XRT7250 Datasheet, PDF (264/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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XRT7250
DS3/E3 FRAMER IC
REV. 1.1.1
as the Frame Master and the Terminal Equipment is
referred to as the Frame Slave.
Finally, the XRT7250 will pulse its TxOH_Ind output
pin, one bit-period prior to it processing a given over-
head bit, within the outbound E3 frame. Since the
TxOH_Ind output pin (of the XRT7250) is electrically
connected to the E3_Overhead_Ind whenever the
XRT7250 pulses the TxOH_Ind output pin "High”, it
will also be driving the E3_Overhead_Ind input pin (of
the Terminal Equipment) "High". Whenever the Ter-
minal Equipment detects this pin toggling "High", it
should delay transmission of the very next DS3 frame
payload bit by one clock cycle.
The behavior of the signal between the XRT7250 and
the Terminal Equipment for E3 Mode 3 Operation is il-
lustrated in Figure 105.
FIGURE 105. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 AND THE TERMINAL EQUIP-
MENT (E3 MODE 3 OPERATION)
Terminal Equipment Signals
E3_Clock_In
E3_Data_Out
Tx_Start_of_Frame
E3_Overhead_Ind
Payload[1522] Payload[1523]
FAS , Bit 9
FAS, Bit 8
XRT7250 Transmit Payload Data I/F Signals
TxInClk
TxSer
Payload[1522] Payload[1523]
TxFrame
TxOH_Ind
FAS, Bit 9
FAS, Bit 8
E3 Frame Number N
Note: TxFrame pulses high to denote
E3 Frame Boundary.
Note: TxOH_Ind pulses high for 12
bit-periods in order to denote
Overhead Data (e.g., the FAS pattern,
the A and N bits).
E3 Frame Number N + 1
Note: FAS pattern will not be processed by the
Transmit Payload Data Input Interface.
How to configure the XRT7250 to operate in this
mode.
1. Set the NibIntf input pin "Low".
2. Set the TimRefSel[1:0] bit-fields (within the
Framer Operating Mode Register) to "01" as
depicted below.
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Local
Loopback
DS3/E3*
Internal
LOS
Enable
RESET
R/W
R/W
R/W
R/W
0
0
1
0
3. Interface the XRT7250, to the Terminal Equip-
ment, as illustrated in Figure 104.
Interrupt
Enable
Reset
Frame
Format
TimRefSel[1:0]
R/W
R/W
R/W
R/W
1
0
0
0
5.2.1.4 Mode 4 - The Nibble-Parallel/Loop-
Timed Mode Behavior of the XRT7250
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