Thursday, December 12, 2013

My DIY Modular Euro Rack for $10

Assuming that you have screws, a simple drill and a small hand saw, you can expect to spend $10 on a two-row, 12" wide Euro Rack. Yes, it is all wood and yes, you will need to drill new holes for each new module that you purchase or build but for 10 bucks, who's complaining?


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Its pretty simple, but what can I say? Im broke. :P


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My plans are to use this for testing purposes even when I do find the time and money to build a real quality rack with metal parts. In any case to build your own, head down to menards any pick up these items:

2 each:

3/8 X 36 Poplar Square

$0.89

1 each:

5/8 X 36 Poplar Square

$1.99

2 each:

3mm X 4" X 12" Craft Plywood

$0.99

2 each:

6mm X 6" X 12" Craft Plywood

$1.99

There will be different taxes depending on your location so I did not include that in my total. Michigan has a small 6% sales tax, so I am lucky. I forgot to take photos while I was working, so I will draw up a diagram shortly. It is not terribly complex, so you should be able to figure it out in the meantime. 

I did also buy another piece of wood to make faceplate out of. Knowing that the euro modular faceplate should be 5.25" tall, I bought a 3mm x 6" x 12" panel and will cut it to size when need be. I used this for my power control faceplate which has a switch, two LEDs and an audio input. Again, this box is probably going to be used for testing rather than audio production. The LEDs correspond to + and - 12v which I will install once I purchase a regulator. The power control plate is 10mm wide, or 2HP. 

Here is that panel if you are interested:
I want this to run on AC, but a regulator board that I am interested in accepts 14 - 24v DC as a source so I will end up building a wall wart into the box as well. You can see that I added a speaker from an old noise making toy. I was lucky enough to have found one with a holder rather than one that was just glued in.

As soon as I power it up, I will post another update. 

Cheers all,
Jordan

Thursday, November 14, 2013

Jazz-Assembly #2 - Yup, Another ArduinoBoy

Everyone and their mother has made one, so what took me so long? I have built them before, but this time I designed a PCB. What differs between mine and anyone else's is that I used economical parts rather than a pre built Arduino or an Atmega pulled form one with a bootloader.


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The entire board is a tiny 5cm x 5cm, MIDI connectors and LEDs included. I also plan on designing an acrylic shell to sell along side them, though anyone may choose to house it in their own enclosure.

Anyhow, this was the first time I had used SMT components besides an IC. Passive components including the resistors and caps were a new item for me to tackle. They did not challenge me as I had hoped. At one point, I blew one away from the pads, but it was all too easy to fix.

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Below is a shot for size comparison. You may have noticed in one of the photos that there is a notch on one side with a hole about 2 millimeters from it. This will be used for a zip tie so that I can ensure the cable does not break free. I will upload another picture once I complete that portion.

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Below is the wiring that I used to program both the flash and fuse bits. It is the same Bit Bang connection as we used on my version of the Gameboy Programmer board in a previous post. I found that the fuse bits were the most difficult to figure out in the whole project. in the end, I decided just to copy the fuse bits from a Pro Mini 5v/16MHz because that is what configuration I went with here.

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Thanks for reading. All credits for the ArduinoBoy go to Trash80 (Timothy Lamb) as can be found here:
https://code.google.com/p/arduinoboy/

Monday, October 28, 2013

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.

Friday, October 11, 2013

List of things I will order again from Mouser



Maybe its a silly blog post, but it may help someone. Here I will post and frequently update items that I ordered from Mouser and liked so much that I would or will order from them again. I will try to follow the layout of:

Name - info w/link
Cost
Why I liked it
My picture - if available

Mouser has millions of items and more than half of which have no pictures. Some of these don't even have that great of datasheets to read through, so ordering parts can become exhausting and stressful.

Once this list becomes larger, go ahead and hit Ctrl + F to search for an item you might need; for example, an ISP, USB or MIDI connector, the common 104 ceramic cap or whatever else. The things I look for in an item are cost and usefulness. I need a cheap item that works for me without begin crap.


0.1uF leaded Ceramic Capacitor
$0.10 x 1, $0.08 x 100
2.54 mm lead spacing takes up minimal room but is easy to solder by hand.
View

USB Connector female TYPE B in Black w/rear shield
$0.63 x 1, $0.53 x 10
Cheapest I could find and has angled legs to hold itself in place prior to soldering.
View

3mm Red LED
$0.07 x 1
Simple 3mm diameter, rests flat on your board.
View

3mm Green LED
$0.08 x 1
Simple 3mm diameter, drawback: legs flair out so it does not rest flat on your board.
View

Elusive 3-row, 26-pin D-sub connector
$1.53 x 1
Super cheap considering the regular going price. Fits Macintosh LC Apple IIe card.
View

Hood to fit 26-pin connector
$0.46 x 1
Fits 2-row/15-pin connector and 3-row/26-pin connector
View

Atmega8515 TQFP-44
$2.66 x 1, $2.54 x 10
Cheapest option and easy to solder package, small size
View

Solder Flux Pen
$4.78 x 1
Coolest, best, cheapest felt tip pen with soldering flux inside! It lasts and lasts.
View

Gameboy MBC - Which to choose?

Just a quick overview for unfamiliar readers before we get into the thick of it.

The Nintendo Gameboy uses a Memory Bank Controller inside of official cartridges for switching between banks of memory and ultimately expanding the addressable memory. The MBC will switch between banks of both ROM and RAM so that the programmer may code larger games and backup more data in save files.

There are four main MBC's numbered 1 through 5 and excluding 4. The reason I am writing this is because each following revision did not simply add more addressable memory. Each one has unique capabilities built in as well as expanding the addressable memory. in general the MBC's function by waiting for specific data bits to be written to yet more specific memory locations. Once the data in question is written to the specific memory location, the MBC switches the active bank of ROM and RAM to accommodate more code.
I will summarize each MBC as well as quote some information from datasheets.

MBC1


Is the first in the series of controllers which did only expand the addressable memory. Since the gameboy has 16 address pins and 8 data pins running through to the cartridge, the gameboy may without an MBC address only read from and write to a maximum of 256Kbits or 32Kbytes which is incredibly small considering Mario Land has 12 massive levels with multiple means of gameplay including the platformer and shooter, in both an airplane and submarine. Some of these levels even have secondary underworlds where Mario drops to an extra map off screen to collect secret coins or other items.

In any case, the MBC1 has two different modes to choose from. There is the 16Mbit ROM/8KByte RAM and 4Mbit ROM/32KByte RAM. 

Note: RAM is an external IC which needs to be connected to a battery while disconnected from gameboy power to retain data.

MBC2

Similarly to the MBC1, the MBC2 maps extra banks of memory with specific memory writes; however, it may only map up to 2Mbits or 256Kbytes of ROM. Why a decrease? Well the magical thing about the MBC2 is that it contains 512 x 4 bits of SRAM built into the IC itself. This saves a lot of room on your cartridge board granted you are designing one.

The MBC2 can save money on RAM and space on your board if you are programming a small game that requires little ROM and RAM. Referring to the MBC1 above, if you wanted to offer a saving feature, you would need to source a RAM IC as well and route all of the Address, data and control pins to another location on the board.

MBC3

The MBC3 may again address up to 16Mbits of memory, but has a major feature built like the MBC2 has RAM. The MBC3 has an RTC or Real Time Clock built in. The RTC while still needing battery power when disconnected, offers a real-time count so that games such as pokemon may tell whether it is night or day, or when an hour in real life has passed for example.

Some games use the MBC3 without utilizing the RTC, but games that do include Pokemon of Generation 2 and Harvest Moon.

MBC5

Lastly, the MBC5 is the final Memory Bank Controller from Nintendo. This particular MBC does not come with internal RAM or an RTC. It simply maps huge amounts of memory. It may map up to 64Mbits of ROM and up to 1Mbit of RAM but not both. There are different configurations to choose from; these are just the maximums.

This MBC which I find in nearly every Gameboy Color cartridge regardless of ROM size is guaranteed to work with the GBC's double speed mode. The others seem to work just fine too though, considering any GB game will run on your GBC.

For more information on how to use the MBC's with software, please refer to "Cartridge Types" in this document:
http://www.devrs.com/gb/files/gbspec.txt

MBC CPLD Clones & Reproductions

Aside from the Official Nintendo MBC's, people have had major success in recreating them using CPLD's. Both Homebrew developers and Chinese pirating companies that is.

Since the MBC2 and MBC3 contain separate ICs, recreating them is much too difficult for a single person. MBC1 and MBC5 on the other hand can and have been redesigned by using CPLD's. They way they work as mentioned above is that they look for specific data bytes to be written to specific address locations. This Logic can be entirely drawn out using logic gates, which in turn can be programmed onto the CPLD.

MBC1 - CPLD

The MBC1 being the most simple, can be drawn using as little as 11 gates! (granted you do not need RAM)
















MBC5 - CPLD

The MBC5 is much more complex of course, but it has also been cloned successfully by at least two separate people using two different CPLD's. One person used the XC9536 and the other person used the XC9572.

XC9536
http://chipmusic.org/forums/topic/2988/mbc5-clone-in-cpld/
and XC9572
http://home1.stofanet.dk/hvaba/gameboy/mbc5cpld/cpldcart.html

Depending on the number of inputs and outputs, more complex logic ought to be designed using PLD's or CPLD's. Not only can you save money on IC's, but space on your circuit boards. More often than not, a logic IC will take up space on your board and have a handful of unused pins and gates which is wasteful and lazy.

As always, thanks for reading! I hope I opened someone's eyes to new and old hardware.
Cheers

Wednesday, September 25, 2013

Using the Gameboy Programmer Board

Granted you have either bought a complete board from me or followed my DIY setup guide to a 'T', you are ready to use your Programmer/Reader board.

You'll need the software for the PC-side communication. You can find it on the author's site here:
http://www.reinerziegler.de/readplus.htm#Home made programming systems

Click the link "GB Cart Flasher programming software V1.1" and download the files. Install it where ever you like. If you are using Windows 7, you may need to run it in compatibility mode for Windows XP. I do and it works. If you don't know how to do that, right click on the shortcut and click properties, then check the box for compat mode and choose Windows XP. Then hit OK.

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Ready!

READING DATA

Plug in your device and then start the program. I like to make the window larger because there is a readout of what is happening. The readout should state that the program has started, whether it finds the device and then what firmware version is running on the device.


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Plug in a cartridge and hit "Cart info" to make sure that the cart has a proper connection. If everything is unknown and there is no "--ROM/FLASH content information" then remove your cart, clean the contacts and try it again.

Eventually, you should get a good connection and it will look something like this:


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take this info and set the boxes on the left to reflect it. In this case, we can see that the ROM is 512KBs, the RAM is 8KBs and the MBC is MBC1. It may not be necessary, but I will change the MBC to MBC1 rather than Auto just to be safe. Set those boxes, hit "Read Flash" and designate a save location.

The progress bar starts moving and the readout states that it is reading. After a time depending on the ROM size, you'll see ">Success!" Follow the same method to backup your save files but hit "Read RAM" instead.

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As you can see above, I backed up both files. Save files are not compatible with all emulators, but they are good to keep on hand since the internal batteries are dropping like flies now-a-days.


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WRITING

The method to write ROMs and RAMs is the same, but just with two different buttons.
Plug in your "flashable" cartridge and click on "Cart Info" again. You'll either be given the contents as before or you'll be given the "Cartridge is blank, damaged or not connected" message. Hopefully, it is just blank. ;)


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In any case, hit "Erase FLASH" and wait for the process to complete, otherwise you will get a timeout error if the ROM is already full.


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Once it succeeds, press "Write FLASH" and browse for your ROM. It will go through the process and complete.


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Thanks for reading and Enjoy your gameboy!
~Jazz

Sunday, September 22, 2013

Populating the GB-Programmer (Jazz-Assembly #1)

The board has been designed to accommodate different methods of programming the Atmega8515 (hereby simply called 8515). Once programmed, you may never choose to reprogram it again because there may never be updates to the firmware anytime in the future.

Step 0.
Admire your beautiful new toy. 

It shall prove to be very useful regardless of your individual purposes. Also, at no time should you power your board until I say so.

Step 1.
Soldering both SMT ICs

The picture below is of two board prior to me cutting them apart. To reduce cost, I panelized my design.


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You may choose to solder one IC at a time or both at once depending on your skill and resources. It would be highly suggested to use either a hot air gun or some type of oven and solder paste. Soldering by iron is perfectly possible, but creates more chance for failure. If you are a frequent reader, you should know that I now own an awesome hot air station, so I also bought a tube of solder paste.

Simply apply a very small amount of solder paste to the bare pads and carefully place your IC over top of them. Make sure that it is aligned as closely as possible, not forgetting to orient pin 1 in the right direction. Pin 1 is designated by the white circle on the board.

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Once you finish both ICs, make sure that there are no shorts in places that they may not be. If you find one, attempt to draw the solder off of the pins with your iron or solder wick. Check it again and once satisfied, move on.

Step 2.
Through-hole components.

As much as I had hoped not to use any through-hole components, my audience insisted. The through-hole components required include:

2x 0.1uF ceramic capacitors (may be labelled 104)
1x 4.7uF electrolytic capacitor
1x 10K ohm resistor
1x 1K ohm resistor
2x 220 ohm resistors
2x LEDs (two colors)
1x female USB type B connector
1x gameboy cartridge connector

For the time being, do not populate C4, R6 and R7. These are not relevant at this time. You may choose to use a 6MHz ceramic oscillator, but I suggest saving the money and moving on. If you do though, cut the trace leading from it to the FDTI chip.

Start by placing the leads into the holes and bending them away from center so that they stay in place. Sodler each component on the underside and clip the legs at the board. Some people would suggest to clip them before soldering though.

Also make sure that the electrolytic capacitor (C3) faces negative lead down as shown below. Each components has the appropriate value marked on the board, so you cannot go wrong. Seating the gameboy cartridge connector may be the most difficult through-hole component. It has the most pins and each of these pins could be slightly bent from originally removing it. Take your time and do not stress.

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The LEDs can be any color you like, but know that the one farthest from the resistor is power and the other one is activity. I prefer my toys to have a green power LEd. ;)

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Step 3. 
PC Connection

Check your SMT soldering ONE MORE TIME. If and only if there are no shorts between pins, connect the board to your PC and cross your fingers... IF all is well, the LED should light up and a driver should automatically install for your device. It will also be given a COM port number.


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Step 4.
Programming the FT232RL and 8515

Thats right, you're going to program both ICs. There is only one modification that needs to be made to the FT232RL (hereby simply called 232) which is to make it output a 6 MHz clock rate. This is for the 8515 to run on.

First, the 232's internal eeprom must be modified. To do this, we will use FT_Prog found on the FTDI website here:
http://www.ftdichip.com/Support/Utilities.htm#FT_Prog

Only one modification must be made and that is to change the CBUS0 pin to act as a 6 MHz clock. We will not worry about the other pins because they are all unconnected. CBUS0 is one of five programmable I/O pins and there are many options to choose from, but I am not going to cover these here.

Install FT_Prog and run it. You'll be greeted by a well designed GUI ... just don't touch anything. plug in your device and it should install a driver if it has not already. Once "Your device is ready to use" go ahead and click "Scan and Parse" which looks like a magnifying glass. Your device should pop up in the dialog box under device tree like this:

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You can see that your device is already programmed, but we must now change one function. Expand the device tree as such:
FT EEPROM -> Device Specific -> IO Controls -> C0
Use the drop-down to select CLK6 in the C0 bus only. The other pins are all useless as they are not connected to anything. Ignore them.

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Click on the lightning bolt which is the program button, make sure your device is selected and press "program" if and only if you are positive you did not change any other settings.
The bottom of the window will say finished and then ready. Close the window and close FT_Prog, then disconnect your programmer.

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Reconnect your device once more and it should install the drivers again and give it a new COM port. You can now move on, but if you were to open your device in FT_Prog again, you would notice that C0 is still set to CLK6. Good job!

Just a note, but the reason you should not touch any other options in the eeprom settings is because there are too many settings that can be set incorrectly. For example, if you were to program your device to use an external oscillator, it would be rendered useless and you spent a lot of time and energy soldering that chip perfectly! So be careful!

Step 5.
Programming the 8515.

The easiest way to program the 8515 is via FTDI BitBang. It is a totally new concept to me, but incredibly useful considering how much people want to charge for ordinary ICSP programming kits. It may be a tad bit slower at programming, but since you will only program the 8515 once, it does not matter.

I put together a file-pack to get you started. This pack  includes AVR_DUDE, my custom config file special for this programmer and the hex file which needs programmed to your 8515. I am writing the guide on the GUI version of AVR-DUDE. Everything is easier with a GUI, though you have to show a little love for the tried and true command prompt. ;)

Download it here:
http://www.noisechannel.org/wp-content/uploads/2013/09/GB-Progger-kit.zip

Lets get started.

Go ahead and hook up your programmer if it is not already. Open avrdude-GUI.exe.
1. Direct the first box to your avrdude.exe
In our case, we will be using the avrdude-serjtag that you downloaded.
2. Pull down the "Programmer" Box and select the "FT232R Synchronous BitBang for Jazz (GBProgger)."
3. Leave the port drop box blank.
4. Locate "ATmega8515 (m8515)" under the "Device" drop-down.
5. Type "-P ft0 -B 4800" in the "Command line Option" box. It should look just like this below:


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6. Click the "Read" button under Fuse. This will show you the fuse bits on your 8515 which must be changed. It does not matter what they are now.


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7. Change the fuse bits to C910 as pictured and hit write. It will be very fast and just ask you if it went well.


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8. Now erase "-B 4800" from the "Command line Option" and browse for the hex file under Flash then hit write. It is also fast, too fast for me to get a screenshot even.


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9. Exit and done. Disconnect your device and reconnect it. If all went as planned, you now own a GB Programmer and Dumper for whatever needs you may have.

Lets test it out, shall we? That is another blog post, for another time. See you then! :D

 Cheers,
Jazz

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.

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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.

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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