Notes: Controls: * Assemble - Assembles (compiles) the source code in the text box into 6502 object code at address $0600. Also performs a Reset. Any error messages appear in the info box at the bottom of the page. * Run/Stop - Runs (executes) or stops execution of the 6502 code. This button will be disabled when unassembled code exists in the text box (for example, if you add code, or if the code doesn't assemble correctly). Code stops executing when a BRK instruction is hit (which is the default instruction following your assembled code). * Reset - Rests registers, sets the PC to $0600, and clears the zero page, stack, and displays. * Hexdump - Displays memory contents from $0600 to the end of the assembled code, in hexadecimal format. * Disasseble - Display a hexdump plus a disassembly of the memory contents from $0600 to the end of the assembled code. Note: if the disassembled code does not match your source code after a Run, then your code has probably overwritten memory page $06 (and later) -- which is easy to do since this page immediately follows the bitmapped display. * Notes - Displays this information text in the info box at the bottom of the page. * Speed - Sets the speed of execution in instructions per display frame. Set to the left, the speed will be approximately 1% of a 1MHz 6502; on the right, it will be about 100% (or just over). * Save - Downloads the source code in the text box to your local machine. This is an easy way to make backup copies of evolving code, or to place the code in a file under version control. * Load - Loads the specified file from the local machine into the text box. This is an alternative to cutting and pasting code into the emulator. * Monitor - Displays the memory region starting at "Start" and running for "Length" bytes. * Text screen - Enables and disables the text display (on the right hand side). * Debugger - Turns on single-stepping controls. * Step - Executes a single instruction. * Jump to... - Jumps to the specified address or label. Memory map: All 64K ($0000-$ffff) is populated with RAM and available. This is the system memory map: Page $00: 6502 zero page, used for variables and pointers Two locations in the zero page are connected to devices: * Memory location $fe contains a new random byte on every read. * Memory location $ff contains the ascii code of the last key pressed. Values written to $ff will remain unchanged until next key press. Printable keys have their ASCII value; BackSpace is $08; Enter is $0d; Cursor controls are $80=up, $81=right, $82=down, $83=left Page $01: 6502 stack (downward) Pages $02-05: bitmapped display Pages $06-$ef: your code and data Pages $f0-$f7: character display Pages $f8-$fd: reserved for future ROM expansion Pages $fe-$ff: ROM code (see below) Available Assembler Directives: dcb value[,value [...]] - (define constant byte) used to create constants in memory. Multiple bytes are separated by commas. Values may be in decimal, hexadecimal, or single characters in double quotes (except spaces - use 32 or $20 to represent a space). define macro value - defines a macro expression. value must be an opaque string. *=address - changes assembler pointer to given address label: - defines an address label. Reference the label in your code without the colon. Labels can be used with the "Jump To" button in the debugger. Bitmap Display: The bitmapped display is 32x32 pixels, and memory locations $200 to $5ff map to the screen pixels. The lowest four bits of each byte set the colour of the corresponding pixel. The colours are: $0: Black $1: White $2: Red $3: Cyan $4: Purple $5: Green $6: Blue $7: Yellow $8: Orange $9: Brown $a: Light red $b: Dark grey $c: Grey $d: Light green $e: Light blue $f: Light grey Character Display: The character display is 80x25 characters in size, and memory locations $f000-$f7cf contains the ASCII characters on the display (row-major). Bit 7, if set, make a character appear in reverse video. Codes $21-$7e (and corresponding codes with bit 7 set, $a1-$fe) display; all other codes show up as blanks. ROM Routines: These routines are defined in ROM: * SCINIT $ff81 - Initialize and clear the character display * CHRIN $ffcf - Input one character from keyboard (returns A) * CHROUT $ffdw - Outputs one character (A) to the screen at the current cursor position. Screen will wrap/scroll appropriately. Printable characters and cursor codes ($80/$81/$82/$83 for up/right/down/left) as well as RETURN ($0d) are accepted. Printable ASCII codes with the high bit set will be printed in reverse video. * SCREEN $ffed - Returns the character screen size in the X and Y registers. * PLOT $fff0 - gets (CARRY=1) or sets (CARRY=0) the cursor position If C=0: X,Y registers set the cursor position Y:X is returned as a pointer to the current screen position If C=1: X,Y registers return the current cursor position A contains the character at the current cursor location To use these routines, these define directives may be pasted into your code: ; ROM routines define SCINIT $ff81 ; initialize/clear screen define CHRIN $ffcf ; input character from keyboard define CHROUT $ffd2 ; output character to screen define SCREEN $ffed ; get screen size define PLOT $fff0 ; get/set cursor coordinates Speed Slider: The Speed slider controls the number of opcodes executed per display frame. When set fully left, the emulator operates at about 1% of the speed of an actual 6502 chip; when set rully right, the emulator operates close to the actual speed of a 1MHz 6502 chip (depending on the code). It is recommended that the higher speeds be used with the ROM routines. References: A reference for the 6502 opcodes is available at http://www.6502.org/tutorials/6502opcodes.html Another reference with flag information: https://www.masswerk.at/6502/6502_instruction_set.html Example code which will run in this emulator: https://wiki.cdot.senecacollege.ca/wiki/6502_Emulator_Example_Code More examples, plus the ROM source code: https://github.com/ctyler/6502js-code Source code for this emulator: https://github.com/ctyler/6502js The emulator is licensed under the terms of the GPL v2. The code-bedder library is licensed freely (see https://codebedder.com) The prism.js library (https://prismjs.com) is licensed under the MIT license as follows: MIT LICENSE Copyright (c) 2012 Lea Verou Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.