
SiS5595 PCI System I/O Chipset
Preliminary V2.0 Nov. 2, 1998 20 Silicon Integrated Systems Corporation
following details the protocol of CKE_N, and CKE_S while entering/exiting the self-refresh
mode.
When Battery is first plugged in, CKE_S is put into HI_Z State. In fact, CKE line is driven
high by external pull up resistor at this moment. Note that the pull-up resistor should be
connected to the power supplying the SDRAM. CKE_N is also put into HI-Z State upon
power up every time. Upon power up or wake-up, the BIOS should read the STR_STS bit
stored in RTC APC 06h bit 5 to determine if it needs to alter the CKE_N, and CKE_S state.
If it is, the BIOS should program the North Bridge to drive CKE_N low, put the CKE_S into
high impedance state, and then drive the CKE_N high to exit SDRAM from self-refresh
mode. If STR_STS bit is not set, leave CKE_N and CKE_S in the high impedance state, and
have the external pull-up resistor driving CKE high.
On the other hand, CKE_N and CKE_S perform in the following way while entering into S3
State.
1) The North Bridge enables CKE_N low after the completion of emptying the write buffer.
2) The SiS5595 drives CKE_S low in 32 us later after having intercepted the Stop_Grant
special cycle on the PCI bus.
3) CKE_N stops driving CKE line in 128us to 160us later as a result of the negation of
PS_ON# to turn off the power. Starting from this point, SDRAM and the wake-up logic is
powered by the AUX3V (or AUX5V), or Vdual from Power Supply '98. The CKE_S keeps the
CKE line low from this moment. CKE_S can also be connected to DUAL_ON# of the power
supply '98.
The following example to represent routine recommended for regulating the CKE_S and
CKE_N in the S3 State for SiS5595 working with SiS530 or SiS5600/SiS620.
{Power up or resuming sequence for SiS530 or SiS5600/SiS620 core based
system}
...
If (STR_STS)
/* Drive CKE_N low with the following two steps */
Set bit 4 of reg. 6Ch in the Host to PCI config. space ;
Set bit 5 of reg. 6Ch in the Host to PCI config. space ;
/* Place CKE_S into high impedance state */
Clear bit 7 of APC Reg 04h in the SiS5595;
/* Drive CKE_N high */
Clear bit 4 of reg. 6Ch in the Host to PCI configuration space ;
If (!STR_STS)
If (the system would like to support STR)
/* Drive CKE_N high */
Set bit 5 of reg. 6Ch in the Host to PCI config. Space ;