Freescale Semiconductor Demonstration Board for Freescale MC9S12XHY256 Microcontroller DEMO9S12XHY256 DEMO9S12XHY256 用户手册

Freescale Semiconductor

167

Read: Anytime

Write: Anytime

These eight index bits are used to page 4KB blocks into the RAM page window located in the local (CPU
or BDM) memory map from address 0x1000 to address 0x1FFF (see

. This supports accessing

up to 1022KB of RAM (in the Global map) within the 64KB Local map. The RAM page index register is
effectively used to construct paged RAM addresses in the Local map format

.

Because RAM page 0 has the same global address as the register space, it is
possible to write to registers through the RAM space when RPAGE = 0x00.

The reset value of 0xFD ensures that there is a linear RAM space available between addresses 0x1000 and
0x3FFF out of reset.

The fixed 4K page from 0x2000–0x2FFF of RAM is equivalent to page 254 (page number 0xFE).

The fixed 4K page from 0x3000–0x3FFF of RAM is equivalent to page 255 (page number 0xFF).

The page 0xFD (reset value) contains unimplemented area in the range not
occupied by RAM if RAMSIZE is less than 12KB (Refer to

7–0

RP[7:0]

RAM Page Index Bits 7–0 — These page index bits are used to select which of the 256 RAM array pages is to
be accessed in the RAM Page Window.

Bit18

Bit0

Bit11

0

Address [11:0]

RPAGE Register [7:0]

Global Address [22:0]

Bit12

Bit19

0

Address: CPU Local Address

or BDM Local Address

0