CY28324 Cypress Semiconductor, CY28324 Datasheet - Page 16

• Manufacturer Part Number: CY28324
• Description: FTG for Intel Pentium 4 CPU and Chipsets
• Manufacturer: Cypress Semiconductor

Program the 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.
Table 5. Examples of N and M Value for Different CPU Frequency Range
Document #: 38-07002 Rev. *A
Register Summary(continued)
WD_TO_STATUS
WD_TIMER[4:0]
WD_PRE_SCALER
RST_EN_WD
RST_EN_FC
Frequency Ranges
130 MHz–248 MHz
50 MHz–129 MHz
Name
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
prescaler.
The timer can support a value of 150 ms to 4.8 sec when the prescaler 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
Gear Constants
48.00741
48.00741
PRELIMINARY
M-Value Register
Fixed Value for
93
45
“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 4.
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.
Description
for Different CPU Frequency
Range of N-Value Register
127–245
97–255
CY28324
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