XRT74L73 Datasheet, PDF (392/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
C. Delineation of Outbound DS3 frames (Frame
Master Mode)
The Transmit Section of the XRT74L73 will use the
TxInClk signal as its timing reference, and will initiate
E3 frame generation, asynchronously with respect to
any externally applied signal. The XRT74L73 will
pulse its TxFrame output pin "High" whenever its it
processing the very last bit-field within a given E3
frame.
D. Sampling of payload data, from the Terminal
Equipment
In Mode 3, the XRT74L73 will sample the data, at the
TxSer input pin, on the rising edge of TxInClk.
Interfacing the Transmit Payload Data Input Inter-
face block of the XRT74L73 to the Terminal Equip-
ment for Mode 3 Operation
Figure 168 presents an illustration of the Transmit
Payload Data Input Interface block (within the
XRT74L73) being interfaced to the Terminal Equip-
ment, for Mode 3 operation.
FIGURE 168. THE TERMINAL EQUIPMENT BEING INTERFACED TO THE TRANSMIT PAYLOAD DATA INPUT INTERFACE
BLOCK OF THE XRT74L73 FOR MODE 3 (SERIAL/LOCAL-TIMED/FRAME-MASTER) OPERATION
34.368MHz
Clock Source
E3_Clock_In
E3_Data_Out
Tx_Start_of_Frame
E3_Overhead_Ind
TxInClk
TxSer
TxFrameRef
TxOH_Ind
NibInt
Terminal Equipment
XRT74L73 E3 Framer
Mode 3 Operation of the Terminal Equipment
In Figure 168 , both the Terminal Equipment and the
XRT74L73 are driven by an external 34.368 MHz
clock signal. This clock signal is connected to the
E3_Clock_In input of the Terminal Equipment and the
TxInClk input pin of the XRT74L73.
The Terminal Equipment will serially output the pay-
load data on its E3_Data_Out output pin, upon the
rising edge of the signal at the E3_Clock_In input pin.
Similarly, the XRT74L73 will latch the data, residing
on the TxSer input pin, on the rising edge of TxInClk.
The XRT74L73 will pulse the TxFrame output pin
"High" for one bit-period, coincident while it is pro-
cessing the last bit-field within a given Outbound E3
frame. The Terminal Equipment is expected to moni-
tor the TxFrame signal (from the XRT74L73) and to
place the first bit, within the very next Outbound E3
frame on the TxSer input pin.
NOTE: In this case, the XRT74L73 dictates exactly when
the very next E3 frame will be generated. The Terminal
Equipment is expected to respond appropriately by provid-
ing the XRT74L73 with the first bit of the new E3 frame,
upon demand. Hence, in this mode, the XRT74L73 is
referred to as the Frame Master and the Terminal Equip-
ment is referred to as the Frame Slave.
Finally, the XRT74L73 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 XRT74L73 is electrically
connected to the E3_Overhead_Ind whenever the
XRT74L73 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.
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