HT68F13 datasheet(124/161 Pages) HOLTEK

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BranchesandControlTransfer

Program branching takes the form of either jumps to specified locations using the JMP instruction or to

a subroutine using the CALL instruction. They differ in the sense that in the case of a subroutine call,

the program must return to the instruction immediately when the subroutine has been carried out. This

is done by placing a return instruction RET in the subroutine which will cause the program to jump

back to the address right after the CALL instruction. In the case of a JMP instruction, the program

simply jumps to the desired location. There is no requirement to jump back to the original jumping off

point as in the case of the CALL instruction. One special and extremely useful set of branch

instructions are the conditional branches. Here a decision is first made regarding the condition of a

certain data memory or individual bits. Depending upon the conditions, the program will continue with

the next instruction or skip over it and jump to the following instruction. These instructions are the key

to decision making and branching within the program perhaps determined by the condition of certain

input switches or by the condition of internal data bits.

BitOperations

The ability to provide single bit operations on Data Memory is an extremely flexible feature of all

Holtek microcontrollers. This feature is especially useful for output port bit programming where

individual bits or port pins can be directly set high or low using either the

²SET [m].i² or ²CLR [m].i²

instructions respectively. The feature removes the need for programmers to first read the 8-bit output

port, manipulate the input data to ensure that other bits are not changed and then output the port with

the correct new data. This read-modify-write process is taken care of automatically when these bit

operation instructions are used.

TableReadOperations

Data storage is normally implemented by using registers. However, when working with large amounts

of fixed data, the volume involved often makes it inconvenient to store the fixed data in the Data

Memory. To overcome this problem, Holtek microcontrollers allow an area of Program Memory to be

setup as a table where data can be directly stored. A set of easy to use instructions provides the means

by which this fixed data can be referenced and retrieved from the Program Memory.

OtherOperations

In addition to the above functional instructions, a range of other instructions also exist such as the

²HALT² instruction for Power-down operations and instructions to control the operation of the

Watchdog Timer for reliable program operations under extreme electric or electromagnetic

environments. For their relevant operations, refer to the functional related sections.

HT68F13/HT68F14/HT68F15

EnhancedI/OFlashTypeMCU

Rev.1.10

124

February9,2011

HT68F13 Datasheet(PDF) 124 Page - Holtek Semiconductor Inc