HT48CU80 Holtek Semiconductor, HT48CU80 Datasheet - Page 7

• Manufacturer Part Number: HT48CU80
• Description: (HT48RU80 / HT48CU80) I/O Type 8-Bit MCU
• Manufacturer: Holtek Semiconductor

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Functional Description
Execution Flow
The system clock for the microcontroller is derived from
either a crystal or an RC oscillator. The system clock is
internally divided into four non-overlapping clocks. One
instruction cycle consists of four system clock cycles.
Instruction fetching and execution are pipelined in such
a way that a fetch takes an instruction cycle while de-
coding and execution takes the next instruction cycle.
However, the pipelining scheme causes each instruc-
tion to be effectively executed in a cycle. If an instruction
changes the program counter, two cycles are required to
complete the instruction.
Program Counter - PC
The program counter (PC) controls the sequence in
which the instructions stored in the program ROM are
executed and its contents specify a full range of pro-
gram memory.
After accessing a program memory word to fetch an in-
struction code, the contents of the program counter are
incremented by one. The program counter then points to
the memory word containing the next instruction code.
Note: *13~*0: Program counter bits
Rev. 1.00
Initial Reset
External Interrupt 0
Timer/Event Counter 0 Overflow
Timer/Event Counter 1 Overflow
Timer/Event Counter 2 Overflow
External Interrupt 1
UART Interrupt
Skip
Loading PCL
Jump, Call Branch
Return (RET, RETI)
#13~#0: Instruction code bits
Mode
BP.5 #12 #11 #10
S13 S12 S11 S10
*13
*13
0
0
0
0
0
0
0
*12
*12
0
0
0
0
0
0
0
*11
*11
0
0
0
0
0
0
0
Program Counter
Execution Flow
*10
*10
0
0
0
0
0
0
0
7
#9
S9
*9
*9
0
0
0
0
0
0
0
When executing a jump instruction, conditional skip ex-
ecution, loading register, subroutine call or return from
subroutine, initial reset, internal interrupt, external inter-
rupt or return from interrupts, the PC manages the pro-
gram transfer by loading the address corresponding to
each instruction.
The conditional skip is activated by instructions. Once
the condition is met, the next instruction, fetched during
the current instruction execution, is discarded and a
dummy cycle replaces it to get the proper instruction.
Otherwise proceed with the next instruction.
The lower byte of the program counter (PCL) is a read-
able and writeable register (06H). Moving data into the
PCL performs a short jump. The destination will be
within the current program ROM page.
When a control transfer takes place, an additional
dummy cycle is required.
Program Memory - ROM
The program memory is used to store the program in-
structions which are to be executed. It also contains
data, table, and interrupt entries, and is organized into
S13~S0: Stack register bits
@7~@0: PCL bits
#8
S8
Program Counter+2
*8
*8
0
0
0
0
0
0
0
Program Counter
@7 @6 @5 @4 @3 @2 @1 @0
#7
S7
*7
0
0
0
0
0
0
0
#6
S6
*6
0
0
0
0
0
0
0
HT48RU80/HT48CU80
S5
#5
*5
0
0
0
0
0
0
0
S4
#4
*4
0
0
0
0
1
1
1
S3
#3
*3
0
0
1
1
1
0
0
S2
#2
*2
0
1
0
1
0
0
1
April 12, 2006
S1
#1
*1
0
0
0
0
0
0
0
S0
#0
*0
0
0
0
0
0
0
0