Advanced Notebook I/O for ISA or LPC Designs
Datasheet
Rev. 0.5 (03-24-05)
Page 40
SMSC SIO10N268
DATASHEET
8.4
FWH Interface (LPC Mode Only)
The Firmware Hub (FWH) interface shares the LPC interface pins LAD[3:0] and LFRAME#. The FWH
implements a specific memory cycle for the purpose of interface for the BIOS. If enabled, the FWH cycles
in the SIO10N268 are forwarded to the X-Bus Interface. To enable FWH memory cycle decoding the
MEM_EN bit must be set to ‘1’ and the FWH_SEL bit must be set to ‘1’ in the FWH ID Select register
located at offset CR54. The default value of these bits is determined by the MEM_EN and FWH_SEL
strapping options. (See Table 8.5 - FWH Strapping Options)
The FWH supports single byte memory transactions only.
8.4.1
Enabling the FWH Interface
The LPC interface can be used to decode FWH memory cycles if enabled. To enable FWH memory cycle
decoding the MEM_EN bit must be set to ‘1’ and the FWH_SEL bit must be set to ‘1’ in the FWH ID Select
register located at offset CR54. The default value of these bits is determined by the MEM_EN and
FWH_SEL strapping options. The following table defines the FWH Strapping options.
Table 8.5 - FWH Strapping Options
NAME
OPTIONS
PIN
DESCRIPTION
1 = X-Bus Memory
Cycles Enabled
1.
MEMEN
0 = X-Bus Memory
Cycles Disabled
GP57/nDTR2
When MEMEN is asserted,
the LPC interface will decode
memory or FWH addresses
for the X-Bus. When MEMEN
is deasserted, the LPC
interface will not decode
memory or FWH addresses
1 = FWH Memory
Cycles Selected
2.
FWHSEL
0 = LPC Memory
Cycles Selected
nDTR1
Assuming X-Bus memory
cycles are enabled (MEMEN
= 1), when FWHSEL is
asserted FWH memory cycles
are decoded for the X-Bus.
When FWHSEL is
deasserted, LPC memory
cycles are decoded for the X-
Bus.
8.4.1.1
MEMEN
The MEMEN strap option determines if memory cycles are decoded for the X-Bus interface. When the
MEMEN strap option is asserted ‘1’ during VCC POR or Hard Reset, the LPC interface will decode LPC or
FWH memory cycles (depending on the FWHSEL option). When the MEMEN strap option is deasserted
‘0’ during VCC POR or Hard Reset, the LPC interface will not decode FWH or LPC memory cycles.
The affects of the MEMEN strap option can be overridden by the MEMEN bit in the FWH ID Select register
(see section CR54).
8.4.1.2
FWHSEL
The FWHSEL strap option selects whether LPC memory or FWH cycles are decoded for the X-Bus
interface, assuming the MEMEN option is asserted.