Datasheet

Memory Expansion and Chip-Select
MC68HC812A4 Data Sheet, Rev. 7
90 Freescale Semiconductor
CS0E — Chip-Select 0 Enable Bit
CS1, CS2, and CS3 have higher precedence and can override CS0 for portions of this space.
1 = Enables this chip-select which covers a 512-byte space following the register space
($x200–$x3FF or $xA00–$xBFF)
0 = Disables this chip-select
8.6.2 Chip-Select Control Register 1
Read: Anytime
Write: Anytime
CSP1FL — Program Chip-Select 1 Covers Full Map
1 = If CSPA21 is cleared, chip-select program 1 covers the entire memory map. If CSPA21 is set,
this bit has no meaning or effect.
0 = If CSPA21 is cleared, chip-select program 1 covers half the map, $8000 to $FFFF. If CSPA21
is set, this bit has no meaning or effect.
CSPA21 — Program Chip-Select Split Based on ADDR21
Setting this bit allows two 2-Mbyte memories to make up the 4-Mbyte addressable program space.
Since ADDR21 is always one in the unpaged $C000 to $FFFF space, CSP0 is active in this space.
1 = Program chip-selects are both active (if enabled) for space $8000 to $FFFF; CSP0 if ADDR21
is set and CSP1 if ADDR21 is cleared.
0 = CSP0 and CSP1 do not rely on ADDR21.
CSDHF — Data Chip-Select Covers Half the Map
1 = Data chip-select covers half the memory map ($0000 to $7FFF) including the optional data page
window ($7000 to $7FFF).
0 = Data chip-select covers only $7000 to $7FFF (the optional data page window).
CS3EP — Chip-Select 3 Follows Extra Page
1 = Chip-select 3 follows accesses to the 1-Kbyte extra page ($0400 to $07FF or $0000 to $03FF).
Any accesses to this window cause the chip-select to go active. (EWEN must be set to 1.)
0 = Chip-select 3 includes only accesses to a 128-byte space following the register space.
Address: $003D
Bit 7654321Bit 0
Read: 0
CSP1FL CSPA21 CSDHF CS3EP
000
Write:
Reset:00000000
= Unimplemented
Figure 8-17. Chip-Select Control Register 1 (CSCTL1)