MC68HC812A4 Datasheet, PDF (133/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Memory Expansion and Chip-Select
Memory Expansion Registers
8.5.7 Extra Page Register
Address: $0036
Bit 7
6
5
4
3
2
1
Read:
PEA17
Write:
PEA16
PEA15
PEA14
PEA13
PEA12
PEA11
Reset: 0
0
0
0
0
0
0
Figure 8-13. Extra Page Register (EPAGE)
Read: Anytime
Write: Anytime
Bit 0
PEA10
0
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.
8.5.8 Window Definition Register
Address: $0037
Bit 7
6
5
4
3
2
1
Bit 0
Read:
DWEN PWEN EWEN
0
0
0
0
0
Write:
Reset: 0
0
0
0
0
0
0
0
Figure 8-14. Window Definition Register (WINDEF)
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
Advance Information
MOTOROLA
Memory Expansion and Chip-Select
MC68HC812A4 — Rev. 3.0
133