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CHAPTER 3
CPU ARCHITECTURE
User’s Manual U12790EJ2V0UD
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.
The fixed space to which this addressing is applied is the 256-byte space FE20H to FF1FH. An internal RAM
and special-function registers (SFRs) are mapped at FE20H to FEFFH and FF00H to FF1FH, respectively.
The SFR area (FF00H to FF1FH) where short direct addressing is applied is part of the total the SFR area. In
this area, ports which are frequently accessed in a program and a compare register 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 [Illustration] below.
[Operand format]
Symbol
Description
saddr
Label or immediate data indicating FE20H to FF1FH
saddrp
Label or immediate data indicating FE20H to FF1FH
(even addresses only)
[Example]
MOV FE30H, A; when transferring the value of register A to saddr (FE30H)
Operation code
11110010
Opcode
00110000
30H (saddr-offset)
[Illustration]
When 8-bit immediate data is 20H to FFH,
α = 0
When 8-bit immediate data is 00H to 1FH,
α = 1
15
0
Short direct memory
Effective address
1
111111
87
0
7
OP code
saddr-offset
α