VTxx

VTxx refers to V.R. Technology’s “NES-on-a-chip” Famiclones, some of which having greatly extended capabilities. These capabilities are described in separate articles:

• VT01 STN Palette
• VT02+ PRG-ROM Bankswitching
• VT02+ Video Modes
• VT02+ CHR Pattern Data Layout
• VT02+ CHR-ROM Bankswitching
• VT02+ MMC3 Compatibility Registers
• VT03+ Enhanced Palette
• VT02+ Sound
• VT02+ Registers
• VT02+ Cartridge Connector

The progression of features as well as backwards-compatibility is contiguous until the VT09. The VT31 and VT368 are the lower- and higher-end enhancements to the VT09, are not compatible with each other, but are backwards-compatible to the VT09 except in the format of the enhanced palette and the absence of the second APU.

Subor uses a VT08 with standard NES functionality, and a similarly named VT06 was spotted in a handheld; its purpose or connection to VRT are unknown and unconfirmed. Jncota uses a VT38, based on a VT33.

The VT1682 and VT268 are not NES-compatible, even as their designs are inspired by it.

CPU $0000-$07FF: 2 KiB of internal RAM
CPU $0800-$0FFF: VT01-VT03: Mirror of CPU $0000-$07FF, VT09+: Further 2 KiB of internal RAM
CPU $1000-$1FFF: VT01-VT32: Mirror of CPU $0000-$0FFF, VT369: Embedded 4 KiB ROM
CPU $2000-$2007: RP2C02-compatible PPU registers
CPU $2010-$201F: VT02+: New PPU registers
CPU $2020-$207F: VT369: Newer PPU registers
CPU $3000-$3FFF: VT369: Mirror of PPU $2000-$2FFF, allowing direct nametable access
CPU $4000-$401F: RP2A03-compatible APU, DMA and I/O registers
CPU $4020-$403F: VT02+: New APU, DMA and I/O registers
CPU $4100-$41FF: VT02+: New miscellaneous registers
CPU $4800-$4FFF: VT369: 2 KiB of RAM shared with sound CPU
CPU $5000-$53FF: VT369: Mirror of PPU $3C00-$3FFF, allowing direct palette access
CPU $6000-$7FFF: Optional WRAM, if present on cartridge, VT369: Optional ROM bank
CPU $8000-$FFFF (write): VT02+: When forwarding is enabled (register $410B bit 3 "FWEN" =0):
                         MMC3-compatible registers that are forwarded to $4101-$4108)
CPU $8000-$FFFF (read): Four 8 KiB PRG-ROM banks.

CPU $0000-$07FF: 2 KiB of scratch RAM
CPU $1800-$1FFF: 2 KiB of RAM shared with main CPU
CPU $2000-$2FFF: Sound registers
CPU $4000-$4FFF: Embedded 4 KiB ROM

PPU $0000-$1FFF: CHR-ROM, all modes: CHR pattern data, bit planes 0 and 1
PPU $2000-$2FFF: NTRAM (2 KiB, selectable mirroring)
PPU $3C00-$3EFF: VT369: CGRAM in 8bpp modes
PPU $3F00-$3F1F: CGRAM in 2bpp modes, entries $3F10/$3F14/$3F18/$3F01 mirrors of $3F00/$3F04/$3F08/$3F0C.
                 VT03+: Also CGRAM in 4bpp modes, bits 0 to 5, of colors 00-1F; same mirroring of address bit 4 applies.
PPU $3F20-$3F7F: VT03+: CGRAM in 4bpp modes, bits 0 to 5, of colors 20-7F; no mirroring of address bit 4.
PPU $3F80-$3FFF: VT03+: CGRAM in 4bpp modes, bits 6 to 11, of colors 00-7F; no mirroring of address bit 4.
PPU $4000-$5FFF: CHR-ROM, 4bpp modes: CHR pattern data, bit planes 2 and 3 (VT03+)

The VT01 is V.R. Technology’s first Famiclone. Its only enhancement is the ability to drive an STN display directly using a modified palette.

The first of the V.R. Technology Famiclones to add major enhancements:

• OneBus mode: PRG and CHR data come from the same address space. The cartridge connector’s PPU Address lines are repurposed as higher-order Address lines.
• Integrated MMC3-compatible bankswitching by the console, active when in OneBus mode.
• Ability to use NTRAM as CHR-RAM.
• Choice of PPU A12 and HBLANK as a source for clocking the scanline interrupt.
• Automatic X/Y light gun position determination.
• Integrated RS232 interface.
• Direct NTSC/PAL and 50/60 Hz identification.
• Automatic per-attribute-tile background and per-sprite sprite bankswitching.
• DMA can be used to transfer data to PPU memory (via $2007) in addition to the normal transferring of data to OAM memory (via $2004).
• A second APU doubling the number of sound channels.
• Raw PCM output using full eight bits of resolution.
• DMA-driven raw PCM output.
• Data for DMA-driven DPCM/PCM output can be placed anywhere in CPU address space, not just within the $C000-$FFFF range.

• Removes the second APU and the RS232 interface.
• Adds a mechanism to automatically turn off the system after a set amount of time.

Based on the original VT02. The VT03 greatly enhances the graphical capabilities of the original RP2C02:

• Sprites can be 16 pixels wide.
• Graphics can use four bits-per-pixel, so that together with two attribute data bits, sixty-four rather than 16 colors each for background and sprites may be chosen.
• Enhanced color palette with twelve bits rather than six bits per color.

Low-cost replacement for VT03. Knowledge of its functions was reverse engineered using the VT16 and VT18 datasheets.

• Internal CPU RAM is 4 KiB rather than just 2 KiB, removing the need for additional WRAM for many applications.
• 4 bpp pattern data can be arranged in an alternative pattern that allows a single 16-bit fetch to retrieve two planes’ data, allowing the use of slower ROM chips.

Revision of the VT09 that offers an additional LCD controller.

Current major enhancement of the VT09 line.

• Hardware multiplier and divider.
• Enhanced palette format changed from the VT03’s saturation-luminance-hue-based to a simpler 12-bit (4-4-4) RGB format.
• Second APU is removed.

Popular revision of the VT31 with a new two-channel (AD)PCM engine, allowing playback independently of normal PRG banking.

Final enhancement of the VT09. Strictly this is not part of the VTxx line and instead of the VTxxx line, but it is backwards-compatible with the VTxx line.

• Hardware multiplier and divider.
• 5.37 MHz CPU mode.
• 8 bits-per-plane video modes.
• 30 fps video mode for slow ROM chips.
• 16x 8-bits-per-plane 16x16 sprites per scanline.
• Enhanced palette format changed from the VT03’s saturation-luminance-hue-based to a simpler 15-bit (5-5-5) RGB format.
• Additional sound CPU for arbitrarily-encoded multi-channel (AD)PCM playback.
• Second APU is removed.
• Additional additive outer bank register called “relative bank” that applies to all CPU/PPU ROM accesses.

Revision of the VT368; the additions that the chip was meant for are unconfirmed. Additions only confirmed to exist on this chip include:

• SD card support.

High-resolution version of the VT369, with a 512x480 video mode.

• Publicly-available datasheets on V.R. Technology’s website
• Archived copy of old V.R. Technology website containing VT31 information

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