amberisvibin/chibi-pc09
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2025-08-01 07:59:28 -04:00
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# chibi pc-09 # chibi pc-09
![GitHub last commit](https://img.shields.io/github/last-commit/amberisvibin/chibi-pc80) ![GitHub last commit](https://img.shields.io/github/last-commit/amberisvibin/chibi-pc09)
## Description ## Description
The PC-09 will be a 6309 based microcomputer with a 74LS612 MMU, uPD72020 graphics, PS/2 keyboard and mouse input, and a capable UART. The PC-09 will be a 6309 based microcomputer with an MMU using 74HC670 register files and dual 16550 UARTs. The plan is to eventually add uPD7220 graphics and PS/2 mouse and keyboard.
The MMU will allow up to 2 megabytes of I/O to be paged into the address space. Pages are 4k. System storage will be paged into the address space as well, as it will be either EEPROM or flash. The two 74HC670s will take the top 4 bits of the address bus and expand them to 8 bits, turning the 16 bit cpu address space into a 20 bit address space capable of addressing 1MB of memory. Memory pages are 4KB. Being a register file, any page can be mapped to any slot, allowing complex memory management schemes.
The uPD72020 is a very advanced graphics chip for it's time, capable of accelerated drawing of lines, shapes, fills, and characters. It can be coerced into outputting a VGA signal at 640x480 and *maybe* 800x600. The 16550 UART is capable of interrupt driven operation with FIFOs, allowing for characters to be processed in batches rather than individually, minimizing task switch delays. They also support hardware flow control, and some versions can automatically assert RTS when the FIFO is nearing full.
Keyboard and mouse will be handled by the VIA VT82C42. It is an Intel 8242 compatible controller capable of both PS/2 keyboard and mouse. It's interface is relatively simple, which makes connection easy. It relies on interrupts, so an interrupt system will be required. The uPD7220 graphics are very powerful, allowing 16 colors at 640x480, but it is a complex chip to get working. It will be left for a later date.
To avoid the infamous 65C22 bug, the system will use the 16550 UART from the PC ecosystem. It is *relatively* easy to interface this to a 6800 style bus. It has more features than a 65C22 as well. As configured, it will be stable up to 38,400 baud. The solution for PS/2 keyboard and mouse have not yet been decided.
## Progress ## Progress
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The PCB and parts for Prototype #1 have been ordered, and assembly will begin soon. Initial test code is now available in the code/ directory. The PCB and parts for Prototype #1 have been ordered, and assembly will begin soon. Initial test code is now available in the code/ directory.
Assembly is in progress.
## License ## License
This project is licensed under the MIT license. This applies to both the hardware (schematics, bill of materials, pcb layouts) and documentation. This does *not* apply to the datasheets/ directory, the books/ directory or code/assist09/. Those files belong to their respective copyright holders. This project is licensed under the MIT license. This applies to both the hardware (schematics, bill of materials, pcb layouts) and documentation. This does *not* apply to the datasheets/ directory, the books/ directory or code/assist09/. Those files belong to their respective copyright holders.