RG82845SL5YQ Datasheet, PDF (57/148 Pages) Intel Corporation – Intel® 845 Chipset: 82845 Memory Controller Hub (MCH) for SDR

Register Description
R
Bit
Description
6:4
Mode Select (SMS)—R/W. These bits select the special operational mode of the system
memory interface. The special modes are intended for initialization at power up.
000 = Post Reset state. When the MCH exits reset (power-up or otherwise), the mode select
field is cleared to “000”.
During any reset sequence, while power is applied and reset is active, the MCH asserts
all CKE signals. After internal reset is deasserted, CKE signals remain deasserted until
this field is written to a value different than “000”. On this event, all CKE signals are
asserted.
During suspend, MCH internal signal triggers system memory controller to flush pending
commands and enter all rows into Self-Refresh mode. As part of resume sequence, the
MCH will be reset ( which will clear this bit field to “000” and maintain CKE signals
deasserted). After internal reset is deasserted, CKE signals remain deasserted until this
field is written to a value different than “000”. On this event, all CKE signals are asserted.
During entry to other low power states (C3, S1), MCH internal signal triggers DRAM
controller to flush pending commands and enter all rows into Self-Refresh mode. During
exit to normal mode, MCH signal triggers DRAM controller to exit Self-Refresh and
resume normal operation without S/W involvement.
001 = NOP Command Enable. All processor cycles to system memory result in a NOP
command on the system memory interface.
010 = All Banks Pre-charge Enable. All processor cycles to system memory result in an “all
banks precharge” command on the system memory interface.
011 = Mode Register Set Enable. All processor cycles to system memory result in a “mode
register” set command on the system memory interface. Host address lines are mapped
to memory address lines to specify the command sent. Host address lines [15:3] are
mapped to SMA[12:0].
100 = Reserved
101 = Reserved
110 = CBR Refresh Enable. In this mode all processor cycles to system memory result in a
CBR cycle on the SDRAM interface
111 = Normal operation.
3:2
Reserved.
1:0
DRAM Type (DT)—RO. Used to select between supported SDRAM types.
00 = Single Data Rate (SDR) SDRAM.
01–11 = Reserved
Intel^® 82845 MCH for SDR Datasheet
57