XRT74L73 Datasheet, PDF (461/488 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 103: LISTING AND DESCRIPTION OF THE PIN ASSOCIATED WITH THE RECEIVE OVERHEAD DATA OUTPUT
INTERFACE BLOCK
SIGNAL NAME
RxOH
RxOHClk
RxOHFrame
TYPE
Output
Output
Output
DESCRIPTION
Receive Overhead Data Output pin:
The XRT74L73 will output the overhead bits, within the incoming E3 frames, via this pin.
The Receive Overhead Data Output Interface block will output a given overhead bit, upon the
falling edge of RxOHClk. Hence, the external data link equipment should sample the data, at
this pin, upon the rising edge of RxOHClk.
The XRT74L73 will always output the E3 Overhead bits via this output pin. There are no exter-
nal input pins or register bit settings available that will disable this output pin.
Receive Overhead Data Output Interface Clock Signal:
The XRT74L73 will output the Overhead bits (within the incoming E3 frames), via the RxOH
output pin, upon the falling edge of this clock signal.
As a consequence, the user’s data link equipment should use the rising edge of this clock sig-
nal to sample the data on both the RxOH and RxOHFrame output pins.
This clock signal is always active.
Receive Overhead Data Output Interface - Start of Frame Indicator:
The XRT74L73 will drive this output pin "High" (for one period of the RxOHClk signal), when-
ever the first overhead bit within a given E3 frame is being driven onto the RxOH output pin.
Table 104 relates the number of rising clock edges was last sampled “High”) to the E3 Overhead bit that
(in the RxOHClk signal, since the RxOHFrame signal is being output via the RxOH output pin.
TABLE 104: THE RELATIONSHIP BETWEEN THE NUMBER OF RISING CLOCK EDGES IN RXOHCLK, (SINCE
RXOHFRAME WAS LAST SAMPLED "HIGH") TO THE E3 OVERHEAD BIT, THAT IS BEING OUTPUT VIA THE RXOH
OUTPUT PIN
NUMBER OF RISING CLOCK EDGES IN RXOHCLK
THE OVERHEAD BIT BEING OUTPUT BY THE
XRT74L73
0 (Clock edge is coincident with RxOHFrame being detected “High”)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
FA1 Byte - Bit 7
FA1 Byte - Bit 6
FA1 Byte - Bit 5
FA1 Byte - Bit 4
FA1 Byte - Bit 3
FA1 Byte - Bit 2
FA1 Byte - Bit 1
FA1 Byte - Bit 0
FA2 Byte - Bit 7
FA2 Byte - Bit 6
FA2 Byte - Bit 5
FA2 Byte - Bit 4
FA2 Byte - Bit 3
FA2 Byte - Bit 2
FA2 Byte - Bit 1
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