CHAPTER 3 CPU ARCHITECTURE
User’s Manual U18172EJ2V0UD
45
3.4.2 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 160-byte space FE80H to FF1FH (FE80H to FEFFH
(internal high-speed RAM) + FF00H to FF1FH (special function registers)).
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 80H 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.
Identifier Description
saddr
Label or FE80H to FF1FH immediate data
saddrp
Label or FE80H to FF1FH immediate data (even address only)
[Description example]
EQU DATA1 0FE90H ; DATA1 shows FE90H of a saddr area,
MOV DATA1, #50H
; When setting the immediate data to 50H
Instruction
code 1 1
1
1
0
1
0
1
OP
code
1 0
0
1
0
0
0
0
90H
(saddr-offset)
0 1
0
1
0
0
0
0
50H
(immediate
data)
[Illustration]
15
0
Short direct memory
Effective
address
1
1
1
1
1
1
1
8
0
7
OP code
saddr-offset
α
When 8-bit immediate data is 20H to FFH, = 0.
When 8-bit immediate data is 00H to 1FH, = 1.
α
α