Samsung KS57C2308 manual Instruction Reference Area, Incs

SAM47 INSTRUCTION SET KS57C2308/P2308/C2316/P2316

Instruction Reference Area

Using the 1-byte REF (Reference) instruction, you can reference instructions stored in the addresses 0020H–007FH of program memory (the REF instruction look-up table). The location referenced by REF may contain either two 1-byte instructions or a single 2-byte instruction. The starting address of the instruction being referenced must always be an even number.

3-byte instructions such as JP or CALL may also be referenced using REF. To reference these 3-byte instructions, the 2-byte pseudo commands, TJP and TCALL, must be written in the reference.

The PC is not incremented when an REF instruction is executed. After it executes, the program's instruction execution sequence resumes at the address immediately following the REF instruction. By using REF instructions to execute instructions larger than one byte, as well as branches and subroutines, you can reduce the program size. To summarize, the REF instruction can be used in three ways:

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

—Branching to any location by referencing a branch address that is stored in the look-up table;

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

If necessary, an REF instruction can be circumvented by means of a skip operation prior to the REF in the execution sequence. In addition, the instruction immediately following an REF can also be skipped by using an appropriate reference instruction or instructions.

Two-byte instructions can be referenced by using an REF instruction. (An exception is XCH A,DA (note) )

If the MSB value of the first 1-byte instruction in the reference area is “0”, the instruction cannot be referenced by a REF instruction. Therefore, if you use REF to reference two 1-byte instructions stored in the reference area, specific combinations must be used for the first and second 1-byte instruction. These combinations are described in Table5-1.

Table 5-1. Valid 1-Byte Instruction Combinations for REF Look-Ups

First 1-Byte Instruction		Second 1-Byte Instruction
Instruction	Operand	Instruction	Operand
LD	A,#im	INCS (note)	R
		INCS	RRb
		DECS (note)	R
LD	A,@Rra	INCS (note)	R
		INCS	RRb
		DECS (note)	R
LD	@HL,A	INCS (note)	R
		INCS	RRb
		DECS (note)	R

NOTE: The MSB value of the instruction is “0”.

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