XRT72L53 Datasheet, PDF (370/467 Pages) Exar Corporation – THREE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
XRT72L53
THREE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.8
Figure 169 presents a simple illustration of the Trans-
mit Overhead Data Input Interface block within the
XRT72L53.
FIGURE 169. SIMPLE ILLUSTRATION OF THE TRANSMIT OVERHEAD DATA INPUT INTERFACE BLOCK
TxOHFrame
TxOHEnable
TxOH
TxOHClk
TxOHIns
TTrraannsmsmitit
OOvveerrhheeaadd
DDaatataInInppuut _t
InInteterrfafacceeBBlolocckk
To Transmit E3 Framer Block
The E3, ITU-T G.832 Frame consists of 537 bytes. Of
these bytes, 530 bytes are payload bytes and the re-
maining 7 are overhead bytes. The XRT72L53 has
been designed to handle and process both the pay-
load type and overhead type bits for each E3 frame.
Within the Transmit Section within the XRT72L53, the
Transmit Payload Data Input Interface has been de-
signed to handle the payload data. Likewise, the
Transmit Overhead Input Interface has been de-
signed to handle and process the overhead bits.
The Transmit Section of the XRT72L53 generates or
processes the various overhead bits within the E3
frame, in the following manner.
The Frame Alignment Overhead Bytes (e.g., the
“FA1” and “FA2” bytes)
The "FA1" and "FA2" bytes are always internally gen-
erated by the Transmit Section of the XRT72L53.
Hence, the user cannot insert his/her value for the
"FA1" and "FA2" bytes into the Outbound DS3 data
stream, via the Transmit Overhead Data Input Inter-
face.
The Error Monitoring (EM) Overhead Byte
The EM byte is always internally generated by the
Transmit Section of the XRT72L53. Hence, the user
cannot insert his/her value for the EM byte into the
Outbound E3 data stream, via the Transmit Overhead
Data Input Interface.
The Alarm and signaling related Overhead bytes
Bytes that are used to transport the alarm conditions
can be either internally generated by the Transmit
Section within the XRT72L53, or can be externally
generated and inserted into the Outbound E3 data
stream, via the Transmit Overhead Data Input Inter-
face. The E3 frame overhead bits that fall into this cat-
egory are:
• The "MA” byte
• The "TR” byte
The Data Link Related Overhead Bits
370