XRT7250 Datasheet, PDF (158/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

áç
DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
new DS3 frame, but is rather driven by the Terminal
Equipment. Hence, the XRT7250 is referred to as
the Frame Slave.
2. If the user opts to configure the XRT7250 to oper-
ate in Mode 2, it is imperative that the
Tx_Start_of_Frame (or TxFrameRef) signal is syn-
chronized to the TxInClk input clock signal.
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 signals between the XRT7250
and the Terminal Equipment for DS3 Mode 2 Opera-
tion is illustrated in Figure 47.
FIGURE 47. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE XRT7250 AND THE TERMINAL EQUIP-
MENT (MODE 2 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]
TxFrameRef
TxOH_Ind
X-Bit
Payload[1]
DS3 Frame Number N
DS3 Frame Number N + 1
Note: TxOH_Ind pulses high to
denote Overhead Data
Note: X-Bit will not be processed by the
Transmit Payload Data Input Interface.
(e.g., the X-bit).
Note: TxFrame pulses high to denote
DS3 Frame Boundary.
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
R/W
0
DS3/E3*
R/W
0
Internal LOS
Enable
R/W
1
RESET
R/W
0
Interrupt
Enable Reset
R/W
1
Frame Format
R/W
0
TimRefSel[1:0]
R/W
R/W
0
1
3. Interface the XRT7250, to the Terminal Equip-
ment, as illustrated in Figure 46.
4.2.1.3 Mode 3 - The Serial/Local-Timed/
Frame-Master Mode Behavior of the XRT7250
If the XRT7250 has been configured to operate in this
mode, then the XRT7250 will function as follows.
A. Local Timing - (Uses the TxInClk signal as the
Timing Reference)
139