HT46R064D/065D/066D
Enhanced A/D Type 8-Bit OTP MCU with LED Driver
Stack
This is a special part of the memory which is used to save the contents of the Program Counter only.
The stack is neither part of the Data or Program Memory 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 contents of the Program Counter are pushed onto
the stack. At the end of a subroutine or an interrupt routine, signaled 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.
Device
HT46R064D
Stack Levels
4
6
HT46R065D/HT46R066D
If the stack is full and an enabled interrupt takes place, the interrupt request flag will be recorded but
the acknowledge signal will be inhibited. When the Stack Pointer is decremented, by RET or RETI,
the interrupt will be serviced. This feature prevents stack overflow allowing the programmer to use
the structure more easily. However, when the stack is full, a CALLsubroutine instruction 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.
Arithmetic and Logic Unit - ALU
The arithmetic-logic unit or ALU is a critical area of the microcontroller that carries out arithmetic and
logic operations of the instruction set. Connected to the main microcontroller data bus, the ALU
receives related instruction 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 operations may
result in carry, borrow or other status changes, the status register will be correspondingly updated to
reflect these changes. The ALU supports the following functions:
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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
Rev. 1.00
15
January 12, 2011
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
