SN8P1600
8-bit micro-controller
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. The new program counter (PC) points to a series jump instructions as a listing table. The
way is easy to make a multi-stage program.
When carry flag occurs after executing of “ADD PCL, A”, it will not affect PCH register. Users have to check if the jump
table leaps over the ROM page boundary or the listing file generated by SONIX assembly software. If the jump table
leaps over the ROM page boundary (e.g. from xxFFH to xx00H), move the jump table to the top of next program
memory page (xx00H). Here one page mean 256 words.
ꢃ
Example :
ORG
0X0100
; The jump table is from the head of the ROM boundary
B0ADD
JMP
JMP
JMP
JMP
PCL, A
; PCL = PCL + ACC, the PCH can’t be changed.
; ACC = 0, jump to A0POINT
; ACC = 1, jump to A1POINT
; ACC = 2, jump to A2POINT
; ACC = 3, jump to A3POINT
A0POINT
A1POINT
A2POINT
A3POINT
In following example, the jump table starts at 0x00FD. When execute B0ADD PCL, A. If ACC = 0 or 1, the jump
table points to the right address. If the ACC is larger then 1 will cause error because PCH doesn't increase one
automatically. We can see the PCL = 0 when ACC = 2 but the PCH still keep in 0. The program counter (PC) will
point to a wrong address 0x0000 and crash system operation. It is important to check whether the jump table
crosses over the boundary (xxFFH to xx00H). A good coding style is to put the jump table at the start of ROM
boundary (e.g. 0100H).
ꢃ Example: If “jump table” crosses over ROM boundary will cause errors.
ROM Address
.
.
.
.
.
.
B0ADD
JMP
JMP
JMP
JMP
.
PCL, A
; PCL = PCL + ACC, the PCH can’t be changed.
; ACC = 0
; ACC = 1
; ACC = 2 ꢀjump table cross boundary here
; ACC = 3
0X00FD
0X00FE
0X00FF
0X0100
0X0101
.
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.
@JMP_A
MACRO
IF
VAL
(($+1) !& 0XFF00) !!= (($+(VAL)) !& 0XFF00)
JMP
($ | 0XFF)
($ | 0XFF)
ORG
ENDIF
ADD
PCL, A
ENDM
ꢂ
Note: “VAL” is the number of the jump table listing number.
SONiX TECHNOLOGY CO., LTD
Page 22
Revision 1.94
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