
SiS5595 PCI System I/O Chipset
Preliminary V2.0 Nov. 2, 1998 19 Silicon Integrated Systems Corporation
Figure 3.2-4 North Bridge/5595's Timing Diagram in S3 State
Note : “stpgnt” is an internal signal. CKE_N and CKE are driven by SiS North Bridge.
S3 state (Suspend To RAM)
Disable PCI system Arbiter & AGP arbiter.
Similar to the S2 state, STPCLK# is asserted as a result of transiting the system into S3
state by writing 011(binary digit) to SLP_TYP field of register 04h in the ACPI IO space.
Having intercepted the Stop_Grant special cycle on the PCI bus, the SiS5595 will enable
and drive CKE_S low in 32us to 64 us, and then negate PS_ON# in another 128us to 160us
later.
Figure 3.2-4 North Bridge/5595's Timing Diagram in S3 State
is the timing
diagram showing the sequence happening on the SiS5595 while entering/exiting S3 State.
To provide a fast wake-up latency, it is highly recommended to place the system into the
Suspend to RAM (STR) state in S3 state. Placing the system into STR is normally achieved
through keeping the system image in the main memory (not in the hard disk). Except the
memory subsystem, and the wake-up logic, the power to the rest of the M/B components is
removed. Moreover, the memory subsystem is put into the low power state. For today's
mainstream memory like EDO or SDRAM, placing it into low power state can be performed
by programming it for self-refresh mode.
Per the SDRAM specification, it is required to keep CKE low as long as it is maintained in
self-refresh mode. There are two classes of CKE signals generated in SiS chipset. One is
CKE_N from the North Bridge, and the other is CKE_S from SiS5595. For a system which
does not support Suspend to RAM (STR), CKE can be simply connected to a pull high
resistor. To support Suspend to RAM function, an external LVT 245 is employed to generate
6 CKE signal lines to support 3 DIMM configuration. Please refer to the SiS5600/
SiS620/SiS5595 design guide or the associated application circuit for more detail. The
STPCLK#
stpgnt
CKE_S
(DUAL_ON#)
PS_ON#
PCIRST
CKE_N
CKE
32~64u
128~160u
Boot Process
clear APC reg 04h.7
Power up request
events
Set 6Ch.[5:4] of Host to PCI config. space
Set 6Ch.4 of Host to PCI config. space
enter S3