Short Direct Addressing - NEC mPD780973 Series Preliminary User's Manual

3.4.4 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 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.
If the SFR area (FF00H to FF1FH) where short direct addressing is applied, ports which are frequently accessed
in a program and a compare register of the timer/event counter and a capture 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. Refer to [Operation] below.
[Operand format]
Identifier
saddr
saddrp
[Description example]
MOV 0FE30H, #50H; when setting saddr to FE30H and immediate data to 50H
[Operation]
7
15
Effective Address
1 1 1
When 8-bit immediate data is 20H to FFH, α = 0
When 8-bit immediate data is 00H to 1FH, α = 1
CHAPTER 3 CPU ARCHITECTURE
Label or FE20H to FF1FH immediate data
Label or FE20H to FF1FH immediate data (even address only)
Operation code
0
OP code
saddr-offset
8 7
α
1 1 1 1
Description
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)
0
Short Direct Memory
61