Finding a reference to DASM while researching yesterday’s post @jpluimers on Twitter: “@b0rk @jilles_com Acids vs bases.”, it felt even more like a trip like memory lane as I had used it in the 1980s on Apple ][ and Apple //e after mainly using EDASM. Lisa and Merlin.
I am glad that it is still alive and kicking with home page at [Wayback/Archive] dasm – macro assembler for 8-bit machines and repository at [Wayback/Archive] dasm-assembler/dasm: Macro assembler with support for several 8-bit microprocessors.
Especially this history section on the home page rang a bell:
- Matthew Dillon started dasm in 1987-1988.
- Olaf “Rhialto” Seibert extended dasm in 1995.
- Andrew “Dr.Boo” Davie maintained dasm in 2003-2008.
- Peter Fröhlich maintained dasm in 2008-2015.
- In 2019, the dasm source code and releases were moved to GitHub.
More links from this trip down memory lane:
Last year, #Appril][ got rebranded into #AprilApples, so I wish you a happy retro-month filled with April Apples!
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There is a Blast-RADIUS exploit that makes many uses of 
The Wiert Corner - irregular stream of stuff 
Depends upon which machine and ROM version you have.
The original Apple II monitor does have an S command to single step code in the Monitor. That was removed however to add other features and was not restored until ROM00 of the //c. There are however various 3rd-party ROM images that also have the Step and Trace commands, for example ROMeX and ROM4X, APPLEII.EDM, etc.
There are also hardware boards available to do this as well