HT45F4M View Datasheet(PDF) - Holtek Semiconductor

Part Name

Description

Manufacturer

HT45F4M

Lithium Battery Backup Power ASSP MCU

Holtek Semiconductor 

HT45F4M

Lithium Battery Backup Power ASSP MCU

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 nor part of the program space, and is neither readable nor

writeable. The activated level is indexed by the Stack Pointer, 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.

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 CALL subroutine 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. If the stack is overflow, the first Program

Counter save in the stack will be lost.

P ro g ra m C o u n te r

T o p o f S ta c k

S ta c k

P o in te r

B o tto m o f S ta c k

S ta c k L e v e l 1

S ta c k L e v e l 2

S ta c k L e v e l 3

S ta c k L e v e l 4

P ro g ra m

M e m o ry

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:

• 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. 1.10

16

January 15, 2013

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