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unexpected eof while reading","robots_txt_status":"success","robots_txt_updated_at":"2025-07-24T06:49:26.215Z","robots_txt_url":"https://github.com/robots.txt","online":false,"can_crawl_api":true,"host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":[],"created_at":"2024-11-15T22:37:02.653Z","updated_at":"2026-01-26T20:14:20.839Z","avatar_url":"https://github.com/anachrocomputer.png","language":null,"funding_links":[],"categories":[],"sub_categories":[],"readme":"![Static Badge](https://img.shields.io/badge/CPU-MC6809-green \"CPU:MC6809\")\n![Static Badge](https://img.shields.io/badge/CAD-KiCAD_8-green \"CAD:KiCAD 8\")\n\n# Octuplex #\n\nA 6502/6809 microcomputer in the shape of an octagon.\n\n## Microprocessor ##\n\nA choice of two classic 8-bit CPUs, the 6502 or the 6809.\nThe two chips have similar pinouts and are placed on the PCB overlapping.\nOnly one chip may be installed at a time.\nClock speed 2MHz in both cases,\nwith the 68B09 requiring a 4x clock input,\ni.e. 8MHz.\nThe Hitachi 63B09 may also be fitted.\n\n## Timer ##\n\nThe standard Motorola MC6840 timer chip.\nCan generate interrupts and/or PWM signals.\n\n## Parallel I/O ##\n\nThe standard 6522 parallel port chip.\nCan generate interrupts.\n\nTwo handy little circuits for additional 8-bit I/O with minimal pin count: 74LS259 and 74LS251.\nThe 74LS259 is an unusual chip, an addressable latch.\nIt takes three address input pins and a single data input pin,\nand has eight output pins.\nThe 74LS251 is an eight-input multiplexer with tri-state output.\nThe selector inputs are connected to three address pins,\nwhile the output is connected to data bit D7.\nThe 6502's BIT instruction can read D7 directly into the sign flag,\nwhich can be followed by BMI or BPL.\n\n## Analog I/O ##\n\nThe classic Ferranti ZN428 8-bit DAC chip.\n\nThe classic Ferranti ZN448 b-bit ADC chip.\nAlthough I'm not sure about this one due to its need for a negative supply rail.\n\n## I2C Bus ##\n\nClassic Philips PCF8584 I2C bus controller.\nCan generate interrupts.\n\n## Async Serial I/O ##\n\nRockwell R65C52 dual ACIA.\nCan generate interrupts.\n\nMotorola MC6850 with optocoupler for MIDI.\nCan generate interrupts.\n\n## Display ##\n\nTBD, most likely an LED starburst display of some kind.\n\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fanachrocomputer%2Foctuplex","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fanachrocomputer%2Foctuplex","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fanachrocomputer%2Foctuplex/lists"}