Memory Mapping Control (S12XMMCV4)
MC9S12XHY-Family Reference Manual, Rev. 1.01
164
Freescale Semiconductor
3.3.2.3
Direct Page Register (DIRECT)
Read: Anytime
Write: anytime in special modes, one time only in other modes.
This register determines the position of the 256B direct page within the memory map.It is valid for both
global and local mapping scheme.
Figure 3-9. DIRECT Address Mapping
Bits [22:16] of the global address will be formed by the GPAGE[6:0] bits in case the CPU executes a global
instruction in direct addressing mode or by the appropriate local address to the global address expansion
(refer to
Section 3.4.2.1.1, “Expansion of the Local Address Map
).
Example 3-2. This example demonstrates usage of the Direct Addressing Mode
MOVB
#0x80,DIRECT
;Set DIRECT register to 0x80. Write once only.
;Global data accesses to the range 0xXX_80XX can be direct.
;Logical data accesses to the range 0x80XX are direct.
LDY
<00
;Load the Y index register from 0x8000 (direct access).
;< operator forces direct access on some assemblers but in
;many cases assemblers are “direct page aware” and can
;automatically select direct mode.
Address: 0x0011
7
6
5
4
3
2
1
0
R
DP15
DP14
DP13
DP12
DP11
DP10
DP9
DP8
W
Reset
0
0
0
0
0
0
0
0
Figure 3-8. Direct Register (DIRECT)
Table 3-5. DIRECT Field Descriptions
Field
Description
7–0
DP[15:8]
Direct Page Index Bits 15–8 — These bits are used by the CPU when performing accesses using the direct
addressing mode. The bits from this register form bits [15:8] of the address (see
Figure 3-9
).
Bit15
Bit0
Bit7
Bit22
CPU Address [15:0]
Global Address [22:0]
Bit8
Bit16
DP [15:8]
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