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HT46R46E Datasheet(PDF) 10 Page - Holtek Semiconductor Inc |
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HT46R46E Datasheet(HTML) 10 Page - Holtek Semiconductor Inc |
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10 / 73 page  HT46R46E/C46E/R47E/C47E/R48AE/C48AE/R49E Rev. 1.20 10 August 15, 2007 Stack This is a special part of the memory which is used to save the contents of the Program Counter only. The stack can have either 4 or 6 levels depending upon which device is selected and is neither part of the data nor part of the program space, and is neither readable nor writable. The activated level is indexed by the Stack Pointer, SP, and is neither readable nor writable. 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. 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. Note: For the HT46R46E, 4 levels of stack are avail- able and for the HT46R47E, HT46R48AE and HT46R49E, 6 levels of stack are available. Arithmetic and Logic Unit - 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 following functions: · Arithmetic operations: ADD, ADDM, ADC, ADCM, SUB, SUBM, SBC, SBCM, DAA · Logic operations: AND, OR, XOR, ANDM, ORM, XORM, CPL, CPLA · Rotation RRA, RR, RRCA, RRC, RLA, RL, RLCA, RLC · Increment and Decrement INCA, INC, DECA, DEC · Branch decision, JMP, SZ, SZA, SNZ, SIZ, SDZ, SIZA, SDZA, CALL, RET, RETI Program Memory The Program Memory is the location where the user code or program is stored. For microcontrollers, two types of Program Memory are usually supplied. The first type is the One-Time Programmable, OTP, memory where us- ers can program their application code into the device. Devices with OTP memory are denoted by having an ²R² within their device name. By using the appropriate pro- gramming tools, OTP devices offer users the flexibility to freely develop their applications which may be useful dur- ing debug or for products requiring frequent upgrades or program changes. OTP devices are also applicable for use in applications that require low or medium volume production runs. The other type of memory is the mask ROM memory, denoted by having a ²C² within the device name. These devices offer the most cost effective solu- tions for high volume products. Structure The Program Memory has a capacity of 1K by 14, 2K by 14 or 4K by 15 bits depending upon which device is se- lected. The Program Memory is addressed by the Pro- gram Counter and also contains data, table information and interrupt entries. Table data, which can be setup in any location within the Program Memory, is addressed by separate table pointer registers. Special Vectors Within the Program Memory, certain locations are re- served for special usage such as reset and interrupts. · Location 000H This vector is reserved for use by the device reset for program initialisation. After a device reset is initiated, the program will jump to this location and begin execution. · Location 004H This vector is used by the external interrupt. If the ex- ternal interrupt pin on the device goes low, the pro- gram will jump to this location and begin execution if the external interrupt is enabled and the stack is not full. · Location 008H This internal vector is used by the Timer/Event Coun- ter. If a counter overflow occurs, the program will jump to this location and begin execution if the timer/event counter interrupt is enabled and the stack is not full. 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 N 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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