SN8F2250B Series
USB 2.0 Full-Speed 8-Bit Micro-Controller
2.3.3 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.
STKP Register
Stack Buffer
High Byte Low Byte
Stack Level
Description
STKPB2
STKPB1
STKPB0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
1
0
1
0
1
0
1
0
1
0
Free
STK0H
STK1H
STK2H
STK3H
STK4H
STK5H
STK6H
STK7H
-
Free
STK0L
STK1L
STK2L
STK3L
STK4L
STK5L
STK6L
STK7L
-
0
1
2
3
4
5
6
7
8
-
-
-
-
-
-
-
-
-
> 8
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.
STKP Register
Stack Buffer
High Byte Low Byte
Stack Level
Description
STKPB2
STKPB1
STKPB0
1
0
0
0
0
1
1
1
1
1
0
0
1
1
0
0
1
1
1
0
1
0
1
0
1
0
1
STK7H
STK6H
STK5H
STK4H
STK3H
STK2H
STK1H
STK0H
Free
STK7L
STK6L
STK5L
STK4L
STK3L
STK2L
STK1L
STK0L
Free
8
7
6
5
4
3
2
1
0
-
-
-
-
-
-
-
-
-
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