CHAPTER 3 CPU ARCHITECTURE
75
User’s Manual U11302EJ4V0UM
3.4.4 Short direct addressing
[Function]
The memory to be manipulated in the fixed space is directly addressed with 8-bit data in an instruction word.
The fixed space to which this addressing is applied to is the 256-byte space from FE20H to FF1FH. An internal
high-speed RAM and special-function registers (SFRs) are mapped at FE20H to FEFFH and FF00H to FF1FH,
respectively.
The SFR area (FF00H to FF1FH) where short direct addressing is applied is a part of the total SFR area. In
this area, ports which are frequently accessed in a program and compare and capture registers of the timer/event
counter are mapped and these SFRs can be manipulated with a small number of bytes and clocks.
When 8-bit immediate data is at 20H to FFH, bit 8 of an effective address is set to 0. When it is at 00H to 1FH,
bit 8 is set to 1. Refer to
[Illustration]
below.
[Operand format]
Identifier
Description
saddr
Label or immediate data indicating FE20H to FF1FH
saddrp
Label or immediate data indicating FE20H to FF1FH (even address only)
[Description example]
MOV 0FE30H, #50H; when setting saddr to FE30H and immediate data to 50H
[Illustration]
Operation code
0
0
0
1
0
0
0
1
0
0
1
1
0
0
0
0
0
1
0
1
0
0
0
0
15
0
7
0
Opcode
saddr-offset
Effective address
8
When 8-bit immediate data is 20H to FFH,
α
= 0
α
1
1
1
1
1
1
1
Short direct memory
When 8-bit immediate data is 00H to 1FH,
α
= 1
Opcode
30H (saddr-offset)
50H (immediate data)
Содержание mPD780204
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