ADDRESS SPACES KS57C2308/P2308/C2316/P2316
2-4
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)
•
•
•