CCAM - Crystal Clear Audio Mod for Sega Genesis/MegaDrive by Tiido

I took an afternoon to look at Tiido's circuit to clean up and amplify certain channels on the poorer created versions of the Sega Genesis and megadrive. This circuit separates all of the audio channels, amplifies them individually, mixes, amplifies again, offsets the DC output and applies a low pass filter. This is based on the sound filter inside of the original "HD Graphics" models of the sega genesis which arguably has the best sounding output.

I have taken the liberty of redesigning the circuit with all higher quality 1% tolerant, through-hole components, a low power op amp and easy to solder tie points for installation.

Fun with the Sega Genesis - Ultimate Portable Game player

Found a crazy deal on fleabay for one of these and had to have it. I had heard stories of how badly they are made, and how miserable the audio is.
All very true, but I think it can be improved a little.

The video is great, the size a too small, the sound from the speaker is crap but the sound from the headphone could be worse.
I immediately took it apart after opening the box. I was THRILLED to see only one epoxy-chip and several SOP's! :D

I want to believe that the audio issue is because of the amp/filter they have used. Through headphones, it sounds ok, but also a little clipped and shallow. This could also be because of the power supply, which is very weak. The battery is 3.7v and droops when the PSG is loud.




Its like a portable MP3 player considering all the titles that have sound tests. :p
You know, except horrible sounding.

Intec PS2 LCD screen Mod

I found a controller at a junk shop for $5, and figured I would mod it onto a console. For the longest time I couldn't figure out how to add it to a console because I didn't know which cable was which. Now I figured it out: Orange: +12v (connects to a 7808 regulator so the voltage range should be greater and lesser than 12.) Black: Ground Brown: Ground Red: Right Audio input White: Left Audio input yellow: Composite video input Now I can finally build it into something. Maybe my new Sega Genesis 3, since it will fit right on the face of it and hopefully can share the same +10v power supply!

Jazz Disassemblies Ep3: Sega Genesis Saving Teardown

I love the Sega Genesis, but rarely do anything with it. I have made a handful of reproduction carts in the past because there is nothing better than playing games on real hardware but I always have a regret after destroying a donor cartridge, whether it is sports or not. One of the goals I always set myself up with during a creating is to use 100% renewable components. By renewable, I mean of course modern and commercially produced components; nothing salvaged and nothing obsolete. Having nothing obsolete is very difficult in my circle of interests, but salvaging components is my greatest downfall.

During my journeys into the technologies that Sega and other companies used within the cartridges for the Sega Genesis/MegaDrive, I have found three official forms of saving data. Two forms use serial EEPROMs and the third uses the tried-and-true parallel SRAM with battery backup. My goal is to recreate these cartridges using new components and my stretch goal is to expand the addressable memory or just to improve them in some way while making the carts themselves renewable.

We already know that the plastic shells can be remade by the everyday hobbyist and their 3D printers and circuit boards can be fabricated by Chinese companies for pennies on the dollar. All that leave now is the components which are definitely on their way out of style. The components that we are looking for are 8- and 16-bit, parallel ROMs and RAMs. Referring to a statement above: by renewable I meant purchasable from Mouser or Digikey, etc in large quantities which will later be restored. Glancing at Mouser (My supplier of choice) I have already been able to locate a handful of ROMs and RAMs that come in both selectable 8- and 16-bit configurations!

The next goal I will have is to recreate the higher density logic with PLDs, but that is best left for another time.

1. KM62256 Parallel SRAM

These boards found in most of the miserable football and soccer games. Until I find another varient, I will cover one such board revision: "171-6279A"

The board seems to be made by Sega though I have long lost the ROM which was originally soldered in. It contains:

1x (CE) 47uF electrolytic capacitor
5x (C1-C5) .1uF ceramic capacitors
1x (BAT) CR2032 coin-cell battery
1x (IC1) 42-pin Mask ROM (27c160 equivalent) - 16Mbit
1x (IC2) KM62256BPL-7L, 32Kx8 bit (32Kbyte) Low Power CMOS Static RAM
1x (IC3) BA6162, Reset IC with battery backup function by Rohm
2x (IC4, IC5) 74HC00AP, Quad two-input NAND gate

I have already recreated everything on the board in Eagle PCB libraries including the board dimensions and general component layout. Tracing all of the connections is slower work and I will get to that eventually. In the meantime, my goal is to layout a functionally-identical board with 3v3 ROM/RAM, SMT caps and level shifters for proper data flow. THen we will have ourselves a flash cartridge!









Above you have seen the board itself with and without components. Ignore the text on the Mask ROM though since I just stuck a random IC in there to show it with one.

Looks pretty good if I do say so myself, though the traces are not as authentic as the layout. Sega never seemed to use top-side pads. They have vias which allow for double sided boards, but I have only seen EA cartridges that use top-side pads. These pads of course make for miserable desoldering since I need much more heat... and patience.

Some fun facts about this board is that the ROM is 16-bits but the SRAM is only 8-bit. Although I do not have the full details on how the software accesses these, the Gen/MD has two pins which are called !LDSW and !UDSW (Upper Data Set Write and Lower Data Set Write). When reading from RAM, the processor ignores the upper byte of data since there should be nothing there. While writing though, the !LDSW pin goes low which enables the !WE pin on our RAM. These two pins are for transferring 8-bits (one byte) at a time rather than 16 (two bytes).Not knowing how to activate either of these pins, it would seem that someone may add a second SRAM and use the currently unused !UDSW pin as the enable.




The above picture is how I found the glue logic for addressing our memories. Only 6 out of 8 gates are used which is a waste of space and battery power since the unused pins are connected to the Vout pin on our reset IC. If you think about it, the three NAND gates that have both inputs connected act as NOT gates which is something we would take into consideration if we were to redesign this with single-gate SMT ICs or on a PLD.

one problem I have with this board is that A21 and A22 are simply left hanging. Just a guess, but using A20 as a ROm address and A21 in the logic would expand the addressable memory, but Sega chose not to for some reason.

2. Acclaim Serial 24LC02B RAM

The next board I will cover is the P/N 670120 REV 2 by Acclaim. The contents of our board are as follow:

1x (C1) 47uF electrolytic capacitor
4x (C2-C5) 0.1uF ceramic capacitors
2x (R1, R2) 4.7K Ohm resistors
1x (U1) Mask ROM (capacity not yet known)
1x (U2) 74ALS138N, 1-of-8 decoder/demultiplexer
1x (U3) 74ALS74AN, Dual D-type flip-flop with set and reset
1x (U4) 74ALS125AN, Quad TRI-STATE Buffer
1x (U5) 24LC02B, I2C™ Serial EEPROM (2K capacity)

As you can see, the naming routines is different than that of Sega and yet again, we could reduce the chip count to much less with a PLD. U2-U4 could easily be designed in a PLD to reduce space and cost. For the time being, I assume the resistors are pull-ups or pull-downs.








3. Acclaim Serial 24LC04B RAM w/ LZ95A53

You're probably thinking that I recycled this board from a previous post and yes, yes I have. It does pertain to the topic though and I can probably shed a little more light on the special IC now that I know more about !LDSW and serial eeproms.

Anyhow, this board contains:

1x (C1) 47uF electrolytic capacitor
4x (C2-C5) 0.1uF ceramic capacitors
1x (R1) 10K Ohm resistor
2x (U1, U2) Mask ROMs (27c160 equivalents)
1x (U3) Acclaim LZ95A53 (memory mapper, glue logic, serial data interpreter, etc)
1x (U4) 24LC04B, I2C™ Serial EEPROM (4K capacity)

Above is the board that I created by probing all of the traces. Looks nice, but my next goal would be to reverse engineer the Acclaim's LZ95A53. Unfortunately, I have no scope to do so...



The above picture is my schematic which shows the connections on the LZ95A53. I had to make an addition to my cartridge connector since it uses several different pins that very few others use. I believe that the Acclaim's LZ95A53 IC contains the same logic as the board which used the 24lc02 serial RAM. Again, I cannot test this theory.




In hindsight, all of these boards used 27c160 equivalent Mask ROMs. The 27c160 can store a 2MB ROM which means the board with 2 Mask ROMs had a 4MB game. A piece of information for those making reproduction carts with the 27c400, 800, 160 and 322's, the first three mentioned all have a !BYTE pin. This pin allows for the EPROM to function as either an 8-bit or 16-bit ROM which means you may use it in many different systems.

Besides a little bit of work on the silkscreens, these boards are all ready to send to any fab house, granted they make 1.6mm thick boards. I will also be adding some more pictures of the other two boards shortly. Thanks for reading.

Acclaim Custom IC - Sega Genesis/MegaDrive

While viewing different game cartridge boards for the Sega Genesis, I came across a few Acclaim boards. I no longer can remember what games they were because I have long removed the Mask ROMs, but one board has three 74-series ICs and a 2k eeprom for saving purposes. The fact that they utilize both parallel and serial communication methods causes problems for me, but we will get to that later on. In any case, the second board contains the 20-pin "Acclaim LZ95A53" IC (datecode 9453 A). this board also contains a 24lc04, which is double the size of the 24lc02 on the other board.

While searching the custom chip, I found that there is little information on it. I can only come to the conclusion that it is a custom memory mapper AND parallel to serial data conversion IC.

The three ICs on the first board from Acclaim are the 74ALS138 decoder used on many many other boards for memory expansion, a 74ALS74 Dual D-type flip flop and a 74ALS125: Quad bus buffer with three states. I cannot prove this theory yet, but I believe the Acclaim LZ95A53 is all three of these ICs built into one. 20 pins could easily achieve this since many pins are shared and many others are not used at all on the other chips.

Here is the first circuit board with all four ICs. Four ceramic capacitors, one electrolytic and two resistors. The board originally had only one mask ROM so I assume it was a game of 2MBytes.





And here is the circuit board with only two ICs. The custom "Acclaim LZ95A53" can be seen at the top right. By reducing the three chips into one, they also reduced the required space on the board, reduced component count and most likely cost. They also switched from their own board to a board made by Liteon. There are several improvements that I can see on the board when they made the switch. Not only is the copper much more smooth but the solder mask is shiner and they even tented the vias. I rarely see tented vias on game boards. The drills are also smaller and less sharp. The previous board has splintering around all of the drills.





Looking at the revision designators on the boards, the liteon is newer. One more thing that I noticed about both boards is that neither have break marks to show that they were panelized. Acclaim chose to finish off the sides very nicely which is odd. Game boards were technically not supposed to be seen by the end user, but they took the extra time and effort to clean them up as opposed to (looks over at other boards on desk) konami and Capcom. A third Acclaim board that I own which is yet older than the two in detail above has also been finished on all four sides.

In conclusion, Acclaim seemed to have cared a little more about the games that they produced. Going the extra mile to make their boards of higher quality and to develop proprietary ICs. I can respect them for this though I never had any doubt about them. EA on the other hand...made boards that I despise. I may post about them another time. For now I will be following the pins on the LZ95A53 back to their origins and proving whether or not it is simply a combination of three 74-series ICs. Granted it is, I will have a pinout shortly there after.

EDIT:

I have since begun following pins on the board from the custom chip to other locations. So far it would seem that I was correct, mostly. The chip is definitely decoding ROM address and possibly RAM addresses (granted your board requires parallel RAM) and has connections with the Serial RAM; however, it is also making connections to the !AS pin on the 68000 and the !LDSW and !UDSW pins. these pins are beyond me, but I have read they have to do with writing only a single byte at once rather than the full 2-bytes (16-bits) that it capable of.

I will continue to edit the diagram below once I have more information:

          __  __                  
A20    1=|      |=20   VCC     
A21    2=|      |=19   NC 
/C_OE  3=|      |=18   !OE2(ROM2)     
/C_CE  4=|      |=17   !OE1(ROM1)     
/AS    5=|      |=16   NC
D0     6=|      |=15   NC     
/RES   7=|      |=14   NC     
/LDSW  8=|      |=13   NC

/UDSW  9=|      |=12   SDA(24lc04)
GND   10=|      |=11   SCL(24lc04)

         |______|

Also note that pin 12 which connects to SDA of the serial eeprom is also connected to VCC via a 10K ohm resistor. I assume this is a pull-up resistor for data