XRT7250 Datasheet, PDF (168/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
0
0
1
0
3. Interface the XRT7250, to the Terminal Equip-
ment, as illustrated in Figure 54.
4.2.2 The Transmit Overhead Data Input Inter-
face
BIT 3
BIT2
BIT 1
BIT 0
1
0
1
x
Figure 56 presents a simple illustration of the Trans-
mit Overhead Data Input Interface block within the
XRT7250.
FIGURE 56. SIMPLE ILLUSTRATION OF THE TRANSMIT OVERHEAD DATA INPUT INTERFACE BLOCK
TxOHFrame
TxOHEnable
TxOH
TxOHClk
TxOHIns
TTrraannsmsmitit
OOvveerhrheeaadd
DDaatataInInppuut _t
InInteterfrafacceeBBlolocckk
To Transmit DS3 Framer Block
The DS3 Frame consists of 4760 bits. Of these bits,
4704 bits are payload bits and the remaining 56 bits
are overhead bits. The XRT7250 has been designed
to handle and process both the payload type and
overhead type bits for each DS3 frame. Within the
Transmit Section within the XRT7250, the Transmit
Payload Data Input Interface has been designed to
handle the payload data. Likewise, the Transmit
Overhead Data Input Interface has been designed to
handle and process the overhead bits.
The Transmit Section of the XRT7250 generates or
processes the various overhead bits within the DS3
frame, in the following manner.
The Frame Synchronization Overhead Bits (e.g.,
the F and M bits)
The F and M bits are always internally generated by
the Transmit Section of the XRT7250. These over-
head bits are used (by the Remote Terminal Equip-
ment) for Frame Synchronization purposes. Hence,
the user cannot insert his/her value for the F and M
bits into the outbound DS3 data stream, via the
Transmit Overhead Data Input Interface. Any attempt
to externally insert values for the “F” and “M” bits, will
be ignored by the Transmit Overhead Data Input In-
terface"High" block.
The Performance Monitoring Overhead Bits (P
and CP Bits)
The P-bits are always internally generated by the
Transmit Section of the XRT7250. The “P” bits are
used by the Remote Terminal Equipment to perform
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