Saturday, September 12


Phantom Nine

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The Phantom Nine is a 9/18 bit home computer introduced in November 1986 to compete with the increasingly popular MSX systems.  The Phantom's 12MHz Y90 CPU is a rare variation on Zilog's Z80: All word sizes are increased from 8 to 9 or from 16 to 18 bits as appropriate, but the instruction set is largely unaltered and Z80 assembler code can be ported to the Y90 with minimal effort.

The Phantom Nine boots from an internal 2.2M 3½" floppy drive, having only 8k of ROM for boot code, a basic font, and a simple machine-language monitor.

This is because the Phantom does not support address extension, segmentation, or bank-switching; its 18-bit address space is fully populated by 256k of standard RAM.  The boot ROM itself is only mapped into address space long enough to copy itself into high memory.

The Phantom Nine features five custom chips:
  • Two video display controllers each with 64k of RAM, displaying 240x270 in 512 colours or 480x270 with two 16-colour palettes.  Each video controller supports any combination of scrolling, scaling, shearing, and reflection of the pixel map.
  • One sprite controller with its own 64k of RAM, supporting up to 600 8-colour 18x18 sprites.
  • One video mapper that combines the palette and priority selectors and pixel data from the video and sprite controller chips, and merges them into a single display.  The video mapper includes 96 colour registers shared by the video and sprite controllers.
  • One sound controller with its own 64k of RAM, supporting 9 voices of FM or PCM sound.

The video controllers have no hardware acceleration for drawing graphics; instead the Y90's block mode operations are used via the VDC interface registers to move or copy data.

The Phantom Nine received one major hardware update, in 1988.  The Phantom 9/512 has 512k total RAM, the extra 256k functioning by default as a RAM disk, though it can be directly addressed by the Y90's I/O instructions, allowing it to be used as heap space (for example, for Basic program variables) though not for executable code.

The 9/512 also includes an extended-density 4.4M floppy drive.

Unusually for systems of this era, the Phantom Nine never officially ceased production.  The parent company still sold new stock Phantom 9/512 systems on their website as of July 2019, with the choice of either the original 4.4M floppy drive, or an SD card reader and USB adaptor that fits into the floppy drive bay.

This adaptor uses a 48 MHz Arm microcontroller to interface the USB and SD card signals with the onboard floppy controller, meaning that it is significantly more powerful than the Phantom Nine itself.

A much later pin-compatible Y99 CMOS microcontroller running at 24 MHz can be swapped into both Phantom models with no other modifications required; the clock speed is selected by a previously unimplemented instruction sequence.  The Y99 supports numerous additional instructions and also executes many existing instructions in fewer cycles, while drawing approximately one-fifth the power of the original Y90 chip.

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Posted by: Pixy Misa at 02:53 PM | Comments (2) | Add Comment | Trackbacks (Suck)
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1 Hrm, well, I know that CDC and DEC had 36-bit processors, and as a good friend of mine once said, "There's nothing magical about powers of two."

Posted by: normal at Monday, September 14 2020 01:12 PM (obo9H)

2 Several PDP models, including the original PDP-1, had 18-bit words, and others had 12-bit words.  The only one I couldn't find an example of is a 10-bit architecture, though there are 20-bit and 40-bit systems.

Well, I didn't look for 13-bit systems.

Posted by: Pixy Misa at Monday, September 14 2020 02:23 PM (PiXy!)

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Apple pies are delicious. But never mind apple pies. What colour is a green orange?

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