Bruno Keymolen's C64 emulator project provides insights into the memory structure of the Commodore 64. Understanding this memory map is crucial for accurate emulation.
Memory Overview
Total Memory Range: 0x0000 to 0xFFFF (64KB)
Not all of this is RAM - some areas are mapped to ROM and I/O
Key Memory Regions
Kernal ROM: 0xF000 - 0xFFFF
BASIC ROM: 0xA000 - 0xC000
Screen Memory: 0x0400 - 0x0800
Screen Memory and VIC Chip
The screen memory (0x0400 - 0x0800) is particularly interesting for user interaction. Writing to this area affects what's displayed on the screen. For example:
POKE 1024, 49 // This will display the character '1' at the top-left of the screen
Bruno's implementation handles screen output using a basic ASCII mode, simulating the functionality of the VIC (Video Interface Chip) in its most fundamental form.
Emulator Implementation
In Bruno's emulator:
The full memory range is emulated
ROM areas are loaded with the original Kernal and BASIC
Screen memory writes are interpreted to update the ASCII-based terminal UI
The VIC chip emulation is simplified to handle basic text output
Try a Simple BASIC Command
10 FOR I = 0 TO 39
20 POKE 1024+I, 65+I
30 NEXT I
40 PRINT "ALPHABET PRINTED ON SCREEN!"