A Javascript 6502 assembly text editor inspired by the Merlin 8 Assembler for the Apple II
This is an incomplete proof of concept demonstrating the use of Javascript and the browser's contenteditable attribute to implement a simple in-browser assembly editor.
- Developing Apple II (6502) assembly code would be easier with a column-oriented editor
- There does not seem to be a good browser-based, cross-platform, open source column-oriented editor appropriate for writing Apple II (6502) assembly.
- Editors like Ace and Monaco don't seem to support column-oriented modes.
- Assembly
- In assembly code, spaces should indicate 'tabstop' breaks
- Online conversations about tabstops, elastic tabstops, etc confirm the need and also show the lack of available solutions that are appropriate for assembly:
- TAB/SHIFT-TAB to move between columns
- also SPACE to moce to the next column
- RETURN/SHIFT-RETURN to add/delete lines
- Merlin source code text can be pasted into the Assembler 8 editor
- The code is formatted in Merlin-style columns
- The code can be edited using standard mouse and keboard input
- The edited code can be exported to Merlin-fiendly, space-delimited text
- Currenty, a proof of concept of a simple in-browser assembly text editor
- Usable, but plenty of issues
- add line numbers option
- convert to Typescript
- add better vertical keyboard navigation
- ...
- integrate a Javascript assembler
- How to build your own WYSIWYG Editor
- contentEditable
- https://ckeditor.com/blog/ContentEditable-The-Good-the-Bad-and-the-Ugly/
- https://javascript.info/mutation-observer
- https://medium.engineering/why-contenteditable-is-terrible-122d8a40e480
- https://medium.com/@adrianmcli/a-beginner-s-guide-to-draft-js-d1823f58d8cc
- https://www.mozzafiller.com/posts/how-does-monaco-editor-enable-text-editing-on-a-web-page
- https://codemirror.net/doc/internals.html
- https://codemirror.net/6/
- Keyboard events
- GetHTML: displays the editor html in the I/O text area
- SetHTML: replaces the editor html with the contents of the I/O text area
- GetText: exports the editor HTML to the I/O text area as Merlin-friendly, space-delimited text
- SetCSS: replaces the active CSS with the contents of the CSS text area
- Reset: restores the editor with example code
- Clear: clears the editor
- ring the BELL
******************************
* RING THE BELL *
******************************
ORG $300
BELL EQU $FBDD
START JSR BELL ;RING THE BELL
END RTS
- hires byte patterns from keyboard input
******************************
* PATTERN KEYS *
******************************
ORG $0800
PATT EQU $FC
GRAPH EQU $C050 ; DEFINE SOFT SWITCHES
TEXT EQU $C051
MIXED EQU $C053
HIRES EQU $C057
PGONE EQU $C054
KEYIN EQU $FD1B ; LOCATION TO READ THE KEYBOARD
LSB EQU $FA
MSB EQU $FB
CHAR EQU $C000 ; INITIAL BYTE PATTERN
CLEAR LDA #$01
STA PATT
JSR DRAW
JMP KEYLOOP
SET LDA #$FF
STA PATT
JSR DRAW
KEYLOOP LDA CHAR
CMP #$80 ; CHECK FOR CHARACTER
BCC KEYLOOP ; WAIT FOR CHARACTER
JSR KEYIN ; GET KEY VALUE
STA PATT ; SET PATT TO KEY VALUE
CMP #$C3 ; CHECK FOR C
BEQ END ; END IF C
NOP
LDA $C010 ; CLEAR THE KEY STROBE
JSR DRAW
JMP KEYLOOP
ROTATE CLC
ROL PATT
BNE ROTRET
LDA #$01
STA PATT
ROTRET RTS
END LDA TEXT ; SET TEXT MODE
BRK
DRAW LDA #$20
STA MSB
LDA #$00
STA LSB
LDY #$00 ; TRIGGER SOFT SWITCHES
LDA GRAPH
LDA HIRES
LDA PGONE
LOOP LDA PATT
STA (LSB),Y
INC LSB
BEQ BUMPMSB
JMP LOOP
BUMPMSB INC MSB
LDA #$40
CMP MSB
BEQ RETURN
JMP LOOP
RETURN RTS
The PATTERN KEYS program docs/T.PATT_KEYS uses the value of the latest key pressed to set a hires pattern on the Apple II screen.
- Read the T.PATT_KEYS text file into the Merlin 8 Assembler
- Assemble the code
- Save the object file
- Call -151
- BLOAD PATT_KEYS
- 800G
The output will look like:
