W305B
Table 6. Register Summary (continued)
Name
Description
WD_EN
0 = Stop and re-load Watchdog timer. Unlock W305B from recovery frequency mode.
1 = Enable Watchdog timer. It will start counting down after a frequency change occurs.
Note. W305B will generate system reset, re-load a recovery frequency, and lock itself into a recovery
frequency mode after a Watchdog timer time-out occurs. Under recovery frequency mode, W305B will
not respond to any attempt to change output frequency via the SMBus control bytes. System software
can unlock W305B from its recovery frequency mode by clearing the WD_EN bit.
WD_TO_STATUS
WD_TIMER[4:0]
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 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.
WD_PRE_SCALER
RST_EN_WD
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
RST_EN_FC
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
“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.
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:
The following table lists the recommended frequency output
ranges for each PLL Gear Constant and its associated Bus
Frequency Ratio so that the maximum AGP and PCI output
frequencies are less than or equal to 83.1 MHz and 41.5 MHz,
respectively.
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.
Table 7. Recommended CPU Frequency Range for Different PLL Gear Ratio
Recommended Output Frequency Range (CPU/SDRAM/AGP/PCI)
Bus Frequency Ratio
(CPU/SDRAM/AGP/PCI)
Lower Limits
(N=77, M=48)
Upper Limits
(N=106, M=39)
Gear Constants
G1 (32.00494)
G2 (48.00741)
G3 (64.00988)
66 / 100 / 66 / 33
100 / 100 / 66 / 33
50.2 / 75.8 / 50.2 / 25.1
75.3 / 75.3 / 50.2 / 25.1
83.1 / 124.7 / 83.1 / 41.5
124.6 / 124.6 / 83.1 / 41.5
133 / 133 / 66 / 33
or
133 / 100 / 66 / 33
100.4 / 100.4 / 50.2 / 25.1
or
100.4 / 75.3 / 50.2 / 25.1
166.1 / 166.1 / 83.1 / 41.5
or
166.1 / 124.5 / 83.1 / 41.5
G4 (96.01482)
200 / 200 / 66 / 33
150.6 / 150.6 / 50.2 / 25.1
249.2 / 249.2 / 83.1 / 41.5
Rev 1.0,November 20, 2006
Page 15 of 20
SPECTRALINEAR [ SPECTRALINEAR INC ]
