CHAPTER 3 CPU ARCHITECTURE
User's Manual U11919EJ3V0UM00
64
3.4.2 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 where this addressing is applied to is the 256-byte space FE20H to FF1FH. An internal high-
speed RAM and a special function register (SFR) 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 all SFR areas. In this
area, ports which are frequently accessed in a program and a compare register 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. See [Illustration].
[Operand format]
Identifier
Description
saddr
Label or FE20H to FF1FH immediate data
saddrp
Label or FE20H to FF1FH immediate data (even address only)
[Example]
MOV FE30H, #50H; When setting saddr to FE30H and the immediate data to 50H
Instruction Code
1
1
1
1
0
1
0
1
OP Code
0
0
1
1
0
0
0
0
30H (saddr-offset)
0
1
0
1
0
0
0
0
50H (immediate data)
[Illustration]
15
0
Short Direct Memory
Effective
Address
1
1
1
1
1
1
1
8
0
7
OP Code
saddr-offset
α
When 8-bit immediate data is 20H to FFH,
α
= 0.
When 8-bit immediate data is 00H to 1FH,
α
= 1.
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