Save RAM hack for NEC handheld consoles

Adding same RAM support to TurboExpress and PC Engine GT

Similar projects worth following
I started this 5 years ago. It had been on and off back burner and recently I am getting close to completing the working prototype

Users who had PC Engine (the little white console) or the CoreGrafx (dark gray) had a few options for saving game progress from HuCard games rather than the password saves. Also saves were built in the CD system. Users with TurboGrafx-16 had either Turbobooster Plus or TurboCD. All Duo has save option built in. Unfortunately the handheld system PC Engine GT and TurboExpress never had any option at all. I’ve been burned trying to read password from tiny 2.5″ LCD screen and not getting the right letters so I wanted to have a built in save option.

original 1.x were to be place between controller PCB and the battery bay.  I had planned to get a flat cable to connect to the cart connector but the space is narrow. A custom FFC was doable but it's rather pricey for a small run and with no guarantee it'd work, placing a larger order to reduce per cable cost wasn't worth the risk.  

I changed and went to have the board mount directly off the cart connector, became version 2.0. With thinner PCB, there was just enough space to make this work.  Currently I am on revision 2.1

Since the non-volatile memory chip did not come smaller than 8KB, and the original save support was designed for 2K, I decided to exploit the extra memory by having optional switch added to change the 2K section.  The board can have 8K (2 switches) or 32K (4 switches or 1 hexadecimal switch). Or they can be left as is, locked to 2K only.

Version 2.0 didn't work because I made a mistake.  The difference between TurboExpress and PC Engine GT is the pin D0 to D7 is flipped, a form of region lock. I ordered the TurboExpress version for my PC Engine GT, the board was basically getting gibberish and couldn't work at all.  Oops...  I thought about cutting off and hand wiring those 8 lines but it's a bit tricky in the limited space, I opted to wait a couple weeks for new boards instead.

More to follow when my 2.1 arrives, is populated, and tested.  I've attached the latest version of PCB and schematic from Eagle if you want to risk your handheld and play with it or clean up my messy schematic.  The PCB is likely the final version and will not see any more changes.  I changed PCB's via setting to be all covered since I don't need exposed via for testing or bodge wiring.  I'll upload standard gerber files later.

Note: about HuC6201 chip made by Sharp for Hudsonsoft/NEC.  They are found in Tennokoe Bank II and possibly other save devices. At the time I had found some suppliers that had NOS supply and attempted to contact them about pricing and ordering. 2 replied they are out of stock even though their web sites said they had some.  Other suppliers have not responded at all, maybe they don't know English? Someone help me?  Tennokoe Bank II is about $30 on eBay and limited in supply.  I do not have any other info on this chip other than the pinout or I would have gotten someone to make a clone of it in FPGA.

TE sram board 2.sch

Eagle schematic design for TurboExpress

sch - 472.63 kB - 06/01/2021 at 04:47


GT sram board 2.brd

Eagle board design for PC Engine GT

brd - 271.72 kB - 06/01/2021 at 04:47


GT sram board

standard gerber files for PC Engine GT board

x-zip-compressed - 125.71 kB - 06/01/2021 at 04:47


TE sram board

standard gerber files for TurboExpress board

x-zip-compressed - 124.53 kB - 06/01/2021 at 04:47


TE sram board 2.brd

Eagle board design for TurboExpress

brd - 269.00 kB - 06/01/2021 at 04:47


View all 6 files

  • Still working on it (try #3)

    killua06/01/2021 at 05:39 0 comments

    Another update: I discovered 2 of the address lines were flipped somehow. Corrected and reuploaded the Eagle files and gerber files.

    I also modified the proto board by swapping the 2 reversed address lines.  I am still not getting it to work at all.

    I am going nut!!!  I've checked and rechecked all the pins from the original Tennokoe, rechecked that they all were correct, all connected with SRAM as well.  Games still reports no save support at all.  I've looked at the schematic of TurboGrafx-16, there is no buffer chip or additional parts between cart pins and expansion pins, both sides are wired straight through.

    One thing to note though if you are trying this, there is one more thing I forgot to mention.   Tennokoe II has CDD pin on expansion port pulled to ground. They are floating high when there's no device connected to the system.  CDD pin is not present on cart slot and aren't used on TurboExpress or PC Engine GT. You need to find pin 30 of HuC6280 CPU (the chip one closest to cart ribbon cable) and lift it then short it to ground.  The RF shield hole nearby is grounded and would work with a short jumper wire. 

  • Still working on it

    killua05/18/2021 at 09:38 0 comments

    Still no luck on getting this to work.  I've reuploaded some files. Schematics were cleaned up the best I can. PNG of top and bottom layers, Eagle files, and gerber files added.

  • Another PCB revision came in, more testing and more hair pulling

    killua05/02/2021 at 04:21 0 comments

    I got the new board installed and checked, it did not work.  I double checked that the solder is making connection to the board from the cart connector.  (vias will be covered in final version)

    When I used BRAM tool, it reported no BRAM.  When I used TurboGrafx-16 CD System 2.0 card to access memory backup, I got corrupted display instead.  When I used PC Engine CD 2.0 card for the same thing, I was able to enter BRAM area to delete and format but the text is corrupted.

    I need to find my microscope to verify all the pins on HuC6201 is soldered and not accidentally floating.  The game I selected at random played fine with the board installed so there's no interference.  If those microscope check didn't find any error, I'd need to try a second HuC6201 chip I have to rule out defective chip.

    I really wish there were more documentation on HuC6201 beside the pinout, it'd be so much easier to troubleshoot this or clone the chip with FPGA or something similar.

View all 3 project logs

Enjoy this project?



Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates