Coin-Op Collection Presents: Midway T-Unit DCS (MiSTerFPGA)

Tonight's release for the MiSTerFPGA platform covers Williams/Midway's T-Unit arcade hardware, with Mortal Kombat II (1993) arriving at the Patron Beta tier as the platform's debut title.

T-Unit serves as the direct evolution of the Y-Unit design covered in the previous post, retaining the Texas Instruments TMS34010 graphics processor while introducing two new hardware blocks. Mortal Kombat II is the first arcade title to use the Williams Digital Compression System (DCS), built around an Analog Devices ADSP-2105 DSP and replacing the analog ADPCM and CVSD paths used on Y-Unit. Alongside the new audio architecture, T-Unit ships with an updated DMA chip that adds X/Y scaling, variable bits-per-pixel, edge clipping, and y-flip support, capabilities the Y-Unit DMA path could not handle.

Mortal Kombat II was designed by Ed Boon and John Tobias for Midway, with composer Dan Forden returning to score the soundtrack. The sequel expanded its roster with Baraka, Jax, Kitana, Kung Lao, and Mileena, alongside the hidden fighters Jade, Noob Saibot, and Smoke. Each character received multiple fatalities, and the entry added Babalities, Friendships, and stage-specific fatalities to the series, paired with a noticeably faster gameplay pace and a deeper system for combos and juggles.

It became America's highest-grossing arcade game of 1994 per AMOA data, with approximately 27,000 units sold over its lifetime against an industry benchmark of 5,000 units for a top-tier AAMA release, and grossed roughly $600 million in arcade revenue.

This post covers a brief technical overview of the T-Unit platform, the new DMA and DCS implementations, an update on the licensing portal introduced with the prior release, and the proposed schedule for upcoming Midway titles on MiSTerFPGA.

Licensing:

The licensing portal introduced with our last release remains the entry point for registering devices and managing keys. Keys are generated on the 2nd of each month, so existing patrons will need to generate a new key for May from the licensing portal.

Today's release launches at the Patron Beta tier, and if the core is run on a device that is not registered to a valid member, a QR code pointing to the Help page will appear on screen.

A few clarifications coming out of the prior release:

• Integration with the MiSTerFPGA updater is coming soon, with support from its author/maintainer theypsilon. I'll follow up with more information regarding our integration later this week.

• Starting June 1st, Coin-Op Collection releases within that month's window will continue to be valid and receive updates if a supporter is no longer a member. The end-user is responsible for saving their license, as they will no longer be able to generate keys.

• The projected public release window for beta/alpha cores is 30 to 180 days depending on project scope, remaining core functionality, and any open issues. Some new releases may be public on launch, and cores publicly available through the MiSTerFPGA updater are being ported to the K3 framework to meet my current standards. This porting work is projected to be complete no later than July 31st.

Overview:

The T-Unit hardware is built around the TMS34010 clocked at 50 MHz, with the video system outputting 400x254 visible at an 8 MHz pixel clock. The DMA adds X/Y scaling, variable bit depth from 1 to 8 bits per pixel, edge clipping on all four sides, and y-flip support. These additions enable the larger and more animated character sprites that define today's release.

The DCS sound board centers on the ADSP-2105 DSP at 10 MHz. The DSP runs compressed audio routines from on-board program RAM, streams audio output through its SPORT1 serial port to a DAC via auto-buffered DMA, and communicates with the main CPU through a host interface with input and output latches.

T-Unit hardware also ships in an ADPCM configuration similar to Y-Unit, retaining a 6809 driving a YM2151 alongside an OKI M6295 ADPCM decoder. The T-Unit ADPCM variants will be covered in future releases.

Development Challenges:

The headline development effort for this release is the Digital Compression System sound board, written from scratch as a full Analog Devices ADSP-2105 DSP core with all of its supporting logic for program and data memory, host interface, and the SPORT1 serial path driving the DAC output.

The second-generation DMA chip on T-Unit was also written to support the new graphics features the platform introduces. The block handles X/Y scaling at 8.8 fixed-point precision, with independent step values applied per pixel as the engine walks the destination raster.

Source data can be unpacked at any bit depth from 1 to 8 bits per pixel, with pre-skip and post-skip parameters allowing scanlines to start and end mid-byte for compressed sprite formats. Clipping operates on a rectangular bounding box defined by independent top, bottom, left, and right limits, and y-flip can be applied per-blit. None of these capabilities existed on the prior Y-Unit DMA path.

The TMS34010 main processor and the proprietary memory controllers introduced in the Z/Y-Unit release carry forward unchanged. The same fast SDRAM region-based path holds program ROM, graphics ROM, and main RAM, while DDR3 backs the live VRAM that the TMS34010 and the new DMA operate against in parallel.

Core Options / MK2+ Support / Known Issues:

The core exposes a shared set of video and audio controls alongside its own game-specific menu. Similar to the Z/Y-Unit releases.

Video options cover aspect ratio selection between original and full screen with two user-defined arcade ratios, vertical scaling between fill and integer modes, a force scandoubler toggle, and five scandoubler effects ranging from off through four CRT intensities.

Audio options reflect the DCS architecture and differ from the Y-Unit layout. A single DCS Audio toggle enables or disables the entire sound board, with separate triggers for DCS Volume Increase and DCS Volume Decrease in place of the per-channel mixers used on the analog Y-Unit titles.

Game settings include a Player 1 mapping swap, a synced mapping mirror for Player 2, and independent auto-fire per player covering Off, HP, LP, HK, LK, or All with rate selection.

The cheats block on this release is the most extensive set of in-core cheats shipped to date and is built entirely from full ROM disassembly work on Mortal Kombat II Rev L3.1. Every cheat is implemented as a runtime ROM or RAM patch with its own enable gate, and none of this functionality is currently available in emulation.

The basic toggles include Kombat Zone select for all ten tournament stages, per-player infinite energy, infinite time, infinite fatality time, hitbox display as a training aid, EJB menu enable to expose the hidden diagnostic screens, and CPU throwing disabled.

CPU behavior controls add a fixed CPU AI difficulty pin from 0 through 9 that overrides the stock difficulty ramp and the boss-floor minimums, alongside a CPU Fatality Type selector covering CPU AI, CPU Random, and Stage Only modes.

The finisher cheats let any character pull off their finishing moves from a single button press during the FINISH HIM / FINISH HER window, with HP firing Fatality 1, LP firing Fatality 2, BLOCK firing Babality, and HK firing Friendship. Stage Fatality (Auto) maps DOWN+HP to the stage-specific finisher on Pit II, Kombat Tomb, and The Dead Pool. Match-play special moves are preserved through gating logic that restores original ROM behavior outside the finisher window.

A companion document detailing every cheat, the per-character finisher table, and the cheat interaction notes will be made available as a PDF alongside this post.

DIP switches and a service menu access are also provided in the OSD. Once you've set your preferred settings in the CMOS menu and exited back to the title screen, you can save them by clicking save setting in the OSD.

MK2+ is supported, an alternate MRA is provided. You will need to do the remaining research to stand-up it's support. I have not had time to do extensive testing with MK2+ or the cheats that I have in place. They may differ as MK2+ is a modified revision of the game. For more information about the project, click here.

There are a few known issues with today's release, RAM chips fail in post-check, there is image flashing when the selected character ending plays and a few stray pixel lines in attract mode, the ladder, and stages that were introduced with the extensive options. I'll address these and publish an update as soon as they are resolved. Everything moving forward is solely about optimization for the MiSTerFPGA and PocketFPGA platforms.

Updates:

Several public, beta, and alpha releases will go out from today through next Saturday on both the MiSTerFPGA and Analogue Pocket platforms.

Over the weekend, an update for the Z-Unit and Y-Unit cores will publish, rotating the alpha titles from the previous release up to the beta tier and introducing new alpha entries on those platforms.

Thank you to all of our existing members for the continued support, and a warm welcome to everyone who joined Coin-Op Collection following the Z-Unit and Y-Unit releases. The response over the past few weeks has been beyond what I expected going into this transition, and your support is what allows this scale of work to continue.

I'll have more information about current and future projects published throughout this week's scheduled releases. Have a great weekend and enjoy!

Disclaimer: All product names, trademarks, and registered trademarks mentioned are the property of their respective owners. "Analogue", "Analogue Pocket", "MiSTer", "MiSTerFPGA", "OpenFPGA", "Williams", "Midway", "Mortal Kombat", "Mortal Kombat II" and all derivative works are trademarks, registered trademarks, or copyrighted materials of their respective holders. Use of these names does not imply endorsement or association with this post. All rights reserved to their respective owners. This post is for educational and research purposes only.