Mode
2, it is imperative that the Tx_Start_of_Frame (or
TxFrameRef) signal is synchronized to the TxInClk
input clock signal.
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 signals between the XRT74L73
and the Terminal Equipment for DS3 Mode 2 Opera-
tion is illustrated in Figure 54 .
FIGURE 54. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT74L73 AND THE TERMINAL
EQUIPMENT (MODE 2 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]
TxFrameRef
TxOH_Ind
X-Bit
Payload[1]
DS3 Frame Number N
DS3 Frame Number N + 1
Note: TxOH_Ind pulses high to
denote Overhead Data
Note: X-Bit will not be processed by the
Transmit Payload Data Input Interface.
(e.g., the X-bit).
Note: TxFrame pulses high to denote
DS3 Frame Boundary.
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 "01" as
depicted below.
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Local Loopback
R/W
0
DS3/E3*
R/W
0
Internal LOS
Enable
R/W
1
RESET Interrupt Frame Format
Enable Reset
R/W
R/W
R/W
0
1
0
TimRefSel[1:0]
R/W
R/W
0
1
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