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CHAPTER 3 CPU ARCHITECTURE
User’s Manual U15798EJ2V0UD
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 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 the
[Illustration]
below.
[Operand format]
Identifier
Description
saddr
Label or immediate data indicating FE20H to FF1FH
saddrp
Label or immediate data (even address only) indicating FE20H
to FF1FH
[Description example]
MOV 0FE30H, A; when transferring the value of the A register to saddr (FE30H)
Operation code
1 1 1 1 0 0 1 0
OP code
0 0 1 1 0 0 0 0
30H (saddr-offset)
[Illustration]
15
0
Short direct memory
Effective address
1
1
1
1
1
1
1
8 7
0
7
OP code
saddr-offset
α
When 8-bit immediate data is 20H to FFH,
α
= 0
When 8-bit immediate data is 00H to 1FH,
α
= 1
Содержание mPD780344 Series
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