XRT7250 Datasheet, PDF (237/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250 DS3/E3 FRAMER IC
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REV. 1.1.1
Operation of the Receive Payload Data Output In-
terface block
The Receive Payload Data Output Interface permits
the user to read out the payload data of inbound DS3
frames, via either of the following modes.
• Serial Mode
• Nibble-Parallel Mode
Each of these modes are described in detail, below.
4.3.5.1 Serial Mode Operation
Behavior of the XRT7250
If the XRT7250 has been configured to operate in the
Serial mode, then the XRT7250 will behave as fol-
lows.
Payload Data Output
The XRT7250 will output the payload data, of the in-
coming DS3 frames via the RxSer output, upon the
rising edge of RxClk.
Delineation of inbound DS3 Frames
The XRT7250 will pulse the RxFrame output pin
"High" for one bit-period, coincident with it driving the
first bit within a given DS3 frame, via the RxSer out-
put pin.
Interfacing the XRT7250 to the Receive Terminal
Equipment
Figure 93 presents a simple illustration as how the
user should interface the XRT7250 to that terminal
equipment which processes Receive Direction pay-
load data.
FIGURE 93. ILLUSTRATION OF THE XRT7250 DS3/E3 FRAMER IC BEING INTERFACED TO THE RECEIVE TERMINAL
EQUIPMENT (SERIAL MODE OPERATION)
Rx_DS3_Clock_In
DS3_Data_In
Rx_Start_of_Frame
Rx_DS3_OH_Ind
44.736 MHz Clock Signal
RxClk
RxSer
RxFrame
RxOHIns
44.736 MHz
Clock Source
RxLineClk
Terminal Equipment
(Receive Payload Section)
XRT7250 DS3 Framer
Required Operation of the Terminal Equipment
The XRT7250 will update the data on the RxSer out-
put pin, upon the rising edge of RxClk. However, be-
cause the rising edge of RxClk to data delay is be-
tween 14ns to 16ns, the Terminal Equipment should
sample the data on the RxSer output pin (or the
DS3_Data_In pin at the Terminal Equipment) upon
the rising edge of RxClk. This will still permit the Ter-
minal Equipment with a RxSer to RxClk set-up time of
approximately 6ns and a hold time of 14 to 16ns. As
the Terminal Equipment samples RxSer with each ris-
ing edge of RxClk it should also be sampling the fol-
lowing signals.
• RxFrame
• RxOHInd
The Need for sampling RxFrame
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