About

This is a little hex-editor, specifically for hacking the text content of Commodore 8-bit PRG files.
E.g., for porting a program to an other language or patching up a program.
The edditor supports various Commodore-specific text encodings as well as US-ASCII (7-bit).

Instructions

• Drag&drop a PRG or BIN file or an 8-bit hex-dump onto the code field.
  Alternatively use the file upload button. — Do not paste!
  (Leading 4-hex-digit addresses and comments will be stripped from hex-dumps automatically.)
• The start address will be extracted automatically for PRG files. Otherwise, you will be prompted to enter a start address. (In this case, the start address is used for the listing only.)
• Select a text encoding. (The code field will update automatically).
• Find the text or hex-digits to replace.
• For text, enter the replacement text into the text box at the right, click “Transform”, and copy any hex-values from the output to the respective place in the code field.
• Click “Update” to commit any changes.
• The checkbox “guard file size” prohibits edits from accidentally altering the file size.
• When done, click ”Export” to download the resulting PRG or binary file.

Notes

• The modifier helps with simple, modular ecnryption schemes: any modifier is applied before the text decoding in the code listing and the inverse operation is applied to character codes in the transform box.
  E.g., if a program adds $B1 to any screen codes before transferring them to the screen memory, you’d want to use the character encoding for screen codes with a modifier of B1 and use the "add" operator.
• In case you wouldn’t know what Commodore old character ROMs and new ones are: early PET 2001s had the upper-case letters in the unshifted position and lower-case letters in the shifted position, but this changed soon, as Commodore swapped those characters in the character ROM. If it’s not about an early PET program, you want the new character ROM options.
  Generally, with any of the Commodore options, letters are shown as they would appear in the mixed case (lower-case/upper-case) mode.

Mind that this is a just simple hex-editor with additional tools for Commodore 8-bit specific text transformations. Other than checks for the file size, no further checks or adjustments are made and the code will be updated and exported as-is.
In other words, this tool supposes that you know what you are doing — no training wheels provided.

Disclaimer

This application is provided for free and AS IS, therefore without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. Use at own risk.

This application uses either Web Storage technology or, if this is not available, a cookie to store your choice for the preferred color mode for the virtual 6502 suite of applications. (Either the word "light" or the word "dark" is stored.)

© Norbert Landsteiner 2023, mass:werk