NEC 78K/0 Series - Manual (Page 27)

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CHAPTER 3 ADDRESSING
User's Manual U12326EJ4V0UM
15 0
Short direct memory
Effective
address
1 1 1 1 1 1 1
8 7
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.
3.2.4 Short direct addressing
[Function]
The memory to be manipulated in the fixed space is directly addressed with 8-bit data in an instruction word.
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 (FF00H to FF1FH) where short direct addressing is applied is a part of the entire SFR area.
Ports that are frequently accessed in a program, a compare register of the timer/event counter and a capture
register of the timer/event counter are mapped in the area FF00H through FF1FH, 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] 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
[Illustration]
Instruction code 0 0 0 1 0 0 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)