CY28342
Rev 1.0, November 20, 2006 Page 11 of 21
System Self-recovery Clock Management
This feature is designed to allow the system designer to
change frequency while the system is running and reboot the
operation of the system in case of a hang up due to the
frequency change.
When the system sends an SMBus command requesting
a frequency change through byte 4 or through bytes 13 and
14, it must have previously sent a command selecting which
time-out stamp the Watchdog must perform to byte 12, or the
system self-recovery feature will not be applicable. Conse-
quently this device will change frequency, and then the
Watchdog timer starts timing. Meanwhile, the system BIOS is
running its operation with the new frequency. If this device
receives a new SMBus command to clear the bits originally
programmed in byte 12, bits(3:0) (reprogram to 0000) before
Watchdog times out, this device will keep operating in its
normal condition with the new selected frequency. If the
Watchdog times out the first time before the new SMBus repro-
grams byte 12, bits(3:0) to (0000), then this device will send
a low system reset pulse, on SRESET# (see byte 12, bit 7),
and changes the Watchdog alarm (byte 12, bit 4) status to “1”
then restarts the Watchdog timer. If the Watchdog times out
a second time, this device will send another low pulse on
SRESET#, will relatch original hardware strapping frequency
(or second-to-last software-selected frequency, see byte 12,
bit6) selection, set Watchdog alarm bit (byte 12, bit4) to “1,”
then start the Watchdog timer again. The above-described
sequence will keep repeating until the BIOS clears the SMBus
byte 12 bits(3:0). Once the BIOS sets byte 12 bits(3:0) = 0000,
the Watchdog timer is turned off and the Watchdog alarm bit
(byte 12, bit 4) is reset to “0.”
System running with
o rig in a lly s e le c te d
frequency via
hardware strapping.
Receive Frequency
Change Request via
SM B us Byte 4 or Via Dial-
a-frequency?
Start internal watch dog tim er.
W atch D og tim e out?
Turn off watch dog tim er.
Keep new frequency setting. Set W D alarm
bit (byte 12, bit4) to ''0'
1) Send another 3m S low pulse on SRES ET
2) Relatch original hardware strapping selection
for return to original frequency settings.
3) Set W D Alarm bit (byte 12, Bit4) to "1"
4 ) S ta rt W D tim e r
Frequency will change but System Self
Recovery not applicable (no tim e stam p
selected and byte 12, bit(3:0) is still =
"0000"
No
No
Yes
No
No
Yes
SM B us byte 12 tim e
out stam p disabled?
Is SMBus Byte 9, tim e out
stam p enabled - (byte 12, bit
(3:0) 0000)?
Change to a new
frequency
Yes
1) Send SRES ET
pulse
2) Set W D bit
(byte12, bit4) to '1'
3) Start W D tim er
Yes
W atch D og tim e out?
No
Yes
SMBus byte 9 tim e out
stam p disabled, Byte
12, bit(3:0) = (0000)?
Yes
No
Table 11.CPU Clock Current Select Function
Mult0 Board Target Trace/Term Z Reference R, Iref – VDD (3*Rr) Output Current Voh @ Z
0 50 Ohms (not used) Rr = 221 1%, Iref = 5.00mA IOH = 4*Iref 1.0V @ 50
1 50 Ohms Rr = 475 1%, Iref = 2.32mA IOH = 6*Iref 0.7V @ 50
Table 12.Group Timing Relationship and Tolerances
Offset Tolerance(or Range) Conditions Notes
CPU to SDCLK Typical 0 ns ±2 ns CPU leads Note 6
CPU to AGP Typical 2 ns 1-4ns CPU leads Note 6
CPU to ZCLK Typical 2 ns 1-4ns CPU leads Note 6
CPU to PCI Typical 2 ns 1-4ns CPU leads Note 6