XC886/888CLM
Memory Organization
User’s Manual
3-13
V1.3, 2010-02
Memory Organization, V 1.2
3.5.2
Address Extension by Paging
Address extension is further performed at the module level by paging. With the address
extension by mapping, the XC886/888 has a 256-SFR address range. However, this is
still less than the total number of SFRs needed by the on-chip peripherals. To meet this
requirement, some peripherals have a built-in local address extension mechanism for
increasing the number of addressable SFRs. The extended address range is not directly
controlled by the CPU instruction itself, but is derived from bit field PAGE in the module
page register MOD_PAGE. Hence, the bit field PAGE must be programmed before
accessing the SFRs of the target module. Each module may contain a different number
of pages and a different number of SFRs per page, depending on the specific
requirement. Besides setting the correct RMAP bit value to select the SFR area, the user
must also ensure that a valid PAGE is selected to target the desired SFRs.
shows how a page inside the extended address range can be selected.
Figure 3-5
Address Extension by Paging
SFR0
SFR1
SFRx
…
...
PAGE 0
SFR0
SFR1
SFRy
….
..
PAGE 1
….
..
SFR0
SFR1
SFRz
…..
.
PAGE q
MOD_PAGE.PAGE
SFR Address
(from CPU)
SFR Data
(to/from CPU)
rw
Module
*