MC68HC812A4 Datasheet, PDF (127/342 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
Generation of Chip-Selects
extra space consists of four, 1-Kbyte pages making 4 Kbytes of
addressable memory.
If memory is increased to the maximum in this example, the program
space will consist of 4 Mbytes of addressable space with 256 16-Kbyte
pages and page $FF always available. The data space will be 1 Mbyte
of addressable space with 256 4-Kbyte pages and pages $F0 to $F6
mirrored to the $0000 to $6FFF space. The extra space will be 256
Kbytes of addressable space in 256 1-Kbyte pages.
$0000
$1000
$2000
INTERNAL SPACE
REGISTERS &
RAM & CS[3:0]
EEPROM
$3000
$4000
$5000
$6000
$7000
$8000
$9000
$A000
$B000
$C000
EXTERNAL SPACE
0
1
2
PAGE 3
CHIP-SELECT 3: (CS3)
$0400 TO $07FF
DATA CHIP-SELECT: (CSD)
$0000 TO $7FFF
DATA WINDOW: $7000 to $7FFF
NOTE 1
xE
PAGE xF
xD
xC
x4
xB
xA
x9
x8
x5
x7
x6
x5
x6
x4
x3
x2
x1
NOTE 1: Some 4-Kbyte blocks of phys-
ical external data memory can be se-
lected by an access to $0000–$6FFF in
x0
the 64-Kbyte map or as pages 0
through 6 in the data window. On-chip
registers, EEPROM, and EPAGE have
higher priority than CSD.
0
1
2
3
4
5
6
PAGE 7
NOTE 2: The last page of physical pro-
gram memory can be selected by an
access to $C000–$FFFF in the
64-Kbyte map or as page 7 in the pro-
gram window.
$D000
$E000
$F000
$FFFF
VECTORS
NOTE 2
$FFC0–$FFFF
PROGRAM CHIP-SELECT 0: (CSP0)
$8000 TO $FFFF
PROGRAM PAGES: $8000 to $BFFF
Figure 8-2. Memory Expansion and Chip-Select Example
Advance Information
MOTOROLA
Memory Expansion and Chip-Select
MC68HC812A4 — Rev. 3.0
127