CHAPTER 5 MEMORY ACCESS CONTROL FUNCTION
User’s Manual U12688EJ4V0UM00
155
Example An example of the DRAM refresh interval and an example of setting the interval factor are shown below.
Table 5-2. Example of DRAM Refresh Interval
DRAM Capacity (bits)
Refresh Cycle (Cycles/ms)
Refresh Interval (
µ
s)
256 K
256/4
15.6
512/8
15.6
1 M
512/64
125
512/128
250
1 K/16
15.6
4 M
1 K/128
125
1 K/256
250
2 K/256
125
4 K/64
15.6
16 M
4 K/256
62.5
64 M
4 K/64
15.6
Table 5-3. Example of Interval Factor Settings
Interval Factor Value
Notes 1, 2
Specified Refresh
Interval Value (
µ
s)
Refresh Count
Clock (T
RCY
)
When
φ
= 16 MHz
When
φ
= 20 MHz
When
φ
= 33 MHz
When
φ
= 40 MHz
32/
φ
7 (14)
9 (14.4)
15 (14.5)
19 (15.2)
128/
φ
1 (8)
2 (12.8)
3 (11.6)
4 (12.8)
15.6
256/
φ
1 (12.8)
1 (7.8)
2 (12.8)
32/
φ
30 (60)
38 (60.8)
63 (61.1)
128/
φ
7 (56)
9 (57.6)
15 (58.2)
19 (60.8)
62.5
256/
φ
3 (48)
4 (51.2)
7 (54.3)
9 (57.6)
32/
φ
128/
φ
15 (120)
19 (121.6)
32 (124.1)
39 (124.8)
125
256/
φ
7 (112)
9 (115.2)
16 (124.1)
19 (121.6)
32/
φ
128/
φ
31 (248)
38 (243.2)
64 (248.2)
250
256/
φ
15 (240)
19 (243.2)
32 (248.2)
39 (249.6)
Notes 1. The interval factor is set by bits RIn0 to RIn5 of the RFCn register (n = 0 to 3).
2. The values in parentheses are the calculated value (
µ
s) for the refresh interval.
Refresh Interval (
µ
s) = Refresh count clock (T
RCY
)
×
Interval factor
Remark
φ
: Internal system clock frequency
Содержание V850E/MS1 UPD703100
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