ht82a523r Holtek Semiconductor Inc., ht82a523r Datasheet - Page 6

• Manufacturer Part Number: ht82a523r
• Description: Ht82a523r -- Usb 2.0 Full Speed 8-bit Otp Mcu
• Manufacturer: Holtek Semiconductor Inc.

Functional Description
Execution Flow
The system clock is derived from either a crystal or an
RC oscillator. It is internally divided into four
non-overlapping clocks. One instruction cycle consists
of four system clock cycles. Instruction fetching and ex-
ecution are pipelined in such a way that a fetch takes
one instruction cycle while decoding and execution
takes the next instruction cycle. The pipelining scheme
makes it possible for each instruction to be effectively
executed in a cycle. If an instruction changes the value
of the program counter, two cycles are required to com-
plete 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 program memory.
After accessing a program memory word to fetch an in-
struction code, the contents of the program counter are
Note:
Rev. 1.30
Initial Reset
External Interrupt
Timer/Event Counter 0 Overflow
Timer/Event Counter 1 Overflow
USB Interrupt
Serial Interface Interrupt
Serial Interface 2 Interrupt
Skip
Loading PCL
Jump, Call Branch
Return from Subroutine
*11~*0: Program counter bits
#11~#0: Instruction code bits
Mode
S11
#11
*11
*11
0
0
0
0
0
0
0
S10
#10
*10
*10
0
0
0
0
0
0
0
Program Counter
Execution Flow
S9
#9
*9
*9
0
0
0
0
0
0
0
#8
S8
6
*8
*8
0
0
0
0
0
0
0
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 PCL register, subroutine call or return
from subroutine, initial reset, internal interrupt, external
interrupt or return from interrupts, the PC manipulates
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 to the next instruction.
The lower byte of the program counter (PCL) is a read-
able and write able 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.
S11~S0: Stack register bits
@7~@0: PCL bits
@7
S7
#7
*7
0
0
0
0
0
0
0
Program Counter+2
Program Counter
@6
S6
#6
*6
0
0
0
0
0
0
0
@5
S5
#5
*5
0
0
0
0
0
0
0
@4
S4
#4
*4
0
0
0
0
1
1
1
@3
#3
S3
*3
0
0
1
1
0
0
1
@2
HT82A523R
S2
#2
*2
0
1
0
1
0
1
0
May 13, 2008
@1
S1
#1
*1
0
0
0
0
0
0
0
@0
S0
#0
*0
0
0
0
0
0
0
0