HT48E10 Holtek Semiconductor, HT48E10 Datasheet - Page 5

• Manufacturer Part Number: HT48E10
• Description: I/O Type 8-Bit MTP MCU
• Manufacturer: Holtek Semiconductor

Functional Description
Execution Flow
The HT48E10 system clock is derived from either a
crystal or an RC oscillator and is internally divided into
four non-overlapping clocks. One instruction cycle con-
sists 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.
This pipelining scheme ensures that instructions are ef-
fectively executed in one cycle. If an instruction changes
the contents of the program counter, such as subroutine
calls or jumps, in which case, 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
Note: *9~*0: Program counter bits
Rev. 1.50
Initial Reset
External Interrupt
Timer/Event Counter Overflow
Skip
Loading PCL
Jump, Call Branch
Return from Subroutine
#9~#0: Instruction code bits
Mode
S9
#9
*9
*9
0
0
0
S8
#8
*8
*8
0
0
0
Program Counter
Execution Flow
@7
S7
#7
*7
0
0
0
5
@6
#6
S6
incremented by one. The program counter then points to
the memory word containing the next instruction code.
When executing a jump instruction, conditional skip ex-
ecution, loading into the PCL register, subroutine call or
return from subroutine, initial reset, internal interrupt,
external interrupt or return from interrupt, the PC man-
ages the program transfer by loading the address corre-
sponding 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 256 locations.
When a control transfer takes place, an additional
dummy cycle is required.
*6
S9~S0: Stack register bits
@7~@0: PCL bits
0
0
0
Program Counter+2
Program Counter
@5
S5
#5
*5
0
0
0
@4
S4
#4
*4
0
0
0
@3
S3
#3
*3
0
0
1
@2
S2
#2
*2
0
1
0
October 31, 2006
www.DataSheet4U.com
@1
HT48E10
#1
S1
*1
0
0
0
@0
S0
#0
*0
0
0
0