SN8P1602B
8-Bit Micro-Controller
STACK OPERATION EXAMPLE
The two kinds of Stack-Save operations refer to the stack pointer (STKP) and write the content of program counter (PC)
to the stack buffer are CALL instruction and interrupt service. Under each condition, the STKP decreases and points to
the next available stack location. The stack buffer stores the program counter about the op-code address. The
Stack-Save operation is as the following table.
ꢀ
SN8P1602B
Stack Level
STKP Register
Stack Buffer
Description
STKPB2
STKPB1
STKPB0
High Byte Low Byte
1
1
1
1
0
0
1
1
0
0
1
1
1
0
1
0
1
0
Free
STK0H
STK1H
STK2H
STK3H
-
Free
STK0L
STK1L
STK2L
STK3L
-
0
1
2
3
4
-
-
-
-
-
> 4
Stack Over, error
There are Stack-Restore operations correspond to each push operation to restore the program counter (PC). The RETI
instruction uses for interrupt service routine. The RET instruction is for CALL instruction. When a pop operation occurs,
the STKP is incremented and points to the next free stack location. The stack buffer restores the last program counter
(PC) to the program counter registers. The Stack-Restore operation is as the following table.
ꢀ
SN8P1602B
Stack Level
STKP Register
Stack Buffer
Description
STKPB2
STKPB1
STKPB0
High Byte Low Byte
0
1
1
1
1
1
0
0
1
1
1
0
1
0
1
STK3H
STK2H
STK1H
STK0H
Free
STK3L
STK2L
STK1L
STK0L
Free
4
3
2
1
0
-
-
-
-
-
PROGRAM COUNTER
The program counter (PC) is a 10-bit binary counter separated into the high-byte 2 and the low-byte 8 bits. This
counter is responsible for pointing a location in order to fetch an instruction for kernel circuit. Normally, the program
counter is automatically incremented with each instruction during program execution.
Besides, it can be replaced with specific address by executing CALL or JMP instruction. When JMP or CALL instruction
is executed, the destination address will be inserted to bit 0 ~ bit 9.
SN8P1602B
Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
PC
-
-
-
-
-
-
PC9 PC8 PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0
After
reset
-
-
-
-
-
-
0
0
0
0
0
0
0
0
0
0
PCH
PCL
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