
2-24
PRELIMINARY
System Register Set
Advanci ng the S tandar ds
2.4.4
M II Configuration
Registers
The M II configuration registers are used to
enable features in the M II CPU. These registers
assign non-cached memory areas, set up SMM,
provide CPU identification information and
control various features such as cache write
policy, and bus locking control. There are four
groups of registers within the M II configura-
tion register set:
7 Configuration Control Registers (CCRx)
8 Address Region Registers (ARRx)
8 Region Control Registers (RCRx)
Access to the configuration registers is achieved
by writing the register index number for the
configuration register to I/O port 22h. I/O port
23h is then used for data transfer.
Each I/O port 23h data transfer must be pre-
ceded by a valid I/O port 22h register index
selection. Otherwise, the current 22h, and the
second and later I/O port 23h operations com-
municate through the I/O port to produce
external I/O cycles. All reads from I/O port 22h
produce external I/O cycles. Accesses that hit
within the on-chip configuration registers do
not generate external I/O cycles.
After reset, configuration registers with indexes
C0-CFh and FC-FFh are accessible. To prevent
potential conflicts with other devices which
may use ports 22 and 23h to access their regis-
ters, the remaining registers (indexes D0-FBh)
are accessible only if the MAPEN(3-0) bits in
CCR3 are set to 1h. See Figure 2-16 (Page
2-29) for more information on the
MAPEN(3-0) bit locations.
If MAPEN[3-0] = 1h, any access to indexes in
the range 00-FFh will not create external I/O
bus cycles. Registers with indexes C0-CFh,
FC- FFh are accessible regardless of the state of
MAPEN[3 -0]. If the register index number is
outside the C0 -CFh or FC-FFh ranges, and
MAPEN[3 -0] are set to 0h, external I/O bus
cycles occur. Table 2-11 (Page 2-25) lists the
MAPEN[3-0] values required to access each M
II configuration register. All bits in the config-
uration registers are initialized to zero following
reset unless specified otherwise.
2.4.4.1
Configuration Control
Registers
(CCR0 - CCR6) control several functions,
including non-cacheable memory, write-back
regions, and SMM features. A list of the config-
uration registers is listed in Table 2-11 (Page
2-25). The configuration registers are described
in greater detail in the following pages.