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Chapter 18 Memory Mapping Control (S12XMMCV3)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

661

18.3.2.3

Global Page Index Register (GPAGE)

Read: Anytime

Write: Anytime

The global page index register is used to construct a 23 bit address in the global map format. It is only used

when the CPU is executing a global instruction (GLDAA, GLDAB, GLDD, GLDS, GLDX,

GLDY,GSTAA, GSTAB, GSTD, GSTS, GSTX, GSTY) (see CPU Block Guide). The generated global

address is the result of concatenation of the CPU local address [15:0] with the GPAGE register [22:16] (see

Figure 18-7).

CAUTION

XGATE write access to this register during an CPU access which makes use

of this register could lead to unexpected results.

Figure 18-7. GPAGE Address Mapping

Example 18-1. This example demonstrates usage of the GPAGE register

LDX

#0x5000

;Set GPAGE offset to the value of 0x5000

MOVB

#0x14, GPAGE

;Initialize GPAGE register with the value of 0x14

GLDAA

;Load Accu A from the global address 0x14_5000

Address: 0x0010

76543210

GP6

GP5

GP4

GP3

GP2

GP1

GP0

Reset

00000000

= Unimplemented or Reserved

Figure 18-6. Global Page Index Register (GPAGE)

Table 18-8. GPAGE Field Descriptions

Field

Description

6–0

GP[6:0]

Global Page Index Bits 6–0 — These page index bits are used to select which of the 128 64-kilobyte pages is

to be accessed.

Bit16

Bit 0

Bit15

Bit22

CPU Address [15:0]

GPAGE Register [6:0]

Global Address [22:0]

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