Samsung S3C9228/P9228, 8-Bit CMOS Microcontroller user manual Common Working Register Area C0H-CFH

ADDRESS SPACES S3C9228/P9228

COMMON WORKING REGISTER AREA (C0H–CFH)

The SAM88RCRI register architecture provides an efficient method of working register addressing that takes full advantage of shorter instruction formats to reduce execution time.

This16-byte address range is called common area. That is, locations in this area can be used as working registers by operations that address any location on any page in the register file. Typically, these working registers serve as temporary buffers for data operations between different pages.

The Register (R) addressing mode can be used to access this area

Registers are addressed either as a single 8-bit register or as a paired 16-bit register. In 16-bit register pairs, the address of the first 8-bit register is always an even number and the address of the next register is an odd number. The most significant byte of the 16-bit data is always stored in the even-numbered register; the least significant byte is always stored in the next (+ 1) odd-numbered register.

MSB	LSB
Rn	Rn + 1

n = Even address

Figure 2-3. 16-Bit Register Pairs

+PROGRAMMING TIP — Addressing the Common Working Register Area

As the following examples show, you should access working registers in the common area, locations C0H–CFH, using working register addressing mode only.

Examples:	1.	LD	0C2H,40H	;	Invalid addressing mode!
		Use working register addressing instead:
		LD	R2,40H	;	R2 (C2H) ← the value in location 40H
	2.	ADD	0C3H,#45H	;	Invalid addressing mode!
		Use working register addressing instead:
		ADD	R3,#45H	;	R3 (C3H) ← R3 + 45H

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