S3C72G9 Samsung semiconductor, S3C72G9 Datasheet - Page 2

• Manufacturer Part Number: S3C72G9
• Description: The S3C72G9 single-chip CMOS microcontroller has been designed for high performance using Samsungs newest 4-bit CPU core/ SAM47 (Samsung Arrangeable M
• Manufacturer: Samsung semiconductor

 


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.


LD
LD
LD
Instruction
Table 5-1. Valid 1-Byte Instruction Combinations for REF Look-Ups
First 1-Byte Instruction
A, #im
A, @RRa
@HL, A
Operand
INCS
INCS
DECS
INCS
INCS
DECS
INCS
INCS
DECS
Instruction






Second 1-Byte Instruction






R
RRb
R
R
RRb
R
R
RRb
R
Operand