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10
CHAPTER 2 MEMORY SPACE
Figure 2.2-3 Example of Saving Data in Stack Area
Figure 2.2-4 Example of Returning Data from Stack Area
■ Direct Area
The direct area in the F
2
MC-8FX CPU is located at the lower side of the memory space or the 1152 bytes
from 0000
H
to 047F
H
and is mainly accessed by direct addressing and bit direct addressing. The area that
can be used at a time by direct addressing and bit direct addressing is 256 bytes. 128 bytes of 0000
H
to
007F
H
can be used at any time as a direct area. 0080
H
to 047F
H
is a direct bank of 128 bytes × 8 and can
use one direct bank as a direct area by setting the direct bank pointer (DP). Conversion from the operand
address of direct addressing and bit direct addressing to the real address is done by the conversion rule
shown in Table 2.2-1 by using DP.
Access to it is obtained by the 2-byte instruction.
The I/O control registers and part of RAM that are frequently accessed are arranged in this direct area.
PUSHWA
SP 67H SP 67H
CDH
ABCDH
ABH
Before execution
MEMORY
1233
H
ABCDH
1235H
1234H
1233H
1232H
1235H
1234H
1233H
1232H
1235H
After execution
MEMORY
A
A
SP SP 567AH
IX IX FEDCH
DCH DCH
FEH FEH
5678H 567BH
567AH
5678H
5679H
567BH
567AH
5678H
5679H
XXXXH
Before execution MEMORY
After execution
MEMORY
POPW IX
Table 2.2-1 Conversion Rule for Actual Address of Direct Addressing and Bit Direct
Addressing
Operand address Direct bank pointer (DP) Actual address
00
H
to 7F
H
0000
H
to 007F
H
80
H
to FF
H
000
0080
H
to 00FF
H
001
0100
H
to 017F
H
010
0180
H
to 01FF
H
011
0200
H
to 027F
H
100
0280
H
to 02FF
H
101
0300
H
to 037F
H
110
0380
H
to 03FF
H
111
0400
H
to 047F
H