XRT74L73 Datasheet, PDF (269/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
TABLE 61: LISTING AND DESCRIPTION OF THE PIN ASSOCIATED WITH THE RECEIVE PAYLOAD DATA OUTPUT
INTERFACE BLOCK
SIGNAL NAME TYPE
DESCRIPTION
RxFrame
Output Receive Start of Frame Output Indicator:
The exact behavior of this pin, depends upon whether the XRT74L73 has been configured to
operate in the Serial Mode or the Nibble-Parallel Mode.
Serial Mode Operation:
The Receive Section of the XRT74L73 will pulse this output pin "High" (for one bit period) when
the Receive Payload Data Output Interface block is driving the very first bit of a given DS3 frame,
onto the RxSer output pin.
Nibble-Parallel Mode Operation:
The Receive Section of the XRT74L73 will pulse this output pin "High" (for one nibble period),
when the Receive Payload Data Output Interface is driving the very first nibble of a given DS3
frame, onto the RxNib[2:0] output pins.
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 XRT74L73
If the XRT74L73 has been configured to operate in
the Serial mode, then the XRT74L73 will behave as
follows.
Payload Data Output
The XRT74L73 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 XRT74L73 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 XRT74L73 to the Receive Terminal
Equipment
Figure 100 presents a simple illustration as how the
user should interface the XRT74L73 to that terminal
equipment which processes Receive Direction pay-
load data.
270