A machine code monitor ( machine language monitor) is

software Software is a set of computer programs and associated software documentation, documentation and data (computing), data. This is in contrast to Computer hardware, hardware, from which the system is built and which actually performs the work. ...

that allows a user to enter commands to view and change memory locations on a computer, with options to load and save memory contents from/to secondary storage. Some full-featured machine code monitors provide detailed control ("single-stepping") of the execution of machine language programs (much like a debugger), and include absolute-address code assembly and disassembly capabilities. Motorola published the

MIKBUG MIKBUG is a ROM monitor from Motorola for the Motorola 6800 8-bit microprocessor. It is intended to "be used to debug and evaluate a user's program". MIKBUG was distributed by Motorola in 1974 on a 1 K ROM chip part number MCM6830L7. It ...

ROM monitor for the 6800 in 1973 and the BUFFALO ROM monitor for the 68HC11. Machine code monitors became popular during the home computer era of the 1970s and 1980s and were sometimes available as resident

firmware In computing, firmware is a specific class of computer software that provides the low-level control for a device's specific hardware. Firmware, such as the BIOS of a personal computer, may contain basic functions of a device, and may provide ...

in some computers (e.g., the built-in monitors in the Commodore 128, Heathkit H89 and Zenith laptops). Often, computer manufacturers rely on their ROM-resident monitors to permit users to reconfigure their computers following installation of upgrade hardware, such as expanded main memory, additional disk drives, or different video displays. It was not unheard of to perform all of one's programming in a monitor in lieu of a full-fledged symbolic assembler. Even after full-featured assemblers became readily available, a machine code monitor was indispensable for

debugging In computer programming and software development, debugging is the process of finding and resolving ''bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve in ...

programs. The usual technique was to set break points in the code undergoing testing (e.g., with a BRK instruction in 6502 assembly language) and start the program. When the

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

encountered a break point, the test program would be interrupted and control would be transferred to the machine code monitor. Typically, this would trigger a register dump and then the monitor would await programmer input. Activities at this point might include examining memory contents, patching code and/or perhaps altering the processor registers prior to restarting the test program. The general decline of scratch-written assembly language

has made the use of a machine code monitor somewhat of a lost art. In most systems where higher-level languages are employed, debuggers are used to present a more abstract and friendly view of what is happening within a program. However, the use of machine code monitors persists, especially in the area of hobby-built computers.{{cn, date=February 2017

References

* Microcomputer software