
3.0 Device Architecture and Configuration
(Continued)
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These decoded I/O zones are determined by the following seven registers: X-Bus I/O Configuration, X-Bus I/O Zone Base
Address 1/2 High and Low Byte and X-Bus I/O Size 1/2 Configuration. When a zone is enabled but is not associated with
any XCS0-3 select signal in the X-Bus Interface, the X-Bus does not respond to LPC transactions accessing that zone.
The I/O Address Map Lock bit (LOCKIOMP) in XIOCNF register enables protecting the contents of the I/O mapping by pre-
venting modifications to them that would cause access rights violation through aliasing.
Figure 7 illustrates the mapping of the User-Defined I/O zones to the host I/O space. The order between Base Address 1
and 2 is an example only and may be reversed.
3.15.3
LPC memory transactions or LPC-FWH transactions can be forwarded to the X-Bus Extension of the PC8741x device.
X-Bus Memory Configuration Register 1 defines the address space to which the device responds. The XCNF2 strap input
controls the default setting of the XMEMCNF1 register to enable booting from memories connected on the X-Bus. Two mem-
ory areas may be individually enabled: a user-defined zone and a BIOS memory zone (either BIOS-LPC, or BIOS-FWH
spaces).
To enable BIOS support, set the XCNF2 strap input to select the BIOS mode (see Section 1.4.11 on page 29 for details).
The PC8741x devices respond to LPC memory read and write transactions to/from the BIOS address spaces (see Table 28)
as long as the BIOLPCEN bit of XMEMCNF1 register is set (see Section 3.15.11 on page 83).
X-Bus Memory Range Programming
Table 28. BIOS-LPC Memory Space Definition
The PC8741x devices respond to LPC-FWH read transactions from the high memory address range (’386’ mode BIOS
range), shown in Table 28, as long as BIOFWHEN = 1 in the XMEMCNF1 register.
Memory Address Range
Description
000E 0000h - 000E FFFFh
Extended BIOS Range (Legacy)
Only when BIOEXTEN = 1 in XMEMCNF1 register
BIOS Range (Legacy)
386 mode BIOS Range.
This is the upper 256 Kbytes to 32 Mbytes of the memory
space, depending on the setting of BIOSIZE and SEL2BIOS
in XMEMCNF2 (see Section 3.15.12 on page 84).
000F 0000h - 000F FFFFh
FFFC 0000h - FFFF FFFFh
FFF8 0000h - FFFF FFFFh
FFF0 0000h - FFFF FFFFh
FFE0 0000h - FFFF FFFFh
FFC0 0000h - FFFF FFFFh
FF80 0000h - FFFF FFFFh
FF00 0000h - FFFF FFFFh
FE00 0000h - FFFF FFFFh
Figure 7. User-Defined I/O Block Mapping
Host I/O Space
FFFFh
0000h
Base Address 1 (High, Low)
Base Address 2 (High, Low)
Zone Size 1
Zone Size 1
User-Defined I/O Zone 2 (UDIZ2)
User-Defined I/O Zone 3 (UDIZ3)
User-Defined I/O Zone 0 (UDIZ0)
User-Defined I/O Zone 1 (UDIZ1)
Zone Size 2
Zone Size 2