Example Configuration
847
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
External Memory Interface (EMIF)
The W_SETUP and W_HOLD fields should combine to satisfy the Flash's nCE Pulse Width High
constraint, t
EHEL
, when performing back-to-back writes:
W W_HOLD > = t
EHEL
× f
EMIF_CLK
- 2
W W_HOLD > = 30 ns × 100 MHz - 2
W W_HOLD > = 1
In addition, the entire Write access length must satisfy the Flash's minimum Write Cycle Time, t
AVAV
:
W W_ W_HOLD >= t
AVAV
× f
EMIF_CLK
- 3
W W_ W_HOLD >= 90 ns × 100 MHz - 3
W W_ W_HOLD >= 6
Solving the above equations for the Write fields results in the following possible solution:
W_SETUP = 1
W_STROBE = 5
W_HOLD = 0
Adding a 10 ns (1 cycle) margin to each of the periods (excluding TA which is already at its maximum) in
this example produces the following recommended values:
W_SETUP = 2h
W_STROBE = 6h
W_HOLD = 1h
R_SETUP = 1h
R_STROBE = Bh
R_HOLD = 3h
TA = 3h
Figure 21-34. Asynchronous m Configuration Register (m = 1, 2) (CEnCFG (n = 2, 3))
31
30
29
26
25
24
1
0
0010
00
SS
EW
W_SETUP
W_STROBE
23
20
19
17
16
0110
001
0
W_STROBE
W_HOLD
R_SETUP
15
13
12
7
6
4
3
2
1
0
001
001011
011
11
01
R_SETUP
R_STROBE
R_HOLD
TA
ASIZE