REGISTER SUMMARY
M68HC16 Z SERIES
D-20
USER’S MANUAL
External memories are purchased with guaranteed access times on speed (in nano-
seconds).
relates wait states selected by DSACK[3:0] to the memory de-
vice access time.
NOTE
assumes a system configuration that minimizes power
consumption and the number of chip-selects employed. Other ac-
cess techniques can provide the same access times with slower
memory devices, but require more chip-selects to be used and will
subsequently increase system power consumption.
Table D-15 DSACK Field Encoding
DSACK[3:0]
Clock Cycles Required
Per Access
Wait States Inserted
Per Access
0000
3
0
0001
4
1
0010
5
2
0011
6
3
0100
7
4
0101
8
5
0110
9
6
0111
10
7
1000
11
8
1001
12
9
1010
13
10
1011
14
11
1100
15
12
1101
16
13
1110
2
Fast Termination
1111
—
External DSACK
Table D-16 Memory Access Times at 16.78, 20.97, and 25.17 MHz
Speed
t
cyc
Fast Termination Access Time
0 Wait State
1 Wait State
16.78 MHz
62.5 ns
30.0 ns
95.0 ns
155.0 ns
20.97 MHz
50.0 ns
20.0 ns
70.0 ns
120.0 ns
25.17 MHz
40.0 ns
15.0 ns
55.0 ns
95.0 ns
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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