Retrochallenge 2018/09, 2019/03
The Cat-644 is a computer I've been developing around an Atmega 644 microcontroller
- Started in 2013
- Atmega 644, 20Mhz, 4k internal SRAM (possibly upgradable to Atmega 1284 with 16k SRAM)
- 128k bitbanged SRAM: used as VRAM and XRAM
- VGA output, maximum of 64 colors at 512x240, software cycle-counted race-the-beam
- PS/2 keyboard
- RS-232 serial port
- SD Card
- 11 Khz mono 8-bit sound output
- expandable SPI bus: some experiments have been done with SPI-based ethernet shield originally intended for arduino
- It has been 'hardware complete' for a long time, and I have test programs for each piece of hardware, and combinations of hardware. (VGA + sound + keyboard all together was hard)
Wait, this computer project is only 5 years and, and it's made with a Microcontroller variant that's released in the 21st century. Does it not qualify?
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- The first AVRs were released in 1996, this is just a modernized version of the chip. (Counterpoint: the Intel i9 is just as vintage, as it is just a faster 8086.)
- This is built in the style of 8-bit home computers, with similar limitations: 128k of ram, 64 colors, 20 Mhz. (Emulated 16 mode w/ VGA running os about 250k instructions per second)
- True 8-bit operation. Not like those 'Altairduino' that used a 32-bit Arm.
- Microcontroller has a Harvard architecture and can't run native programs in RAM. User-mode programs will be written in an interpreter emulating a 16-bit processor. (Similar enough to Wozniak's Sweet16?)
- RS-232 communications, PS/2 keyboard, VGA monitor: None of this USB and HDMI rubbish!
- VGA is bitbanged via the microprocessor, only allowing blanking intervals for program operation. Certain operations glitch out the screen. (ZX80-ish)
- One the the first goals for a usermode program is a terminal emulator. This can at least be the dumb terminal for a real vintage computer
- If I don't start working on the OS soon, it will probably become a vintage computer before I finish it. (The hardare only took 5 years!)
- Exceptions will be made for exotica?
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