1 refresh clock interval register (rfscir), Figure 152. refresh clock interval register (rfsc – Intel 386 User Manual
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15-7
REFRESH CONTROL UNIT
15.4.1 Refresh Clock Interval Register (RFSCIR)
Use RFSCIR to program the interval timer unit’s 10-bit down counter. The refresh counter value
is a function of DRAM specifications and processor frequency as follows:
,
where X = 128 or the # of DRAM rows, whichever is greater.
The DRAM refresh period is the time required to refresh all rows in the DRAM device.
NOTE
Because the lower seven address bits come from a linear-feedback shift
register, which generates all address bit combinations in a nonsequential order,
X in the equation above must never be less than 128 to ensure proper refresh of
all the rows in a DRAM device that has less than 128 rows.
Figure 15-2. Refresh Clock Interval Register (RFSCIR)
Refresh Clock Interval
RFSCIR
(read/write)
Expanded Addr:
ISA Addr:
Reset State:
F4A2H
—
0000H
15
8
—
—
—
—
—
—
RC9
RC8
7
0
RC7
RC6
RC5
RC4
RC3
RC2
RC1
RC0
Bit
Number
Bit
Mnemonic
Function
15–10
—
Reserved. These bits are undefined; for compatibility with future devices,
do not modify these bits.
9–0
RC9:0
Refresh Counter Value:
Write the counter value to these ten bits. The interval counter counts
down from this value. When the interval counter reaches one, the control
unit initiates a refresh request (provided it does not have a request
pending). The counter value is a function of DRAM specifications and
processor frequency (see the equation above).
counter value
DRAM refresh period (
µ
s) processor
clock
(MHz)
×
X
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