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HT46C63 Datasheet(PDF) 8 Page - Holtek Semiconductor Inc |
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HT46C63 Datasheet(HTML) 8 Page - Holtek Semiconductor Inc |
8 / 44 page HT46R63/HT46C63 Rev. 1.90 8 May 17, 2004 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 P C Execution Flow Mode Program Counter *11~*8 *7 *6 *5 *4 *3 *2 *1 *0 Initial Reset 0000 00000000 External Interrupt 0 0000 00000100 External Interrupt 1 0000 00001000 Timer/Event Counter Overflow 0000 00001100 Time Base Time-out 0000 00010000 A/D Interrupt 0000 00010100 RTC Interrupt 0000 00011000 Skip PC+2 Loading PCL @11~@8 @7 @6 @5 @4 @3 @2 @1 @0 Jump, Call Branch #11~#8 #7 #6 #5 #4 #3 #2 #1 #0 Return (RET, RETI) S11~S8 S7 S6 S5 S4 S3 S2 S1 S0 Program Counter Note: *11~*0: Program counter bits S11~S0: Stack register bits #11~#0: Instruction code bits @7~@0: PCL bits Functional Description Execution Flow The system clock for the microcontroller is derived from an external RC or crystal oscillator. The system clock is internally divided into four non-overlapping clocks. One instruction cycle consists of 4 system clock cycles. Instruction fetching and execution are pipelined in such a way that a fetch and decoding takes an instruction cy- cle while execution take the next instruction cycle. How- ever, the pipelining scheme causes each instruction to effectively execute in a cycle. If an instruction changes the program counter, two cycles are required to com- plete the instruction. Program Counter - PC The program counter controls the sequence in which the instructions stored in the program memory are executed and its contents specify full range of program 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. When executing a jump instruction, conditional skip ex- ecution, loading PCL (program counter lower-order byte register), subroutine call, initial reset, interrupts or return from subroutine or interrupts, the program counter ma- nipulates the program 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-order byte of the program counter (PCL) can be accessed by using software instructions. Moving data into the PCL performs a short jump. The destina- tion will be within the current program ROM page. Once the control transfer takes place, the execution suf- fers from having an additional dummy cycle. Program Memory - PROM 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 |
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