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S3C72G9 Datasheet(PDF) 2 Page - Samsung semiconductor |
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S3C72G9 Datasheet(HTML) 2 Page - Samsung semiconductor |
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2 / 96 page  INSTRUCTION REFERENCE AREA Using the 1-byte REF (Reference) instruction, you can reference instructions stored in 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 instead of JP and CALL. The PC is not incremented when a 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 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, a 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 a REF can also be skipped by using an appropriate reference instruction or instructions. Two-byte instruction can be referenced by using a REF instruction (An exception is XCH A, DA). If the MSB value of the first one-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 instruction stored in the reference area, specific combinations must be used for the first and second 1-byte instruction. These combination examples are described in Table 5-1. 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 R INCS RRb DECS R LD A, @RRa INCS R INCS RRb DECS R LD @HL, A INCS R INCS RRb DECS R ,* -./ |
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