XRT74L74 Datasheet, PDF (201/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
XRT74L74
REV. P1.1.1
.
FIGURE 52. BEHAVIOR OF THE TERMINAL INTERFACE SIGNALS BETWEEN THE TRANSMIT PAYLOAD DATA INPUT
INTERFACE BLOCK OF THE XRT74L74 AND THE TERMINAL EQUIPMENT (FOR MODE 1 OPERATION)
Terminal Equipment Signals
DS3_Clock_In
DS3_Data_Out
Tx_Start_of_Frame
DS3_Overhead_Ind
Payload[4702] Payload[4703]
X-Bit
Payload[0]
XRT72L5x Transmit Payload Data I/F Signals
RxOutClk
TxSer
Payload[4702] Payload[4703]
TxFrame
TxOH_Ind
X-Bit
Payload[0]
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 XRT74L74 into the Serial/
Loop-Timed/Non-Overhead Interface Mode
1. Set the NibIntf input pin "Low".
2. Set the TimRefSel[1:0] bit fields (within the
Framer Operating Mode Register) to "00", as
illustrated 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*
R/W
R/W
0
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
0
3. Interface the XRT74L74, to the Terminal Equip-
ment, as illustrated in Figure 51.
NOTE: The XRT74L74 Framer IC cannot support the
Framer Local Loop-back Mode of operation, when operat-
ing in the Loop-Timing Mode. The XRT74L74 Framer IC
must be configured into any of the following modes, prior to
configuring the Framer Local Loop-back Mode.
• Mode 2 - Serial/Local-Timed/Frame-Slave Mode.
• Mode 3 - Serial/Local-Timed/Frame-Master Mode.
• Mode 5 - Nibble-Parallel/Local-Timed/Frame-Slave
Mode.
• Mode 6 - Nibble-Parallel/Local-Timed/Frame-Mas-
ter Mode.
NOTE: For more detailed information on Framer Local
Loop-back Mode of operation, please see the loop-back
section.
5.2.1.2 Mode 2 - The Serial/Local-Timed/
Frame-Slave Mode Behavior of the XRT74L74
If the XRT74L74 has been configured to operate in
this mode, then the XRT74L74 will function as fol-
lows.
199