ATL Telecom AM2048 - Manual (Page 34)

ATL TELECOM USER GUIDE
AM2048A
65
FIGURE A2 - DTE RETURN CLOCK OPERATION
Clock
Out
Data
Out
DCE DTE
Clock
In
Data
In
Data
In
Data
Out
Data clocked out on
rising edge of the clock
Data sampled on
falling edge of clock
Data transmitted on
rising edge of clock
Clock, and data delayed
relative to DCE because
of propagation delays
Returning clock
and data further
delayed by second
set of propagation
delays
Returning clock has the same
ammount of propagation delay
returning data as the
Sampling the data on the falling edge
of the return clock avoids any problems
caused by propagation delay because
the return clock is delayed by the same
amount as the data
Clock
Out Clock
Out
64 ATL TELECOM USER GUIDE
AM2048A
FIGURE A1 - RECEIVE CLOCK INVERSION
Clock
Out
Data
Out
DCE DTE
Clock
In
Data
In
Data
In
Data
Out
Data clocked out
on rising edge of
the clock
Data sampled
on falling edge
of clock
Data
transmitted
on rising edge
of clock
Clock, and data
delayed relative to
DCE because of
propagation delays
Returning data
further delayed
by second set
of propagation
delays
Data sampled on falling edge of clock If the
total propagation delay is close to half a bit
period then the data will be sampled during
the transition, and errors will occur
Inverting the clock used to sample the recieve
data has the effect of moving the sampling
point to the opposite edge of the clock.
If erroring is occuring because propagation
delay has brought the sampling point into
the transition area then inverting the clock
should move the sampling point back to the
middle of the bit