Rev. 1.10
118
November 26, 2019
Rev. 1.10
119
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
Logical and Rotate Operation
The standard logical operations such as AND, OR, XOR and CPL all have their own instruction
within the Holtek microcontroller instruction set. As with the case of most instructions involving
data manipulation, data must pass through the Accumulator which may involve additional
programming steps. In all logical data operations, the zero flag may be set if the result of the
operation is zero. Another form of logical data manipulation comes from the rotate instructions such
as RR, RL, RRC and RLC which provide a simple means of rotating one bit right or left. Different
rotate instructions exist depending on program requirements. Rotate instructions are useful for serial
port programming applications where data can be rotated from an internal register into the Carry
bit from where it can be examined and the necessary serial bit set high or low. Another application
which rotate data operations are used is to implement multiplication and division calculations.
Branches and Control Transfer
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.
Bit Operations
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 "SET [m].i" or "CLR [m].
i" 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.
Table Read Operations
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.
Other Operations
In addition to the above functional instructions, a range of other instructions also exist such as
the "HALT" 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.
