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PMC-Sierra, Inc.
PM73488 QSE
L
PMC-980616
Issue 3
5 Gbit/s ATMSwitch Fabric Element
Released
Datasheet
48
4.2.2
Relation Between Local CELL_START and Data Out of the QSE
The QSE switch latency from the local CELL_START signal to the first nibble depends on the gang mode, as shown
in Figure 31. The switch latency is 8 clocks from the local CELL_START signal for all unicast gang modes, except
for unicast gang mode = 0, in which case the switch latency is 11 clocks..
The CELL_24_START signal is used as a strobe to synchronize the internal state machines of all QSEs and QRTs in
the system. When it occurs, the CELL_24_START signal must be coincident with the CELL_START signal and
should occur every 4N
th
cell time. (The signal is called CELL_24_START for legacy reasons that are no longer rele-
vant.)
4.3
The phase aligners recover a clock from the data in the QSE-to-QSE, QRT-to-QSE, and QSE-to-QRT interfaces as
shown in
Figure 32 on page 49
. The forward cell path consists of five signals, SE_D(3:0) and SE_SOC, while the
backward path consists of one signal, BP_ACK.
General Description of Phase Aligners
In the forward cell path, the phase aligners lock to the SE_SOC_IN signal that has guaranteed signal transitions. The
recovered clock is then used to sample the other signals, SE_D_IN(3:0).
In the backward path, the phase aligners lock to the BP_ACK_IN signal that has guaranteed signal transitions.
Figure 31. QSE Switch Latency
#115. #116. #117.
#0
#1
#2
#3
#115. #116. #117.
#0
End of 8 CLK Valid Window
SE_CLK
Local CELL_START
SOC Pulses
Gang Mode not = 1
SE_D_OUT
SE_SOC_OUT
Gang Mode = 1
SE_D_OUT(1)
SE_SOC_OUT(1)