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XRT79L71
PRELIMINARY
565
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.
6.3.6.1
Method 1 - Operating the Receive Overhead Data Output Interface block using The
"RxOHClk" Method
This particular method is referred to as the "RxOHClk" method for the following reasons.
RxOHFrame
A8
O
Receive Overhead Data Output Interface block - Start of Frame Indica-
tor Output pin:
The way that this output pin is sampled depends upon whether "Method 1"
for extracting data from the "Receive Overhead Data Output Interface block.
If Method 1 is used:
The XRT79L71 will pulse this output pin "high" (for one period of RxOHClk)
coincident to whenever the Receive Overhead Data Output Interface 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 Terminal 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 Terminal
Equipment to sample and latch both the "RxOH" and the "RxOHFrame" out-
put pins upon the falling edge of "RxClk" coincident to whenever the "RxO-
HEnable" 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
Interface will assert this signal (e.g., pulse it "high") for one "RxClk" period,
coincident to whenever it is safe for the System-Side Terminal 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 "Method 2" is to be used, then design (or configure) the System-Side Ter-
minal 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 70: LIST AND DESCRIPTION OF THE PINS ASSOCIATED WITH THE RECEIVE OVERHEAD DATA OUTPUT
INTERFACE BLOCK
NAME
PIN/BALL
NUMBER
TYPE
DESCRIPTION