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W_STROBE w
t
WP
(m)
t
cyc
* 1
W_SETUP ) W_STROBE w max
ǒ
t
AW
(m)
t
cyc
,
t
DS
(m)
t
cyc
Ǔ
* 1
W_HOLD w max
ǒ
t
WR
(m)
t
cyc
,
t
DH
(m)
t
cyc
Ǔ
* 1
W_SETUP ) W_STROBE ) W_HOLD w
t
WC
(m)
t
cyc
* 3
t
WC
(m)
Strobe
Setup Hold
t
WR
(m)
t
WP
(m)
t
AW
(m)
t
DS
(m)
t
DH
(m)
EM_CS
EM_A[21:0]
EM_BA[1:0]
EM_WE
EM_D[15:0]
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Use Cases
Figure 13 shows an asynchronous write access and describes how the EMIF and ASRAM AC timing
requirements work together to define values for W_SETUP, W_STROBE, and W_HOLD.
From Figure 13, the following equations may be derived. t
cyc
is the period at which the EMIF operates. The
W_SETUP, W_STROBE, and W_HOLD fields are programmed in terms of EMIF cycles where as the data
sheet specifications are typically given is nano seconds. This is explains the presence of t
cyc
in the
denominator of the following equations. A minus 1 is included in the equations because each field in
ACFGn is programmed in terms of EMIF clock cycles, minus 1 cycle. For example, W_SETUP is equal to
W_SETUP width in EMIF clock cycles minus 1 cycle.
Figure 13. Timing Waveform of an ASRAM Write
33
SPRUEQ7C–February 2010 Asynchronous External Memory Interface (EMIF)
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