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HT82A520R Datasheet(PDF) 9 Page - Holtek Semiconductor Inc |
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HT82A520R Datasheet(HTML) 9 Page - Holtek Semiconductor Inc |
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9 / 72 page  HT82A520R/HT82A620R Rev.1.30 9 January14,2011 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- rectinstructionisobtained. 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 befoundintheSpecialFunctionRegistersection. 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 topofthestack. If the stack is full and an enabled interrupt takes place, the interrupt request flag will be recorded but the ac- knowledge signal will be inhibited. When the Stack Pointer is decremented, by RET or RETI, the interrupt will be serviced. This feature prevents stack overflow al- lowing the programmer to use the structure more easily. However, when the stack is full, a CALL subroutine in- struction can still be executed which will result in a stack overflow. Precautions should be taken to avoid such cases which might cause unpredictable program branching. ArithmeticandLogicUnit - ALU The arithmetic-logic unit or ALU is a critical area of the microcontroller that carries out arithmetic and logic op- erations of the instruction set. Connected to the main microcontroller data bus, the ALU receives related in- struction codes and performs the required arithmetic or logical operations after which the result will be placed in the specified register. As these ALU calculation or oper- ations may result in carry, borrow or other status changes, the status register will be correspondingly up- dated to reflect these changes. The ALU supports the followingfunctions. Mode ProgramCounterBits b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 InitialReset 0 0 0 0 0 0 0 0 0 0 0 0 USB Interrupt 0 0 0 0 0 0 0 0 0 1 0 0 ExternalInterrupt 0 0 0 0 0 0 0 0 1 0 0 0 Timer/EventCounter Overflow 0 0 0 0 0 0 0 0 1 1 0 0 SPIInterrupt 0 0 0 0 0 0 0 1 0 0 0 0 Skip ProgramCounter+2 Loading PCL PC11 PC10 PC9 PC8 @7 @6 @5 @4 @3 @2 @1 @0 Jump,CallBranch #11 #10 #9 #8 #7 #6 #5 #4 #3 #2 #1 #0 ReturnfromSubroutine S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1 S0 ProgramCounter Note: PC11~PC8:CurrentProgramCounterbits @7~@0: PCL bits #11~#0:Instructioncodeaddressbits S11~S0:Stackregisterbits 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 |
Similar Part No. - HT82A520R_11 |
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Similar Description - HT82A520R_11 |
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