W311 Datasheet, PDF (14/19 Pages) Silicon Laboratories – FTG for VIA™ Pro-266 DDR Chipset

W311
Table 6. Register Summary
Name
WD_TO_STATUS
WD_TIMER[4:0]
WD_PRE_SCALER
RST_EN_WD
RST_EN_FC
Description
Watchdog Timer Time-out Status bit
0 = No time-out occurs (READ); Ignore (WRITE)
1 = Time-out occurred (READ); Clear WD_TO_STATUS (WRITE)
These bits store the time-out value of the Watchdog Timer. The scale of the timer is determine by the
pre-scaler.
The timer can support a value of 150 ms to 4.8 sec when the pre-scaler is set to 150 ms. If the prescaler
is set to 2.5 sec, it can support a value from 2.5 sec to 80 sec.
When the Watchdog Timer reaches “0.” it will set the WD_TO_STATUS bit.
0 = 150 ms
1 = 2.5 sec
This bit will enable the generation of a Reset pulse when a Watchdog Timer time-out occurs.
0 = Disabled
1 = Enabled
This bit will enable the generation of a Reset pulse after a frequency change occurs.
0 = Disabled
1 = Enabled
How to program CPU output frequency?
When the programmable output frequency feature is enabled
(Pro_Freq_EN bit is set), the CPU output frequency is deter-
mined by the following equation:
Fcpu = G * (N+3)/(M+3)
“N” and “M” are the values programmed in Programmable Fre-
quency Select N-Value Register and M-Value Register, re-
spectively.
“G” stands for the PLL Gear Constant, which is determined by
the programmed value of FS[4:0] or SEL[4:0]. The value is
listed in Table 5.
The ratio of (N+3) and (M+3) need to be greater than “1”
[(N+3)/(M+3) > 1].
The following table lists set of N and M values for different
frequency output ranges.This example use a fixed value for the
M-Value Register and select the CPU output frequency by
changing the value of the N-Value Register.
Table 7. Examples of N and M Value for Different CPU Frequent Range
Frequency Ranges
50 MHz – 129 MHz
130 MHz – 248 MHz
Gear Constants
48.00741
48.00741
Fixed Value for
M-Value Register
93
45
Range of N-Value Register
for Different CPU Frequency
97 – 255
127 – 245
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