Lab Updates and Posts
SMS Flash Carts - Function SRAM Save Feature
 I picked a game which supported SRAM saves, Phantasy Star (english SMSPower translation) because this particular version has the FM soundtrack unlike the english North American version. On my first test, the save feature didn't work; turns out I had forgotten to assign the SRAM WE pin on the CPLD (always assign your pins!). After this quick fix it worked like a charm! I guess it shouldn't be surprise, this mapper is about as simple as VHDL design gets. However, one challenge will be to pack a bank-shift feature (to allow for multi-rom carts) inside the EPM3064. This particular CPLD is limited to 64 macrocells; enough for the Sega Mapper implementation, but maybe not so for bankshifting. Next I need to test an all new exclusive feature - saving to serial EEPROM. No Sega Master System as far as I know did this, and logically, only new homebrew written with the serial EEPROM in mind could exploit the feature. Using the serial EEPROM greatly increases the available save memory and reduces costs at the same time. |
dbGrafx Booster - Red, Green, Blue, Chroma, Luma - Oh My!
 Last night I assembled and tested two variants of the new design: one CXA1645 based, and one THS7314 based. The major difference between these two video chips is that the CXA1645 can transcode S-Video while the THS7314 is a simple video amplifier. I chose to make compatible with two video chips in case the CXA1645 didn't pan out since it's an older chip. After a few minutes of testing and comparisons, it was clear that the CXA1645 design was superior. Not only is the addition of S-Video a huge bonus for gamers where SCART was not standard, but the quality of the RGB signal was much better in my opinion. I don't really have the video capture equipment to make a good comparison so I guess you'll all have to trust me on that. That being said, the dbGrafx Booster will be built and sold with the Sony CXA1645. Stay tuned for updates to availability of the dbGrafx Booster. |
Mark III FM Power Base Converter - Complete!
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SMS Homebrew CPLD Firmware Looking Promising!
 Anyway, to address this, Sega produced what is known as the Sega Mapper which allows banks of 16KB to be swapped in and out of the available 48KB ROM space. Using this technique allowed games up to 1MB to be produced for the Master System. Part of my challenge in getting the SMS Homebrew Cart working was to reproduce the Sega Mapper in VHDL on a EPM3064 CPLD. While this is not a particularly difficult task VHDL wise, it was slightly time consuming owing to errors I made on the first batch of PCBs (always check if your ground plane is present before sending PCBs to manufacturing!). My first functional mapper has proven successful in running the Sonic FM hack. Source code for my first functional mapper can be found on GitHub. |
MD Flash - Hardware to Release Physical Megadrive / Genesis Games
 Anyway, back to the topic at hand. I decided to use purely 5V parts to avoid any kind of out-of-spec condition in my product. The result: a 16Mbit max (2Mbit, 4Mbit and 8Mbit available as well) with 32KB of save RAM (FRAM or battery-backed SRAM). The Flash parts used are MX29F800 (or MX29F400 - MX29F200) and save RAM is FM1808 (FRAM) or AS6C62256 (SRAM).
Not An Everdrive!MD Flash is NOT an Everdrive nor is it trying to be an Everdrive. MD Flash is modern cart hardware which can be used to release new games in a 5V safe way which gives developers peace of mind about not running the Megadrive / Genesis bus out of spec into clamping diode hell!
Burning the ROMsI've been using a TL866CS EEPROM burner for some time now and have no real complaints about it. This burner has native support for MX29Fx00 parts so I decided I was not going to re-invent the wheel and would not make custom burning hardware. Instead, I simply designed a cartridge adapter which plugs into the TL866CS and converts the 64-pin Genesis cartridge into the 44-SOP pinout for MX29Fx00. There is a jumper on my cartridge adapter to select between upper 8Mbit and lower 8Mbit when my cart is configured for 16Mbit ROMs. EndiannessThe Motorola 68K CPU is a Big-Endian CPU which means that ROM files you have (but legally shouldn't ;)) on your PC are not compatible to be directly burned onto MD Flash. The high and low bytes of each word must be swapped. For this, I wrote a quick C# Endian Converter which swaps all bytes in each word and also separates the ROM into two 8Mbit files (upper and lower) if the ROM is larger than 8Mbit. The output files from my Endian Converter can be directly burned onto MD Flash.
ResultsHow to Release GamesIf you're interested in releasing a game on Genesis / Megadrive using the MD Flash hardware, stay tuned to updates on my Products page where I will put up a product page for MD Flash shortly. Exact details on burning arrangements will be worked out on a customer per customer basis. I will absolutely NOT burn repros for you, it must be an original game. |
UMDK
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dbGrafx Booster is CSync'ing!
 I tried a few circuits with NOT Gate amps to produce a quick and very low delay Sync pulse but nothing seemed to operate to my liking. Finally, I decided I was fighting a losing battle and decided to order a few LM1881 sync separators. These are purpose-built chips which take in the CVBS video signal and output a TLL CSync pulse - DONE! I simply built the exact circuit found on page 7 of the datasheet and it works flawlessly (as it should!). Now, the next step is to pull out my RGB to SCART gear and test if this will pass the test - stay tuned! |
dbCard Functional Prototype With 3D Printed Plastic Holder
A few months ago I announced dbCards which are release HuCards for homebrew software (dbCard (TurboGrafx-16 Homebrew Flash Cart) Prototype Fully Working). While this was great, the form-factor was wrong. It just didn't look like a HuCard. Therefore, I set out to design a second prototype which would have the look and feel of a traditional HuCard.
I designed a plastic holder using FreeCAD and had a few prototypes 3D printed. Then, I designed a PCB which would, in conjunction with the plastic holder, form an equivalent to a HuCard. There are two pockets in the plastic holder: the first pocket is the depth of the PCB and the second pocket is the depth of the components on the PCB. As can be seen in the pictures below it all fits together quite nicely!
Being constricted to the HuCard mechanical shape makes it harder to burn software onto the dbCard. Currently, I simply pre-burn the TSOP48 Flash ICs in my TL866CS before soldering them. For the future however, I do have plans to burn the chips only after they have been soldered by using a programming header which I've populated on the dbCard PCB. Here's a quick video showing a working dbCard!
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Mark III FM Power Base Converter Prototype
 Before I invest time in branching a FM Power Base Converter design to a Mark III edge connector, I figured I should first try to get it working by hand-soldering a 44 pin 0.125" edge connector to one of my FM Power Base Converters. This was "almost" as simple as connecting the same-named signals together. There was however a few exceptions. On Power Base Mini and FM Power Base Converter:
On M3 Power Base Converter prototype
 I have to thank the great people at SMSPower.org, specifically in this thread, which provided very good information about some errors in online Mark III pinout documentation. Now that I have a proof of concept, I'll start a branch of the FM Power Base Converter to support Mark III games. What's nice about this is that, because the Megadrive/Genesis doesn't use a BIOS like the Master System, there should be no issues with play any/most of the Mark III library on Megadrive/Genesis. Hooray for imports! You can get a suitable Mark III edge connector from Sullins, part# EBA22DCTN. |
Genesis Game Cart Current Consumption Measurements
In attempting to figure out what the maximum "safe" amount of current to draw from the cartridge port is, I thought a good experiment would be to measure the current draw of existing games. I used one of my new Genesis Probing Adapters to easily measure the current each of these game carts requires to operate. Pictures of the experiment are here, and a table of results can be found in Technical Info along with other Genesis power supply information. The choice of which games to measure seemed obvious to me.
ResultsIn my opinion, the current consumption values measured on Virtua Racing are probably a good limit to follow. If we consider that all of the cartridge current is supplied by a +5V LDO, then an additional 100mA (drawn by Virtua Racing) is probably starting to push the limits of a poor old LM7805. Behold the towers of power! |
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