The Zapple Monitor was a
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 h ...
-based product developed by Roger Amidon
at
Technical Design Laboratories (also known as ''TDL''). TDL was based in Princeton, New Jersey, USA in the 1970s and early 1980s.
Advertisement: XITAN Alpha 1 and Alpha 2 from Technical Design Labs
Published 1977, From Volume 1 Issue 1 of ROM Magazine.
The ''Zapple'' monitor was a primitive operating system which could be expanded and used as a Basic Input/Output Services (BIOS
In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...
) 8080 and Z80 based computers. Much of the functionality of Zapple would find its way into applications like 'Debug' in MS-DOS.
Zapple commands would allow a user to examine and modify memory, I/O, execute software (Goto or Call) and had a variety of other commands. The program required little in the way of then expensive Read Only Memory or RAM. An experienced user could use Zapple to test and debug code, verify hardware function, test memory, and so on.
A typical command line would start with a letter such as 'X' (examine memory) followed by a hexadecimal word (the memory address 01AB) and nteror pace
Pace or paces may refer to:
Business
*Pace (transit), a bus operator in the suburbs of Chicago, US
* Pace Airlines, an American charter airline
*Pace Foods, a maker of a popular brand of salsa sold in North America, owned by Campbell Soup Compan ...
After this sequence the content of the memory location would be shown Fand the user could enter a hexadecimal byte 0to replace the contents of the address, or hit pace
Pace or paces may refer to:
Business
*Pace (transit), a bus operator in the suburbs of Chicago, US
* Pace Airlines, an American charter airline
*Pace Foods, a maker of a popular brand of salsa sold in North America, owned by Campbell Soup Compan ...
or nterto move to the next address 1AB An experienced user could enter a small program in this manner, entering machine language from memory.
Because of the simple structure of the program, consisting of a vector table (one for each letter) and a small number of subroutines, and because the source code was readily available, adding or modifying Zapple was straightforward. The dominant operating system of the era, CP/M, required the computer manufacturer or hobbyist to develop hardware specific BIOS. Many users tested their BIOS subroutines using Zapple to verify, for example, a floppy disk track seek command, or read sector command, etc., was functioning correctly by extending Zapple to accommodate these operations in the hardware environment.
The general structure of Zapple lives on in the code of many older programmers working on embedded systems as it provides a simple mechanism to test the hardware before moving to more advanced user interfaces.
References
External links
*
TDL Apple and Zapple monitor
History of software
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