NEC 78K0 Series User Manual page 83

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 high-speed 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 set to 0. When it is at 00H to 1FH,
bit 8 is set to 1. See the [Illustration] shown below.
[Operand format]
Identifier
saddr
saddrp
[Description example]
LB1 EQU 0FE30H ; Defines FE30H by LB1.
:
MOV LB1, A ; When LB1 indicates FE30H of the saddr area and the value of register A is transferred to
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 indicate label or FE20H to FF1FH
Immediate data that indicate label or FE20H to FF1FH (even address only)
that address
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
Preliminary User's Manual U17260EJ3V1UD
Description
0 0 1 0 OP code
0 0 0 0 30H (saddr-offset)
0
Short direct memory
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