CHAPTER 5 MEMORY ACCESS CONTROL FUNCTION
User’s Manual U12688EJ4V0UM00
153
5.3.8 Refresh control function
V850E/MS1 can create a CBR (CAS-before-RAS) refresh cycle. The refresh cycle is set with the refresh control
register (RFC).
When another bus master occupies the external bus, the DRAM controller cannot occupy the external bus. In this
case, the DRAM controller sends a refresh request to the bus master by changing the REFRQ signal to active (low
level).
During the refresh interval, the address bus maintains the state it was in just before the refresh cycle.
(1) Refresh control registers 0 to 3 (RFC0 to RFC3)
These set whether refresh is enabled or disabled, and the refresh interval. The refresh interval is determined
by the following calculation formula.
Refresh interval (
µ
s) = Refresh count clock (T
RCY
)
×
Interval factor
The refresh count clock and interval factor are determined by the RENn bit and RIn bit, respectively, of the
RFCn register.
Note that n corresponds to the register number (0 to 3) of DRAM configuration registers 0 to 3 (DRC0 to
DRC3).
These registers can be read/written in 16-bit units.
0
RI
00
Address
FFFFF210H
After reset
0000H
1
RI
01
2
3
4
5
6
7
8
RCC
00
9
RCC
01
REN
0
RI
04
RI
02
RI
05
RI
03
10
11
12
13
0
0
0
0
0
0
0
RI
10
RI
11
RCC
10
RCC
11
REN
1
RI
14
RI
12
RI
15
RI
13
0
0
0
0
0
0
0
RI
20
RI
21
RCC
20
RCC
21
REN
2
RI
24
RI
22
RI
25
RI
23
0
0
0
0
0
0
0
RI
30
RI
31
RCC
30
RCC
31
REN
3
RI
34
RI
32
RI
35
RI
33
0
0
0
0
0
0
0
14
15
RFC0
FFFFF212H
0000H
RFC1
FFFFF214H
0000H
RFC2
FFFFF216H
0000H
RFC3
Bit Position
Bit Name
Function
15
RENn
Refresh Enable
Specifies whether CBR refresh is enabled or disabled.
0: Refresh disabled
1: Refresh enabled
Remark
n = 0 to 3
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