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update readme with new info

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Amber
2020-05-26 13:58:10 -04:00
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README.md
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@@ -4,11 +4,13 @@
The bedroom Z80 will be a Z80-based microcomputer with an advanced I/O system, boot scheme, and graphics hardware:
- On boot, the coldboot ROM will search a FAT SD card for a bootfile, load it into RAM, and execute it. The bootfile will be a BIN file that contains code neccesary to boot. This bootfile can be copied and moved the same as any other file, allowing for easy backup and distribution of boot code. Due to a quirk in the way the Z80 (and CP/M) operates, once the ROM has finished its work, it will remove itself from the memory address space.
- On boot, the coldboot ROM will search a FAT SD card for a bootfile, load it into RAM, and execute it. The bootfile will be a BIN file that contains code neccesary to boot. This bootfile can be copied and moved the same as any other file, allowing for easy backup and distribution of boot code. Due to a quirk in the way the Z80 (and CP/M) operates, once the coldboot ROM has finished its work, it will remove itself from the memory address space.
- It will be able to recognise a signifigant number of I/O devices. One recognised, the I/O device will be assigned an area of I/O space, and a driver will be loaded to communicate with the device. There are 2 64k I/O areas, one will be used for general I/O and the other will be used to access the 64k of VRAM.
- It will come with 64k of RAM by default. There will be a basic MMU, using 16 2k pages in the upper 32k of RAM. The lower 32k will be static. The MMU will not be very useful unless a RAM expansion is installed. Up to 256 2k pages will be supported.
- The graphics system will be more advanced than most homebrew computer projects. It will have a custom TTL logic graphics card that will be able to display 320x200 in 256 colours, or 640x400 in 4 shades of grey over VGA. Possible other modes include 320x400 or 640x200 in 16 colours, from the 256 colour palette. These graphics modes all fit in 64k of VRAM, which will have a hardware double buffer.
- It will use a full 64k I/O space, using the upper 8 bits as a Device ID and the lower eight bits as a device address. This creates 256 I/O devices with 256 addresses each. This way, the device ID can be left in the upper address register, while the device address register is updated.
- The graphics system will be more advanced than most homebrew computer projects. It will have a custom TTL logic graphics card that will be able to display 320x200 in 256 colours over VGA. If possible, there will be a high res mode, at 640x400 in 4 shades of grey. There will be 64k of double-buffered VRAM, interfaced through a DMA chip on the card.
### Todo: