XR72L52 Datasheet, PDF (443/480 Pages) Exar Corporation – TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
FIGURE 190. THE RECEIVE OVERHEAD OUTPUT INTERFACE BLOCK
RxOHFrame
RxOH
RxOHClk
RxOHEnable
Receive
Overhead Output
Interface Block
XRT72L52
REV. 1.0.1
From Receive
E3 Framer Block
The E3, ITU-T G.832 frame consists of 537 bytes. Of these bytes, 530 bytes are payload bits and the remain-
ing 7 bytes are overhead bytes. The XRT72L52 has been designed to handle and process both the payload
type and overhead type bytes for each E3 frame.
Within the Receive Section of the XRT72L52, the Receive Payload Data Output Interface block has been de-
signed to handle the payload bits. Likewise, the Receive Overhead Data Output Interface block has been de-
signed to handle and process the overhead bits.
The Receive Overhead Data Output Interface block unconditionally outputs the contents of all overhead bits.
The XRT72L52 does not offer the user a means to shut off this transmission of data. However, the Receive
Overhead Output Interface block does provide the user with the appropriate output signals for external Data
Link Layer equipment to sample and process these overhead bits, via the following two methods.
• Method 1- Using the RxOHClk clock signal.
• Method 2 - Using the RxClk and RxOHEnable output signals.
Each of these methods are described below.
6.3.4.1 Method 1 - Using the RxOHClk Clock signal
The Receive Overhead Data Output Interface block consists of four (4) signals. Of these four signals, the fol-
lowing three signals are to be used when sampling the E3 overhead bits via Method 1.
• RxOH
• RxOHClk
• RxOHFrame
Each of these signals are listed and described below in Table 84.
Interfacing the Receive Overhead Data Output Interface block to the Terminal Equipment (Method 1)
Figure 191 illustrates how one should interface the Receive Overhead Data Output Interface block to the Ter-
minal Equipment when using Method 1, to sample and process the overhead bits from the Inbound E3 data
stream.
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