Datasheet

Memory Expansion Registers
MC68HC812A4 Data Sheet, Rev. 7
Freescale Semiconductor 87
8.4.6 Program Page Register
Read: Anytime
Write: Anytime
When enabled (PWEN = 1), the value in this register determines which of the 256 16-Kbyte pages is
active in the program window. An access to the program page memory area ($8000 to $BFFF) forces the
contents of PPAGE to address pins ADDR15–ADDR14 and expansion address pins ADDR21–ADDR16.
At least one of the program chip-selects (CSP0 or CSP1) must be used in conjunction with this memory
expansion window. This register is used by the CALL and RTC instructions to facilitate automatic program
flow changing between pages of program memory.
8.4.7 Extra Page Register
Read: Anytime
Write: Anytime
When enabled (EWEN = 1), the value in this register determines which of the 256 1-Kbyte pages is active
in the extra window. An access to the extra page memory area forces the contents of EPAGE to address
pins ADDR15–ADDR10 and expansion address pins ADDR16–ADDR17. Address bits
ADDR21–ADDR18 are forced to one (if enabled by MXAR). Chip-select 3 set to follow the extra page
window (CS3 with CS3EP = 1) must be used in conjunction with this memory expansion window.
8.4.8 Window Definition Register
Read: Anytime
Write: Anytime
DWEN — Data Window Enable Bit
1 = Enables paging of the data space (4 Kbytes: $7000–$7FFF) via the DPAGE register
0 = Disables DPAGE
Address: $0035
Bit 7654321Bit 0
Read:
PPA21 PPA20 PPA19 PPA18 PPA17 PPA16 PPA15 PPA14
Write:
Reset:00000000
Figure 8-12. Program Page Register (PPAGE)
Address: $0036
Bit 7654321Bit 0
Read:
PEA17 PEA16 PEA15 PEA14 PEA13 PEA12 PEA11 PEA10
Write:
Reset:00000000
Figure 8-13. Extra Page Register (EPAGE)
Address: $0037
Bit 7654321Bit 0
Read:
DWENPWENEWEN00000
Write:
Reset:00000000
Figure 8-14. Window Definition Register (WINDEF)