SN8P1602A datasheet(20/76 Pages) SONIX

20 / 76 page

SN8P1602B

8-Bit Micro-Controller

SONiX TECHNOLOGY CO., LTD

Page 20

Version 1.2

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. It is

easy to make a multi-jump program depends on the value of the accumulator (A).

When carry flag occurs after executing of “ADD PCL, A”, it will not affect PCH register. Users have to check if the jump

table crosses over the ROM page boundary or the listing file generated by SONIX assembly software. We suggest

users to place the jump table at the beginning of the program memory page (xx00H) to avoid errors to occur when

editing the program.

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

enter the

wrong

address

0x0000

and

the

system

will

unexpected

operation

mode.

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 (Incorrect): If the “jump table” crosses over ROM boundary, the program will cause the

errors to occur.

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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