XRT7250 Datasheet, PDF (160/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
ter 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 DS3 frame. Since the
TxOH_Ind output pin (of the XRT7250) is electrically
connected to the DS3_Overhead_Ind whenever the
XRT7250 pulses the TxOH_Ind output pin "High", it
will also be driving the DS3_Overhead_Ind input pin
(of the Terminal Equipment) "High". Whenever the
Terminal 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 DS3 Mode 3 Operation is
illustrated in Figure 49.
FIGURE 49. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 AND THE TERMINAL EQUIP-
MENT (DS3 MODE 3 OPERATION)
Terminal Equipment Signals
DS3_Clock_In
DS3_Data_Out
Tx_Start_of_Frame
DS3_Overhead_Ind
Payload[4702] Payload[4703]
X-Bit
Payload[1]
XRT7250 Transmit Payload Data I/F Signals
TxInClk
TxSer
Payload[4702] Payload[4703]
TxFrame
TxOH_Ind
X-Bit
Payload[1]
DS3 Frame Number N
Note: TxFrame pulses high to denote
DS3 Frame Boundary.
Note: TxOH_Ind pulses high to
denote Overhead Data
(e.g., the X-bit).
DS3 Frame Number N + 1
Note: X-Bit 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 "10” or “11"
as depicted below.
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
Local Loopback
R/W
0
DS3/E3*
R/W
0
Internal LOS
Enable
R/W
1
RESET
R/W
0
3. Interface the XRT7250, to the Terminal Equip-
BIT 3
BIT2
BIT 1
BIT 0
Interrupt
Enable Reset
R/W
1
Frame Format
R/W
0
TimRefSel[1:0]
R/W
R/W
1
X
ment, as illustrated in Figure 48.
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