SN8P2977
8-Bit Micro-Controller with Regulator, PGIA, 24-bit ADC
SONiX TECHNOLOGY CO., LTD
Page 23
V1.7
2.1.2.2
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 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.
Note: Program count
er can’t carry from PCL to PCH when PCL is overflow after executing addition
instruction.
Example: Jump table.
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
…
…
