Rev. 1.00
14
March 24, 2020
Rev. 1.00
15
March 24, 2020
BS83A04C
4-Key Enhanced Touch I/O Flash MCU
BS83A04C
4-Key Enhanced Touch I/O Flash MCU
one instruction cycle. Although the fetching and execution of instructions takes place in consecutive
instruction cycles, the pipelining structure of the microcontroller ensures that instructions are
effectively executed in one instruction cycle. The exception to this are instructions where the
contents of the Program Counter are changed, such as subroutine calls or jumps, in which case the
instruction will take one more instruction cycle to execute.
For instructions involving branches, such as jump or call instructions, two machine cycles are required to
complete instruction execution. An extra cycle is required as the program takes one cycle to first obtain
the actual jump or call address and then another cycle to actually execute the branch. The requirement
for this extra cycle should be taken into account by programmers in timing sensitive applications.
Fetch Inst. (PC)
(System Clock)
f
SYS
Phase Clock T1
Phase Clock T2
Phase Clock T3
Phase Clock T4
Program Counter
PC
PC+1
PC+2
Pipelining
Execute Inst. (PC-1)
Fetch Inst. (PC+1)
Execute Inst. (PC)
Fetch Inst. (PC+2)
Execute Inst. (PC+1)
System Clocking and Pipelining
Fetch Inst. 1
1 MOV A,[12H]
2 CALL DELAY
3 CPL [12H]
4 :
5 :
6 DELAY: NOP
Execute Inst. 1
Fetch Inst. 2
Execute Inst. 2
Fetch Inst. 3
Flush Pipeline
Fetch Inst. 6
Execute Inst. 6
Fetch Inst. 7
Instruction Fetching
Program Counter
During program execution, the Program Counter is used to keep track of the address of the
next instruction to be executed. It is automatically incremented by one each time an instruction
is executed except for instructions, such as “JMP” or “CALL” that demand a jump to a non-
consecutive Program Memory address. Only the lower 8 bits, known as the Program Counter Low
Register, are directly addressable by the application program.
When executing instructions requiring jumps to non-consecutive addresses such as a jump instruction,
a subroutine call, interrupt or reset, etc., the microcontroller manages program control by loading
the required address into the Program Counter. For conditional skip instructions, once the condition
has been met, the next instruction, which has already been fetched during the present instruction
execution, is discarded and a dummy cycle takes its place while the correct instruction is obtained.
Program Counter
Program Counter High Byte
PCL Register
PC9~PC8
PCL7~PCL0
Program Counter
