HT45F23 datasheet(22/152 Pages) HOLTEK

22 / 152 page

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.

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

Flash Program Memory

The Program Memory is the location where the user code or program is stored. For this device series

the Program Memory is Flash type, which means it can be programmed and re-programmed a large

number of times, allowing the user the convenience of code modification on the same device. By using

the appropriate programming tools, these Flash devices offer users the flexibility to conveniently

debug and develop their applications while also offering a means of field programming and updating.

Structure

The Program Memory has a capacity of 2K

´15 . The Program Memory is addressed by the Program

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 reserved 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 0. If the external interrupt pin receives an active edge, the

program will jump to this location and begin execution if the external interrupt is enabled and the

stack is not full.

Rev. 1.20

September 15, 2011

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

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