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
²
SET [m].i
²
or
²
CLR [m].i
²
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
²
HALT
²
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.
BS83B08-3/B12-3/B16-3/B16G-3/C24-3
8-Bit Touch Key Flash MCU
Rev. 1.50
113
April 28, 2020
