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CY28378
...................... Document #: 38-07519 Rev. ** Page 11 of 21
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/M.
“N” and “M” are the values programmed in Programmable
Frequency Select N-Value Register and M-Value Register,
respectively.
“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 2.
The ratio of N and M need to be greater than “1” [N/M> 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.
RESET W ATCHDOG TIMER
Set WD(0:3) Bits = 0
INITIALIZE W ATCHDOG TIMER
Set Frequency Revert Bit
Set WD(0:3) = (# of Sec ) x 2
SET SOFTW ARE FSEL
Set SW Freq_Sel = 1
Set FS(0:4)
Wait for 6msec For
Clock Output to Ramp to
Target Frequency
Hang?
Y
W ATCHDOG TIMEOUT
N
CLEAR W D
Set WD(0:3) Bits = 0
Exit
Reset
FrequencyRevert Bit =
0
Set Frequency to
FS_HW_Latched
FrequencyRevert Bit =
1
Set Frequency to FS_SW
Set SRESET# = 0 for 6 msec
SET DIAL-A-FREQUENCY
Load M and N Registers
Set Pro_Freq_EN = 1
Figure 1. Watchdog Flowchart
Table 6. Examples of N and M Value for Different CPU Frequency Range
Frequency Ranges
Gear Constants
Fixed Value for M-Value Register
Range of N-Value Register for Different
CPU Frequency
66 – 127
47.99750
48
66 – 127
128 – 203
63.99667
40
80 – 127
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