Short Direct Addressing - NEC UPD789026 Series User Manual

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
saddr
saddrp
[Example]
MOV FE30H, #50H; When setting saddr to FE30H and the immediate data to 50H
[Illustration]
www.DataSheet4U.com
7
15
Effective
1
Address
When 8-bit immediate data is 20H to FFH, α = 0.
When 8-bit immediate data is 00H to 1FH, α = 1.
64
CHAPTER 3 CPU ARCHITECTURE
Label or FE20H to FF1FH immediate data
Label or FE20H to FF1FH immediate data (even address only)
Instruction Code 1 1
0 0
0 1
0
OP Code
saddr-offset
8
α
1 1 1 1 1 1
User's Manual U11919EJ3V0UM00
Description
1 1 0 1 0 1
1 1 0 0 0 0
0 1 0 0 0 0
0
OP Code
30H (saddr-offset)
50H (immediate data)
Short Direct Memory