Short Direct Addressing - NEC 78K0 User 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. 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 a part of the overall SFR area.
Ports that are frequently accessed in a program and compare and capture registers of the timer/event counter
are mapped in this area, allowing SFRs to 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 cleared to 0. When it is at 00H to
1FH, bit 8 is set to 1. Refer to [Illustration].
[Operand format]
Identifier
saddr
saddrp
[Description example]
MOV 0FE30H, A; when transferring value of A register to saddr (FE30H)
Operation code
[Illustration]
7
15
Effective address 1 1
When 8-bit immediate data is 20H to FFH,
When 8-bit immediate data is 00H to 1FH,
CHAPTER 3 CPU ARCHITECTURE
Immediate data that indicates label or FE20H to FF1FH
Immediate data that indicates label or FE20H to FF1FH (even address only)
1 1 1 1
0 0 1 1
0
OP code
saddr-offset
8 7
α
1 1 1 1 1
α
= 0
α
= 1
User's Manual U16227EJ2V0UD
Description
0 0 1 0 OP code
0 0 0 0 30H (saddr-offset)
0
Short direct memory
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