SN8P1602AX datasheet(22/94 Pages) SONIX

22 / 94 page

SN8P1600

8-bit micro-controller

SONiX TECHNOLOGY CO., LTD

Page 22

Revision 1.94

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.

Example :

ORG

0X0100

; The jump table is from the head of the ROM boundary

B0ADD

PCL, A

; PCL = PCL + ACC, the PCH can’t be changed.

JMP

A0POINT

; ACC = 0, jump to A0POINT

JMP

A1POINT

; ACC = 1, jump to A1POINT

JMP

A2POINT

; ACC = 2, jump to A2POINT

JMP

A3POINT

; ACC = 3, jump to 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).

Example: If “jump table” crosses over ROM boundary will cause errors.

ROM Address

0X00FD

B0ADD

PCL, A

; PCL = PCL + ACC, the PCH can’t be changed.

0X00FE

JMP

A0POINT

; ACC = 0

0X00FF

JMP

A1POINT

; ACC = 1

0X0100

JMP

A2POINT

; ACC = 2

jump table cross boundary here

0X0101

JMP

A3POINT

; ACC = 3

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

VAL

(($+1) !& 0XFF00) !!= (($+(VAL)) !& 0XFF00)

JMP

($ | 0XFF)

ORG

($ | 0XFF)

ENDIF

ADD

PCL, A

ENDM

Note: “VAL” is the number of the jump table listing number.

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