cy28325-3 Cypress Semiconductor Corporation., cy28325-3 Datasheet - Page 13

• Manufacturer Part Number: cy28325-3
• Description: Ftg For Via Pentium 4 Chipsets
• Manufacturer: Cypress Semiconductor Corporation.

Document #: 38-07590 Rev. *.*
Table 5. Register Summary (continued).
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
Frequency Select N-Value Register and M-Value Register,
respectively.
FS_Override
CPU_FSEL_N,
CPU_FSEL_M
ROCV_FREQ_SEL
ROCV_FREQ_N[7:0],
ROCV_FREQ_M[6:0]
WD_EN
WD_TO_STATUS
WD_TIMER[4:0]
WD_PRE_SCALER
RST_EN_WD
RST_EN_FC
Name
When Pro_Freq_EN is cleared or disabled
0 = Select operating frequency by FS input pins (default).
1 = Select operating frequency by SEL bits in SMBus control bytes.
When Pro_Freq_EN is set or enabled
0 = Frequency output ratio between CPU and other frequency groups and the PLL Gear Constant are
based on the latched value of FS input pins (default).
1 = Frequency output ratio between CPU and other frequency groups and the PLL Gear Constant are
based on the programmed value of SEL bits in SMBus control bytes.
When Prog_Freq_EN is set or enabled, the values programmed in CPU_FSEL_N[7:0] and
CPU_FSEL_M[6:0] determines the CPU output frequency. The new frequency will start to load when-
ever there is an update to either CPU_FSEL_N[7:0] or CPU_FSEL_M[6:0]. Therefore, it is recommend-
ed to use Word or Block Write to update both registers within the same SMBus bus operation. The
setting of FS_Override bit determines the frequency ratio for CPU, AGP and PIC. When FS_Override
is cleared or disabled, the frequency ratio follows the latched value of the FS input pins. When
FS_Override is set or enabled, the frequency ratio follows the programmed value of SEL bits in SMBus
control bytes.
ROCV_FREQ_SEL determines the source of the recover frequency when a Watchdog timer time-out
occurs. The clock generator will automatically switch to the recovery CPU frequency based on the
selection on ROCV_FREQ_SEL.
0 = From latched FS[4:0]
1 = From the settings of ROCV_FREQ_N[7:0] & ROCV_FREQ_M[6:0].
When ROCV_FREQ_SEL is set, the values programmed in ROCV_FREQ_N[7:0] and
ROCV_FREQ_M[6:0] will be used to determine the recovery CPU output frequency when a Watchdog
Timer time-out occurs. The setting of FS_Override bit determines the frequency ratio for CPU, AGP
and PIC. When it is cleared, the same frequency ratio stated in the Latched FS[4:0] register will be
used. When it is set, the frequency ratio stated in the SEL[4:0] register will be used. The new frequency
will start to load whenever there is an update to either ROCV_FREQ_N[7:0] and ROCV_FREQ_M[6:0].
Therefore, it is recommended to use Word or Block Write to update both registers within the same
SMBus bus operation.
0 = Stop and reload Watchdog Timer.
1 = Enable Watchdog Timer. It will start counting down after a frequency change occurs.
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 pre-scaler is set to 150 ms. If
the pre-scaler 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
“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 6.
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
CY28325-3
Page 13 of 19
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