After finishing the new design for my 7400 Logic Calculator, I continued to think about different ways to build a minimal design that would fit in a calculator body. Watching James Sharman's videos about his breadboard computer got me thinking about eliminating the microcode sequencer ROM, which would save a lot of room. It eventually dawned on me that the ALU ROM could be eliminated too if it was combined with the program ROM. ALU operations then become ROM lookups and can share the same circuitry used for looking up constants which also eliminates chips. Based on this, I came up with a modified design using only 18 chips compared to the other design's 21. Best of all, the whole thing fits into just one 32K EEPROM rather than three.
Saturday, July 30, 2022
Sunday, July 10, 2022
6502 Interactive Assembler
One of my 2022 Project Goals is a PIC32-based robot which emulates a 6502. While working on the emulation, I kept having to look up details about address modes and flags, so I made a Python program for Linux called i65 to look up information like the addressing mode, size, cycle count, and flags for 6502 instructions (GitHub link). It can take an instruction name or addressing mode as an argument and displays information for any instructions that match.
If the program is started without any arguments, it waits for input and shows all instructions that match what you type until it's narrowed down far enough to show the full information. The Kowalski 6502 simulator has this, and I wanted something similar for Linux.
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