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HT82A6208 Datasheet(PDF) 9 Page - Holtek Semiconductor Inc |
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HT82A6208 Datasheet(HTML) 9 Page - Holtek Semiconductor Inc |
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9 / 98 page  HT82A623R/HT82A6208/HT82A6216 Rev. 1.10 9 October 30, 2009 Program Counter During program execution, the Program Counter is used to keep track of the address of the next instruction to be executed. It is automatically incremented by one each time an instruction is executed except for instructions, such as ²JMP² or ²CALL² that demand a jump to a non-consecutive Program Memory address. It must be noted that only the lower 8 bits, known as the Program Counter Low Register, are directly addressable by user. When executing instructions requiring jumps to non-consecutive addresses such as a jump instruction, a subroutine call, interrupt or reset, etc., the microcontroller manages program control by loading the required address into the Program Counter. For condi- tional skip instructions, once the condition has been met, the next instruction, which has already been fetched during the present instruction execution, is dis- carded and a dummy cycle takes its place while the cor- rect instruction is obtained. The lower byte of the Program Counter, known as the Program Counter Low register or PCL, is available for program control and is a readable and writeable register. By transferring data directly into this register, a short pro- gram jump can be executed directly, however, as only this low byte is available for manipulation, the jumps are limited to the present page of memory, that is 256 loca- tions. When such program jumps are executed it should also be noted that a dummy cycle will be inserted. The lower byte of the Program Counter is fully accessi- ble under program control. Manipulating the PCL might cause program branching, so an extra cycle is needed to pre-fetch. Further information on the PCL register can be found in the Special Function Register section. Stack This is a special part of the memory which is used to save the contents of the Program Counter only. The stack has 6 levels and is neither part of the data nor part of the program space, and is neither readable nor writeable. The activated level is indexed by the Stack Pointer, SP, and is neither readable nor writeable. At a subroutine call or interrupt acknowledge signal, the con- tents of the Program Counter are pushed onto the stack. At the end of a subroutine or an interrupt routine, sig- naled by a return instruction, RET or RETI, the Program Counter is restored to its previous value from the stack. After a device reset, the Stack Pointer will point to the top of the stack. Mode Program Counter Bits b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 Initial Reset 000000000000 USB Interrupt 000000000100 External Interrupt 000000001000 Timer/Event Counter 0 Overflow 000000001100 SPIA Interrupt 000000010000 SPIB Interrupt 000000010100 Timer/Event Counter 1 Overflow 000000011000 Skip Program Counter + 2 Loading PCL PC11 PC10 PC9 PC8 @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 Program Counter Note: PC11~PC8: Current Program Counter bits @7~@0: PCL bits #11~#0: Instruction code address bits S11~S0: Stack register bits P r o g r a m C o u n t e r S t a c k L e v e l 1 S t a c k L e v e l 2 S t a c k L e v e l 3 S t a c k L e v e l 6 P r o g r a m M e m o r y T o p o f S t a c k S t a c k P o i n t e r B o t t o m o f S t a c k |
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