XRT72L56 Datasheet, PDF (256/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L56 SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
that the bit, that it is currently sampling via the RxSer
pin is an overhead bit and should not be processed.
The Behavior of the Signals between the Receive
Payload Data Output Interface block and the Ter-
minal Equipment
The behavior of the signals between the XRT72L56
and the Terminal Equipment for DS3 Serial Mode Op-
eration is illustrated in Figure 94.
FIGURE 94. AN ILLUSTRATION OF THE BEHAVIOR OF THE SIGNALS BETWEEN THE RECEIVE PAYLOAD DATA OUTPUT
INTERFACE BLOCK OF THE XRT72L56 AND THE TERMINAL EQUIPMENT (SERIAL MODE OPERATION)
Terminal Equipment Signals
DS3_Clock_In
DS3_Data_In
Rx_Start_of_Frame
DS3_Overhead_Ind
Payload[4702] Payload[4703]
X-Bit
Payload[0]
XRT72L5x Receive Payload Data I/F Signals
RxClk
RxSer
Payload[4702] Payload[4703]
RxFrame
RxOH_Ind
X-Bit
Payload[0]
DS3 Frame Number N
Note: RxFrame pulses high to denote
DS3 Frame Boundary.
Note: RxOH_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.
4.3.5.2 Nibble-Parallel Mode Operation
Behavior of the XRT72L56
If the XRT72L56 has been configured to operate in
the Nibble-Parallel Mode, then the XRT72L56 will be-
have as follows.
Payload Data Output
The XRT72L56 will output the payload data of the in-
coming DS3 frames, via the RxNib[3:0] output pins,
upon the falling edge of RxClk.
NOTES:
1. In this case, RxClk will function as the Nibble Clock
signal between the XRT72L56 the Terminal Equip-
ment. The XRT72L56 will pulse the RxClk output
signal "High" 1176 times, for each inbound DS3
frame.
2. Unlike Serial Mode operation, the duty cycle of
RxClk, in Nibble-Parallel Mode operation is approx-
imately 25%.
Delineation of Inbound DS3 Frames
The XRT72L56 will pulse the RxFrame output pin
"High" for one nibble-period coincident with it driving
the very first nibble, within a given inbound DS3
frame, via the RxNib[3:0] output pins.
Interfacing the XRT72L56 the Terminal Equip-
ment.
Figure 95 presents a simple illustration as how the
user should interface the XRT72L56 to that terminal
equipment which processes Receive Direction pay-
load data.
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