
MOTOROLA
Chapter 3. Device Programming
3-67
Figure 3-41. Modified Memory Status Register—0xE4/0xEC
3.2.10 External Configuration Registers
When using address map A, certain configuration bits can be accessed by reading or writing
to the ports at addresses 0x8000_0092 (referred to as port 0x092), 0x8000_081C (referred
to as port 0x81C), or 0x8000_0850 (referred to as port 0x850). These external configuration
registers should only be accessed as a 1-byte quantity, even though the other bytes in the
double word are reserved.
PICR1[NO_PORT_REGS] controls access to these registers. If NO_PORT_REGS is set,
the MPC106 handles all accesses to the external configuration registers. If
NO_PORT_REGS is cleared, the MPC106 treats accesses to the external configuration
registers as PCI memory accesses. However, writes to the external configuration registers
are always shadowed in PICR1 regardless of the state of NO_PORT_REGS. For example,
if bit 1 of the data being written to port 0x092 is set, then when the configuration write
access completes on the PCI bus, the MPC106 enters little-endian mode and
PICR1[LE_MODE] is set.
See Figure 3-42 and Table 3-43 for external configuration register 1 bit settings.
Table 3-42. Bit Settings for Modified Memory Status Register—0xE4/0xEC
Bit
Name
Reset
Value
Description
31–17
HWM
All 0s
These bits indicate the address of a modified memory block or
boundary depending on the value in MOD_MEM_STATUS. The
block size is controlled by ESCR2[MOD_MEM_SIZE].
16–2
LWM
All 0s
These bits indicate the address of a modified memory block or
boundary depending on the value in MOD_MEM_STATUS. The
block size is controlled by ESCR2[MOD_MEM_SIZE].
1–0
MOD_MEM_STATUS
00
These bits encode the status of the HWM and LWM addresses.
00
Both HWM and LWM are invalid.
01
Both HWM and LWM are valid. HWM and LWM contain the
same address of a block of memory that has been modified.
10
Both HWM and LWM are valid. HWM contains the address of
a block of memory that has been modified, and LWM contains
the address of another block of memory that has been
modified.
11
Both HWM and LWM are valid. LWM contains the lower
boundary and HWM contains the upper boundary of an area
of memory that may have been modified.
31
17 16
2 1 0
HWM
LWM
MOD_MEM_STATUS