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HT86070 Datasheet(PDF) 8 Page - Holtek Semiconductor Inc |
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HT86070 Datasheet(HTML) 8 Page - Holtek Semiconductor Inc |
8 / 25 page HT86030/HT86070 Rev. 1.00 8 February 20, 2006 Functional Description Execution Flow The system clock for the HT86030/HT86070 series is derived from either a crystal or an RC oscillator. It is in- ternally 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 one instruction cycle while de- coding and execution takes the next instruction cycle. However, the pipelining scheme causes each instruc- tion to effectively execute within one cycle. If an instruc- tion changes the program counter, two cycles are required to complete the instruction. Program Counter - PC The 13-bit program counter (PC) controls the sequence in which the instructions stored in program ROM are ex- ecuted. 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. When executing a jump instruction, conditional skip ex- ecution, loading PCL register, subroutine call, initial re- set, internal interrupt, external interrupt or return from subroutine, the PC manipulates the program transfer by loading the address corresponding to each instruction. Mode Program Counter *12 *11 *10 *9 *8 *7 *6 *5 *4 *3 *2 *1 *0 Initial Reset 0000000000000 External or Serial Input Interrupt 0000000000100 Timer/Event Counter 0 Overflow 0000000001000 Timer/Event Counter 1 Overflow 0000000001100 Timer Counter 3 Overflow 0000000010100 Skip Program Counter+2 Loading PCL *12 *11 *10 *9 *8 @7 @6 @5 @4 @3 @2 @1 @0 Jump, Call Branch #12 #11 #10 #9 #8 #7 #6 #5 #4 #3 #2 #1 #0 Program Counter Note: *12~*0: Program counter bits S12~S0: Stack register bits #12~#0: Instruction code bits @7~@0: PCL bits T 1 T 2 T 3 T 4 T 1 T 2 T 3 T 4 T 1 T 2 T 3 T 4 F e t c h I N S T ( P C ) E x e c u t e I N S T ( P C - 1 ) F e t c h I N S T ( P C + 1 ) E x e c u t e I N S T ( P C ) F e t c h I N S T ( P C + 2 ) E x e c u t e I N S T ( P C + 1 ) P C P C + 1 P C + 2 S y s t e m C l o c k O S C ( R C o n l y ) P C P 1 P 2 P 3 P 4 I n t e r n a l P h a s e C l o c k s Execution Flow |
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