Black Box ME260A, Руководство пользователя

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14
MODULAR MODEM ELIMINATOR
2.2.5 ITU G.703 64-
KBPS
C
O
-
DIRECTIONAL
I
NTERFACE
M
ODULE
(ME266C)
The 64-kbps co-directional interface specified by ITU G.703 includes only one
transmit pair and one receive pair. To avoid the need for additional pairs, the line
signal waveform specified by G.703 for the 64-kbps co-directional interface includes
timing and framing information.
By using appropriate signal-processing circuits, it is possible to recover
the original data and clock signals from the received signal.
Thus, the receive path of the G.703 64-kbps co-directional internal module
always operates on the clock signal recovered from the received line signal. The
clock signal used by the module transmit path can be selected by means of a
jumper.
The jumper has two positions:
• INT—the transmit clock is derived from an internal oscillator.
Figure 2-3 shows the flow of timing signals with internal timing.
Figure 2-3. Flow of timing signals for INT mode.
Transmit
Circuits
Transmit
Line Signal
Receive
Line Signal
Receive
Circuits
Internal
Source
Interface
Module
(Int Mode)
Data
Data
Clock
Recovered Clock