Filter
Top Products
124
CHAPTER 5 CPU ARCHITECTURE
5.4.4 Short direct addressing
[Function]
The memory to be manipulated in the fixed space is directly addressed with 8-bit data in an instruction word.
The fixed space to which this address is applied is a 256-byte space of addresses FE20H through 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 through FF1FH) to which short direct addressing is applied is a part of the entire SFR
area. To this area, ports frequently accessed by the program, and the compare registers and capture registers
of timer/event counters are mapped. These SFRs can be manipulated with a short byte length and a few 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 [Illustration] on next page.
[Operand format]
Identifier Description
saddr Label of FE20H to FF1FH immediate data
saddrp Label of FE20H to FF1FH immediate data (even address only)
15
0
Short Direct Memory
Effective Address
1
111111
87
07
OP code
saddr-offset
α
[Description example]
MOV 0FE30H, #50H; when setting saddr to FE30H and immediate data to 50H
Operation code 0 0 0 10001 OP code
00110000 30H (saddr-offset)
01010000 50H (immediate data)
[Illustration]
When 8-bit immediate data is 20H to FFH, α = 0
When 8-bit immediate data is 00H to 1FH, α = 1