XRT72L56 Datasheet, PDF (461/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
XRT72L56
SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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 E3
frames, via either of the following modes.
• Serial Mode
• Nibble-Parallel Mode
Each of these modes are described in detail, below.
6.3.5.1 Serial Mode Operation Behavior of the
XRT72L56
If the XRT72L56 has been configured to operate in
this mode, then the XRT72L56 will behave as follows.
Payload Data Output
The XRT72L56 will output the payload data, of the in-
coming E3 frames, upon the rising edge of RxClk.
Delineation of Inbound DS3 Frames
The XRT72L56 will pulse the RxFrame output pin
"High" for one bit-period, coincident with it driving the
first bit within a given E3 frame, via the RxSer output
pin.
Interfacing the XRT72L56 to the Receive Terminal
Equipment
Figure 209 presents a simple illustration as how the
user should interface the XRT72L56 to that terminal
equipment which processes Receive Direction pay-
load data.
FIGURE 209. ILLUSTRATION OF THE RECEIVE PAYLOAD DATA OUTPUT INTERFACE BLOCK (OF THE XRT72L56
DS3/E3 FRAMER IC) BEING INTERFACED TO THE RECEIVE TERMINAL EQUIPMENT (SERIAL MODE OPERATION)
Rx_E3_Clock_In
34.368 MHz Clock Signal
RxClk
34.368 MHz
Clock Source
E3_Data_In
Rx_Start_of_Frame
Rx_E3_OH_Ind
RxSer
RxFrame
RxOHInd
RxLineClk
Terminal Equipment
(Receive Payload Section)
XRT72L5x E3 Framer
Required Operation of the Terminal Equipment
The XRT72L56 will update the data on the RxSer out-
put pin, upon the rising edge of RxClk. Hence, the
Terminal Equipment should sample the data on the
RxSer output pin (or the E3_Data_In pin at the Termi-
nal Equipment) upon the rising edge of RxClk. As the
Terminal Equipment samples RxSer with each rising
edge of RxClk it should also be sampling the follow-
ing signals.
• RxFrame
• RxOHInd
The Need for sampling RxFrame
The XRT72L56 will pulse the RxFrame output pin
"High" coincident with it driving the very first bit of a
given E3 frame onto the RxSer output pin. If knowl-
edge of the E3 Frame Boundaries is important for the
operation of the Terminal Equipment, then this is a
very important signal for it to sample.
The Need for sampling RxOHInd
The XRT72L56 will indicate that it is currently driving
an overhead bit onto the RxSer output pin, by pulsing
the RxOHInd output pin "High". If the Terminal Equip-
ment samples this signal "High", then it should know
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 E3 Serial Mode Op-
eration is illustrated in Figure 210.
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