SN8P2604A
8-Bit Micro-Controller
2.1.1.4 JUMP TABLE DESCRIPTION
The jump table operation is one of multi-address jumping function. Add low-byte program counter (PCL) and ACC
value to get one new PCL. If PCL is overflow after PCL+ACC, PCH adds one automatically. The new program counter
(PC) points to a series jump instructions as a listing table. It is easy to make a multi-jump program depends on the
value of the accumulator (A).
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Note: PCH only support PC up counting result and doesn’t support PC down counting. When PCL is
carry after PCL+ACC, PCH adds one automatically. If PCL borrow after PCL–ACC, PCH keeps value and
not change.
Example: Jump table.
ORG
0X0100
; The jump table is from the head of the ROM boundary
B0ADD
JMP
JMP
JMP
JMP
PCL, A
; PCL = PCL + ACC, PCH + 1 when PCL overflow occurs.
; ACC = 0, jump to A0POINT
; ACC = 1, jump to A1POINT
; ACC = 2, jump to A2POINT
; ACC = 3, jump to A3POINT
A0POINT
A1POINT
A2POINT
A3POINT
SONIX provides a macro for safe jump table function. This macro will check the ROM boundary and move the jump
table to the right position automatically. The side effect of this macro maybe wastes some ROM size.
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Example: If “jump table” crosses over ROM boundary will cause errors.
@JMP_A
MACRO
IF
VAL
(($+1) !& 0XFF00) !!= (($+(VAL)) !& 0XFF00)
JMP
($ | 0XFF)
($ | 0XFF)
ORG
ENDIF
ADD
PCL, A
ENDM
Note: “VAL” is the number of the jump table listing number.
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