參數(shù)資料
型號: μPD789418
廠商: NEC Corp.
英文描述: 8 Bit Single Chip Microcontrollers(8位單片微控制器)
中文描述: 8位單片機微控制器(8位單片微控制器)
文件頁數(shù): 35/125頁
文件大?。?/td> 366K
代理商: ΜPD789418
CHAPTER 3 ADDRESSING
18
3.2.2 Short Direct Addressing
[Function]
The memory to be manipulated in the fixed space is directly addressed with 8-bit data in an instruction word.
This addressing is applied to the 256-byte fixed space 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 to which short direct addressing is applied (FF00H-FF1FH) constitutes only part of the overall
SFR area. 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 20H to FFH, bit 8 of an effective address is set to 0. When it is 00H to 1FH, bit
8 is set to 1. See
Illustration
, below.
[Operand format]
Identifier
Description
saddr
Label or FE20H to FF1FH immediate data
saddrp
Label or FE20H to FF1FH immediate data (even address only)
[Description 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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