4 ms·
The Commodore 64 has a similar "feature". It has a separate 4-bit per address * 1k "nibble" ram chip for the screen color attributes. The processor and data b
by dzdt 5y ago
The Commodore 64 has a similar "feature". It has a separate 4-bit per address * 1k "nibble" ram chip for the screen color attributes. The processor and data bus are 8 bits wide. When the processor reads from color ram the low 4 bits come from the color ram chip but the hi 4 bits are disconnected. The returned results look a bit random but are actually whatever data was put on the bus the previous clock cycle.
- mananaysiempre 5y agoWell, the OSDev Wiki’s discussion of RAM detection on x86[1] still mentions the issue of bus capacitance in its discussion of memory probing (while exhorting you not to attempt memory probing). The text is likely old, but probably not C64 old. Pentium-era old maybe? [1] https://wiki.osdev.org/Detecting_Memory_(x86)#Practical_obstacles_to_memory_probing https://wiki.osdev.org/Detecting_Memory_(x86)#Practical_obst... and https://wiki.osdev.org/Detecting_Memory_(x86)#Manual_Probing_in_ASM https://wiki.osdev.org/Detecting_Memory_(x86)#Manual_Probing...