Samsung KS57C2308 manual Instruction Reference Area, + Programming TIP Using the REF Look-Up Table

ADDRESS SPACES KS57C2308/P2308/C2316/P2316

INSTRUCTION REFERENCE AREA

Using 1-byte REF instructions, you can easily reference instructions with larger byte sizes that are stored in addresses 0020H–007FH of program memory. This 96-byte area is called the REF instruction reference area, or look-up table. Locations in the REF look-up table may contain two 1-byte instructions, one 2-byte instruction, or one 3-byte instruction such as a JP (jump) or CALL. The starting address of the instruction you are referencing must always be an even number. To reference a JP or CALL instruction, it must be written to the reference area in a two-byte format: for JP, this format is TJP; for CALL, it is TCALL.

By using REF instructions you can execute instructions larger than one byte, In summary, there are three ways you can use the REF instruction:

—Using the 1-byte REF instruction to execute one 2-byte or two 1-byte instructions,

—Branching to any location by referencing a branch instruction stored in the look-up table,

—Calling subroutines at any location by referencing a call instruction stored in the look-up table.

+PROGRAMMING TIP — Using the REF Look-Up Table

Here is one example of how to use the REF instruction look-up table:

	ORG	0020H
JMAIN	TJP	MAIN	;	0, MAIN
KEYCK	BTSF	KEYFG	;	1, KEYFG CHECK
WATCH	TCALL	CLOCK	;	2, CALL CLOCK
INCHL	LD	@HL,A	;	3, (HL) ← A
INCS	HL
	•
	•
	•
ABC	LD	EA,#00H	;	47, EA ← #00H
	ORG	0080H
MAIN	NOP
	NOP
	•
	•
	•
	REF	KEYCK	;	BTSF KEYFG (1-byte instruction)
	REF	JMAIN	;	KEYFG = 1, jump to MAIN (1-byte instruction)
	REF	WATCH	;	KEYFG = 0, CALL CLOCK (1-byte instruction)
	REF	INCHL	;	LD @HL,A
			;	INCS HL
	REF	ABC	;	LD EA,#00H (1-byte instruction)
	•
	•
	•

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