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XRT79L71
PRELIMINARY
407
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
The Two Methods of Extracting out Overhead Data from the Receive Overhead Data Output Interface
Block
There are two methods that can be used to extract the overhead data from the Receive Overhead Data Output
Interface block. One "Method" is referred to as "Method 1" or the "RxOHClk" Method, and the other "method"
is referred to as "Method 2" or the "RxClk/RxOHEnable" Method. Each of these methods is described in
considerable detail below.
RxOHFrame
A8
O
Receive Overhead Data Output Interface block - Start of Frame Indi-
cator Output pin:
The exact approach that one should sample this output pin depends
from the "Receive Overhead Data Output Interface block, as described
below.
If Method 1 is used:T
he XRT79L71 will pulse this output pin "high" (for one period of RxO-
HClk) coincident to whenever the Receive Overhead Data Output Inter-
face block outputs the very first overhead bit of the most recently
received E3 frame. This output pin will be "low" at all other times. The
Receive Overhead Data Output Interface block will update this output
pin, upon the falling edge of "RxOHClk". Hence, the System-Side Termi-
nal Equipment should be designed (or configured) to sample the data, at
this pin, upon the rising edge of "RxOHClk".
If Method 2 is used:
The Receive Overhead Data Output Interface block will assert the "RxO-
HEnable" output pin (for one "RxClk" period) whenever the data, residing
on the "RxOH" output pin has become stable and is safe for "sampling".
In this case, the user should design (or configure) the System-Side Ter-
minal Equipment to sample and latch both the "RxOH" and the "RxO-
HFrame" output pins upon the falling edge of "RxClk" coincident to
whenever the "RxOHEnable" output pin is sampled "high".
RxOHEnable
B7
O
Receive Overhead Data - Enable Output Pin:
This particular output pin is only used if Method 2 is employed (see
Data Output Interface will assert this signal (e.g., pulse it "high") for one
"RxClk" period, coincident to whenever it is safe for the System-Side Ter-
minal Equipment to sample the overhead bit that is being output via the
"RxOH" output pin.
This output pin will remain "low" at all other times.
If the "Method 2" is to be used, then design (or configure) the System-
Side Terminal Equipment such that it will sample and latch the "RxOH"
output (from the XRT79L71), upon the falling edge of "RxClk" coincident
to whenever the "RxOHEnable" output pin is sampled "high".
TABLE 48: LIST AND DESCRIPTION OF THE PINS ASSOCIATED WITH THE RECEIVE OVERHEAD DATA OUTPUT
INTERFACE BLOCK
SIGNAL NAME
PIN/BALL
NUMBER
TYPE
DESCRIPTION