Short Direct Addressing - NEC PD789860 User Manual

4.4.2 Short direct addressing

[Function]
The memory to be manipulated in the fixed space is directly addressed with the 8-bit data in an instruction word.
The fixed space where this addressing is applied is the 256-byte space FE20H to FF1FH. An internal high-
speed RAM is mapped at FE20H to FEFFH and the special function registers (SFR) are mapped at FF00H to
FF1FH.
The SFR area where short direct addressing is applied (FF00H to FF1FH) is a part of the total SFR area. In this
area, ports which are frequently accessed in a program and a compare register of the timer 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 cleared to 0. When it is at 00H to
1FH, bit 8 is set to 1. See [Illustration] below.
[Operand format]
Identifier
saddr Label or FE20H to FF1FH immediate data
saddrp Label or FE20H to FF1FH immediate data (even address only)
[Description example]
MOV FE90H, #50H; When setting saddr to FE90H and the immediate data to 50H
Instruction code
[Illustration]
7
OP code
saddr-offset
15
Effective
1 1 1
address
When 8-bit immediate data is 20H to FFH,
When 8-bit immediate data is 00H to 1FH,
CHAPTER 4 CPU ARCHITECTURE
Description
1 1 1 1
1 0 0 1
0 1 0 1
0
8
α
1 1 1 1
α
α
User's Manual U14826EJ5V0UD
0 1 0 1 OP code
0 0 0 0 90H (saddr-offset)
0 0 0 0 50H (immediate data)
0
= 0.
= 1.
Short direct memory
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