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HT95C200 Datasheet(PDF) 6 Page - Holtek Semiconductor Inc |
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HT95C200 Datasheet(HTML) 6 Page - Holtek Semiconductor Inc |
6 / 42 page HT95L100/10P Rev. 0.10 6 October 1, 2002 Preliminary Functional Description Execution flow The system clock for the telephone controller is derived from a 32768Hz crystal oscillator. A built-in frequency up conversion circuit provides dual system clock, namely; 32768Hz and 3.58MHz. The system clock is internally divided into four non-overlapping clocks. One instruc- tion cycle consists of four system clock cycles. Instruc- tion fetching and execution are pipelined in such a way that a fetch takes an instruction cycle while decoding and execution takes the next instruction cycle. The pipelining scheme causes each instruction to be effec- tively executed in a instruction cycle. If an instruction changes the program counter, two instruction 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 instruction code, the contents of the program counter are incremented by 1. The program counter then points to the memory word containing the next in- struction 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 program counter manipulates the pro- gram transfer by loading the address corresponding to each instruction. The conditional skip is activated by in- structions. Once the condition is met, the next instruc- tion, fetched during the current instruction execution, is discarded and a dummy cycle replaces it to get the proper instruction. Otherwise proceed to the next in- struction. The program counter lower order byte register (PCL:06H) is a readable and write-able register. Moving data into the PCL performs a short jump. The destina- tion will be within 256 locations. When a control transfer takes place, an additional dummy cycle is required. T 1 T 2 T 3 T 4 T 1 T 2 T 3 T 4 T 1 T 2 T 3 T 4 . e t c h I N S T ( P C ) E x e c u t e I N S T ( P C - 1 ) . e t c h I N S T ( P C + 1 ) E x e c u t e I N S T ( P C ) . 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 *10 *9 *8 *7 *6 *5 *4 *3 *2 *1 *0 Initial reset 000000000000 External interrupt 000000000100 Timer/Event Counter 0 overflow 000000001000 Timer/Event Counter 1 overflow 000000001100 RTC interrupt 000000010100 Dialer I/O interrupt 000000011000 Skip Program Counter+2 Loading PCL *11 *10 *9 *8 @7 @6 @5 @4 @3 @2 @1 @0 Jump, call branch #11 #10 #9 #8 #7 #6 #5 #4 #3 #2 #1 #0 Return from subroutine S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1 S0 Note: *11~*0: Program counter bits S11~S0: Stack register bits #11~#0: Instruction code bits @7~@0: PCL bits |
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