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PMC-Sierra, Inc.
PM73488 QSE
L
PMC-980616
Issue 3
5 Gbit/s ATMSwitch Fabric Element
Released
Datasheet
86
8
TIMING DIAGRAMS
All signal names are described in
section 6.4 “Pin Descriptions” starting on page 70
. Unless otherwise indicated, all
output timing delays assume a capacitive loading of 30 pF and that the internal PLL is enabled. The use of the internal
PLL is controlled through the /PLL_BYPASS signal. It is recommended that the internal PLL remains enabled
8.1
A microprocessor cycle starts when the chip select (/CS) and either read (/RD) or write (/WR) are asserted. During
read cycles, the QSE asserts /ACK to indicate data on the data bus is valid, and during write cycles the QSE asserts /
ACK to indicate the write has finished and data can be removed from the bus. The microprocessor can terminate the
current cycle at anytime. As shown in Figure 37, the QSE stops driving the data bus and deasserts the /ACK control
line when the cycle terminates. The current cycle terminates when the chip select is deasserted, or when both read and
write are deasserted. A new cycle can start once the /ACK has been deasserted. If the cycle was terminated prema-
turely before the /ACK was asserted, then a new microprocessor cycle can start after one clock cycle.
Microprocessor Timing
NOTE: Asserting both read and write lines together while the chip select is asserted (/RD = 0, /WR = 0, and /
CS = 0) will cause the device to operate in an undefined manner.
Figure 37. Microprocessor Timing
Table 27.
Microprocessor Timing
Symbol
Parameter
Conditions
Min
Max
Unit
/ACK valid after /CS, /RD, or /
WR, whichever is low last
SE_CLK-to-output delay
/ACK
2
118
SE_CLK
cycles
ns
Tqk
/ACK
1
10
Twcy
Tvdk
Tqk
Tvk
Tvk
Thc
Thc
Tqk
Thc
Thc
Tqd
Thc
Thc
Tvd
Thd
Tva
Tva
Tha
Tva
Tha
SE_CLK
/CS
/RD
/WR
/ACK
DATA(7:0)
ADD(7:0)