Hello there!
Glad to have found this forum, where there are so many well-known retrogaming hardware experts around! Having some SNES software and hardware experience myself (translation, ASM, console & cart modding), this is the place I've been looking for.
Well, let's head on to business. I recently ventured building a 32 Mbit SNES cart using one 16 bit 27C322 EPROM. I used
Siudym's untested schematics.
Here's what the completed thing looks like:
I know it's butt-ugly, but hey, it's my very first beta HiROM 27C322 SNES cartridge.
And unfortunately, it does
not work. All I get is a black screen once that baby is powered up.
I tried to e-mail Siudym for a solution, but he didn't reply. Then I asked d4s for help - thanks again, dude! - but to no avail. Even with his suggestions, I wasn't able to get this thing to work.
Here's what I've tried so far:
- the original schematics (Siudym)
- connecting the SNES bus's A0 to pin 2 of the 139 and A1-A21 to A0-A20 of the EPROM respectively in order to avoid having to byte-swap the ROM in any way (d4s)
- not making the EPROM & SNES /OE connection (d4s)
- using HC microchips instead of LS ones to make sure the ROM data gets on to the SNES bus fast enough (d4s)
Nothing works. I even tested it on d4s' Ultra16, which has a memory viewer. The banks C0-FF (which should contain the ROM data since it is a HiROM game) remain empty, just like when no cartridge is inserted at all. Also, I checked the voltages on the 139, the two 245s and on the EPROM itself to make sure I didn't forget to make all the power connections. All VCC pins are at +5V as they should, and VSS is at GND.
Now, does perhaps someone of this forum have any idea what could be wrong? Any help would be greatly appreciated as I really want to finally get this project to work.
Thanks in advance!
orwannon
N.B.Please don't bother suggesting alternatives like using 27C801 EPROMs (I have successfully built carts using these), a copier (I indeed own one), or a Tototek flashcart (I'm going to buy one anyway). In this thread, let's just talk about connecting 16 bit EPROMs to the SNES bus. Savvy? 
Hmm. I don't get why that schematic is using a bus transceiver. I thought for a few minuets and came up with this: (sorry for the crude MSPaint)
This circuit replaces the transceivers in the design you are using with 3 state transparent octal latches (74xx373). In this schematic the 373s have their latch inputs tied high (transparent mode). The OE/ of the 373s are connected to the nand gates (1 74xx00 quad 2 input nand gate) which decode the upper/lower byte from the A0 and CE/ lines. I can't see why this wouldn't work but it is wholly untested. ^_^
Why use a latch for just the output buffers? I don't think it's wise to ignore the /RD signal anyway. If that were OK, you could then just use two 74257 3-state multiplexers and drop a chip. 257s are also cheaper than 373s and come in a 16 pin package instead of 20.
Edit: note typo that the 27322 doesn't have a A21.. so wire SNES A1-21 to 27322 A0-20.
If you're using 74HC parts, I'd probably ground the ROM's /CE to not float the inputs though this will consume more power.
The 74257s are definitely a better choice. I used a pair of them in my pcb design a while back. I'm not too sure about ORing /ROMSEL and /RD since SRAM /OE is connected to /ROMSEL. There might be some bus conflicts.
P.S. Thanks kyuusaku. I finished the proof of concept for the 96mbit game (95 mbit technically) with a working prototype. I didn't quite use your design but it put me in the right direction.
In the case of SRAM, yeah just use the SRAM decoder's output instead of /ROMSEL, but SRAM /OE shouldn't be connected to /ROMSEL at all though, just to /RD.
It's cool you made a 96M cart, what's on it?
Neviksti's version of Star Ocean.
Good catch on the typo. I meant to say that /RD is connected to SRAM /OE.
Ah! Much cooler than a test program, how did you decode SRAM? I've wondered if the SRAM area in that circuit I posted was suitable since I think it encompasses the standard HiROM area.
Wow, thank you all for your suggestions and new schematics!
shadowkn55 wrote:
There might be some bus conflicts.
So, do you mean /ROMSEL should be connected to the EPROM's /CE directly (and only), and /RD to the 257s' /OE only (while leaving the EPROM's /OE pin at GND as shown on kyuusaku's design)? Also, when using HC parts and thus grounding the EPROM's /CE pin, should I leave /ROMSEL unconnected? (/ROMSEL = SNES's /CE, right?)
BTW, as the SRAM on my PCB got erased during the tests, I presume an SRAM conflict in Siudym's schematics could be the reason for the ROM data not coming through ... This is just an assumption though.
Anyway, thanks for your help! I might put kyuusaku's design to the test shortly.
If anybody else should know how to get this done with transceivers as shown on Siudym's schematics, I'd appreciate it (especially because I won't need to buy new parts!
). His design can't be too wrong because the 16 bit adapter for the Willem EPROM programmer uses two 245s as well ...
orwannon
orwannon wrote:
So, do you mean /ROMSEL should be connected to the EPROM's /CE directly (and only), and /RD to the 257s' /OE only (while leaving the EPROM's /OE pin at GND as shown on kyuusaku's design)?
Noooooo, that would CAUSE conflicts as /RD (and thus 257 /OE) would be asserted on every instruction. You need it so only when both /CE and /OE are asserted the buffers output. If you only decode with /CE, then if a game writes to ROM there will be a conflict, /RD OR /CE protects against this.
orwannon wrote:
BTW, as the SRAM on my PCB got erased during the tests, I presume an SRAM conflict in Siudym's schematics could be the reason for the ROM data not coming through ... This is just an assumption though.
Just like my diagram, Siudym's doesn't account for SRAM. This has nothing to do with the design, just how you are not using the proper ROM select from the on board decoder (74139 or MAD-1 etc).
orwannon wrote:
If anybody else should know how to get this done with transceivers as shown on Siudym's schematics, I'd appreciate it (especially because I won't need to buy new parts! :P). His design can't be too wrong because the 16 bit adapter for the Willem EPROM programmer uses two 245s as well ...
Using 245s will "work" but it's not the most elegant way due to logical/electrical glitches. Unrelated but this is NOT a good way of bidirectionally accessing 16-bit memory, the only reason the Willem gets away with it with only two 245 is because EPROM can be programmed as small as a bit at a time due to their construction, this would not work for other 16-bit memories that need a complete word latched.
This is how you would build a working 245 version though:
Siudym's conflicts for the same reason I outlined above, mine WILL work as the 139 also implements /CE OR /RD.
And work it does! You rock, kyuusaku! 
As your version is not very different from Siudym's design, I just had to alter the /CE and /OE connections accordingly. For the record, I tied pin 1 of the 139 to pin 4 of the MAD-1. Works like a charm!
Thanks a lot!
I feel like trying out your "more elegant" design with two 257s next. I guess that when there's SRAM on the cart, I should use the on-board decoder's ROM select instead of /ROMSEL for one of the OR gate's inputs, just like I did now, correct? One last question on this would be whether you'd recommend any microchip type concerning the OR gate? Looking at the 139's
datasheet because you mentioned its OR implementation, I guess I could simply use that one (e.g. pins 1 and 3 as the inputs and pin 4 as the output) ...?
Anyway, big thanks again for your efforts and great technical help! I couldn't have done it without you!
orwannon
Glad you got it working! Now you can try tying the 27322's /CE to the /CE connected to the 139 (the MAD-1 output), this will give you better power efficiency ;)
orwannon wrote:
I feel like trying out your "more elegant" design with two 257s next.
To do that you can still use a 139 to enable the outputs, you just don't want to decode the enable signals with A0, only with /CE and /RD.
orwannon wrote:
I guess that when there's SRAM on the cart, I should use the on-board decoder's ROM select instead of /ROMSEL for one of the OR gate's inputs, just like I did now, correct?
You should always use the on-board decoder's ROM select, it's no different now with a 16-bit ROM than it was with an 8-bit ROM, the ROM must be enabled when the SRAM decoder wishes.
orwannon wrote:
One last question on this would be whether you'd recommend any microchip type concerning the OR gate?
7432 are the typical OR gate IC, but I wouldn't use a discrete chip for only one logic gate... Since you aren't building boards I guess it doesn't matter much but I'd try to integrate the logic into the ROM/SRAM decoder. 74139 are typically more useful to keep around than 7432.
orwannon wrote:
Looking at the 139's
datasheet because you mentioned its OR implementation, I guess I could simply use that one (e.g. pins 1 and 3 as the inputs and pin 4 as the output) ...?
The 139 is a decoder, it doesn't really have an OR function, I just chose the outputs which gave an OR condition, and further decoded that with A0 to chose which buffer to enable/two birds with one stone.
Programmed and verified a 27c322. Re-read it with friend's TOP2004 at his setup, and then played the rom on bSnes emulator. Worked perfect.
I do not have 257s and ordered them from Australia (best price, highest amount lol). That is estimated at 5 weeks SeaMail *seller said no AirMail to Canada? Wtf... anywho back on track.
I have an LS139, 2 LS245s, and a programmed 27c322.
http://nintendoallstars.w.interia.pl/ro ... c322_8.png
The only changes I would need to make to siudyM's (link above) instructions are to ground the 3rd pin of the 139 (Kevtris), and ground the 27c322's E (CE) and GVpp (OE). I ran it up, multimetered and checked the wiring. No shorts for sure (checked 3 times) and it did not work.
HELP
edit: tried removing the ground from leg 3 of the 139, did not work
Draw a *complete* diagram of how the cart is wired and I'll correct it.
Permission to rage at my stupidity is granted
. This is maybe too difficult a hobby to have taken up
.
edit: grounds and vcc are all connected correctly too, I check with a multimeter
edit2: "As your version is not very different from Siudym's design, I just had to alter the /CE and /OE connections accordingly. For the record, I tied pin 1 of the 139 to pin 4 of the MAD-1. Works like a charm! Smile Thanks a lot! " - orwannon
Take a look at kyuusaku's diagram:
kyuusaku wrote:
See, you wire SNES A0 to pin 2 of the 139 and then
SNES A1 to EPROM A0
SNES A2 to EPROM A1
...
SNES A20 to EPROM A19
SNES A21 to EPROM A20
and leave SNES A22 unconnected.
Don't ground the 139's pin 3, but instead wire that to pin 24 of the MASK ROM (note that you have to use a PCB with a 36-pin MASK ROM - not only for correct pin numbering). And pin 1 of the 139 should be wired to pin 4 of the MAD-1 (if applicable) or to MASK ROM pin 33.
This works great for me. BTW, kyuusaku's "257 version" works just as well - and is a bit easier to construct.
Pin 33 - /OE
Pin 24 - /CE
Is /OE the same as /RD?
So in the diagram, do I have the /CE and /OE connections on the LS139 mixed up?
/OE does not go directly to the 245, it goes to the 139. Both of the 245's pin 1 should be grounded--very important!
If you're using something other than a 74LS139, you should tie 139 pins 13,14,15 to +5V as well.
Lastly ROM /CE should be taken from the mask ROM /CE pin hole, because that pin's function never changes, the MAD-1 pins do depending on the board.
If your 245 chips are 74LS, you can tie the EPROM's /CE to 139 pin 1 as well to save a little power.
Also, I did it right down to the last spec with multimeter checked, no shorts or anything and programmed the chip correctly guaranteed. No go, orwannon if you ever read this, since you tested it. Can you check the above schematic and
"For the record, I tied pin 1 of the 139 to pin 4 of the MAD-1. Works like a charm!"
There is no way that can be right... Pin 1 is /CE the MAD-1 Pin 4 links to /OE on HiRom Carts and is not used on LoRom Carts ( I mean the pin 4, not the mad-1 in total ). I even checked with a multimeter, pin 33 on the maskrom (/OE) leads to Mad-1 Pin 4.
Could it be that you confuse SNES /OE with /CE? There are many docs out there on the net in which these two are mixed up.
Your "corrected" schematic is horribly confusing. Go with the schematic kyuusaku posted (and I quoted) earlier. That'll work.
I did it orwannon, I even tried to reverse the OE and CE did not work... how did u reply so fast lol? who r u on IRC? lol
edit: my left 3 diagrams of the ICs are the exact same as kyuusaku's. But I did ground and add the +5 connections to the legs not listed (10 is a ground and 20 is a +5V on the 245, and 8 is a gnd while 16 is a +5V on the 139).
Is that correct?
Pin 1 of the 139 is connected to the /CE of the maskrom pin 24, and pin 3 is connected to the /OE (pin 33 of the maskrom).
If both of that is right, I will try editing my VCC and ground such that they all come from seperate wires, because right now, its 1 to the 139, and then they branch out from there for gnd and vcc.
I dunno, maybe you have the ROM's endianness backwards, thankfully you can just swap 139 pins 4 and 5.
Oh, what is A0 on the ROM connected to? Sounds like you have those mixed up. ROM A0 should connect to SNES A1, ROM A1 to SNES A2 etc.
kyuusaku wrote:
I dunno, maybe you have the ROM's endianness backwards, thankfully you can just swap 139 pins 4 and 5.
Oh, what is A0 on the ROM connected to? Sounds like you have those mixed up. ROM A0 should connect to SNES A1, ROM A1 to SNES A2 etc.
I checked that, it is wired correctly 100%. I have everything wired as per the diagram I posted above, if that is correct, then my problem lies with my rom or ICs.
Edit: ONE MORE QUESTION
If you have thick enough wire it shouldn't matter.
kyuusaku wrote:
If you have thick enough wire it shouldn't matter.
I was using 30AWG, but I have some 22AWG wire. Should I stick to the 30, or move the gnd and +5v to 22AWG wires?
30 AWG isn't very good for power, you're limited to about 100mA per tap which I guess could be exceeded. I kind of doubt that's the problem though, more likely it's something logical. Did you try swapping endianness?
kyuusaku wrote:
30 AWG isn't very good for power, you're limited to about 100mA per tap which I guess could be exceeded. I kind of doubt that's the problem though, more likely it's something logical. Did you try swapping endianness?
I just took the 27c322 out and re-read it... for some reason one of the hex's was wrong.. I had tape on the window by the way.
Willems programmers are a piece of crap lol. 25 degrees celsius, 12.0V VPP, 6.2V VCC +/- 0.25V (I get 0.64 V). Right off the datasheet and these specifications will not work for me with correct jumper settings
... grrr
I'm not surprised. The older Willems with Jumpers/dip switches and such are crap. MCUMall sells newer USB (no jumpers) programmers and they have 16bit adapters for chips like 27c322. Ofcourse they are more expensive than the average junk willem clone that is parallel port with jumpers and dip switches.
lunaris wrote:
I just took the 27c322 out and re-read it... for some reason one of the hex's was wrong.. I had tape on the window by the way.
...But did you swap endianness? The programming software might have chosen little-endian, which would mean you'd have to switch the buffer enables.
kyuusaku wrote:
lunaris wrote:
I just took the 27c322 out and re-read it... for some reason one of the hex's was wrong.. I had tape on the window by the way.
...But did you swap endianness? The programming software might have chosen little-endian, which would mean you'd have to switch the buffer enables.
no sir, i use the willem software, all i do is select 27c322 and change the jumper settings to what it is listed as + 6.2vcc (@6.4v irl) + 12.0V VPP
what is endian-ness and how would i? is there another common term for it as I have never come across that word?
Quote:
what is endian-ness and how would i?
Let me Google that for you.
The ROM is 16-bit wide but file data is addressed sequentially in 8-bit bytes, so the "endianness" determines which byte is placed in the upper and lower 8-bits of the 16-bit word. The circuit is configured for big-endian data (even bytes are D15-8), but there's a good chance the Willem software chose little-endian. But if this is the case, you don't need to reburn the ROM (normally you would), you just need to exchange 139 pins 4 and 5 which in effect swaps bytes.
tepples wrote:
Quote:
what is endian-ness and how would i?
Let me Google that for you.
Thanks
What my test cart looks like:
Using SN74LS139AN + (2x)SN74LS245AN + a Zif Socket for 27c322 and a HiRom cart with SRAM and MAD-1.
Extra WIIIIIDE picture
Also, if I want to make a 48mbit game like Tales of Phantasia English Patched... I would need 2 16-bit eproms for the task.. Is it even possible to link up 2 27c322 to 1 snes bus?
hi,
i would like ton make my personel home made cart for SNES with a 27c322.
can you tell me if my schéma is ok ?
http://sega4ever.power-heberg.com/tutod ... 20cart.png
thanks
X-death wrote:
hi,
i would like ton make my personel home made cart for SNES with a 27c322.
can you tell me if my schéma is ok ?
http://sega4ever.power-heberg.com/tutod ... 20cart.pngthanks
Untie pin 24 (SNESROM /CE) from ground, let the ground continue the same way. Remove the wire from pin 33 (SNESROM /OE) completely as it is the exact same as what is connected to the MAD-1 pin 4.. lol.
Wire pin 24 then to pin 3 of the 74ls_139. don't forget to ground the /ce, /oe, and 2 vpps of the 27c322 and to connect +5v to all the vcc points of the 139, 245s, and the 27c322.
Cheers
Also, and I should probably just PM Kyuusaku for help on this one, but.. I'll try my luck on this thread first.
Would piggybacking another 27c322 onto the first one and connecting the lifted pin 13 (EPROM /OE a.k.a. GVpp) legs to the mad-1 as follows work out fine? I tried it and I didn't get it working.
http://nintendoallstars.w.interia.pl/romlab/mads.htm
So I used that link, connected the /OE's of the eproms to the mad-1 as followed. I also have a 48mbit cart of Tales of Phantasia and that is how they seem to connect it. Would the data lines still function correctly with the 245 setup?
Someone said maybe I should be tying the eprom legs of pin 11 of the 27c322 (/CE a.k.a. E) to the mad-1 instead.
Thanks in advance!
Cheers
Yeah you can piggyback, but you must separate the /CEs (everything else should be connected). Don't use ROMLab as a reference, it's all messed up.
Each ROMs is selected by its /CE using a decoder. MAD-1 has a decoder built into it, but it's a little more involved than the 139.
So right now you have one of the two decoders in the 139 selecting a 245 right? Use the other decoder to select which ROM's /CE is active.
You can do this by taking the /CE going to the current ROM, and hooking it to the 2nd decoder's /E input. From there connect the B input to GND and the A input to A22. The Y0 output should connect to the ROM containing the first 32M's /CE, the Y1 output should connect to the last 16M ROM's /CE.
^ Just for reference.
Right, my test cart is wired like that now, when i drop a 27c322 into the zif (just 1) it works fine! but when i stick the piggybacked 2 27c322 package with the 11th legs lifted and individually wired to the 74ls139, i dont get anything but a black screen.
EDIT: Got it working, but I grounded the E of the 139 (lol, screw saving energy? at this point)... Yea, only works when Y0 is connected to the ROM /CE of the eprom with 16mbits of data, and Y1 is connected to the ROM /CE of the eprom with 32mbits of data.. lol.
EDIT 2: Tied SNES /OE to E of 139, works!
EDIT 3:
Tested Working.
Leg 11 of 27c322 = EPROM /CE
Leg 13 of 27c322 = EPROM /OE
Pin 24 of Maskrom = SNES /CE
Pin 33 of Maskrom = SNES /OE
Pin 35 of Maskrom = A22
NC = Not Connected
Question for Kyuusaku
Is a 30awg tap for vcc and ground enough for 2 27c322's?
Pin 15 is tied to what? Hopefully the MAD-1's /CE output and not the console's /ROMSEL.
The way I told you to wire the 139 you cannot ground E, it's not about energy, it's about only enabling the ROM at the right time. Grounding it would cause one ROM to always be enabled and they will conflict with the console's work RAM (very bad).
The reason why "/OE" works is because it's not /OE! Again, don't use ROMLab as a reference, they have /OE and /CE reversed.
I'm not sure if 30awg is good enough. You can always put multiple wires in parallel if you don't have a better wire. Don't forget to wire in bypass capacitors too..
Every game works flawlessly.. (beat Terranigma and I am half way through Tales of Phantasia, Secret of Mana 2, and the ReTranslation of Final Fantasy 6). I have made and tested the saves for Bahamut Lagoon, Final Fantasy 5, Dragon Quest 1/2, 5, 6, Treasure of the Rudras, and a few more..
But Kyuusaku, I am on a venture to build a game that people have problems with - so I may be back lol
. (Did I tell you I love ya?)
Dragon Quest 3 is a 32mbit game, becomes 48mbit with its translation IPS applied. If you look
http://www.racketboy.com/forum/viewtopic.php?f=25&t=13416&st=0&sk=t&sd=a&start=400 you can see that these guys have problems saving. I will try it using the same method as Tales of Phantasia (piggybacking 27c322s). I hope it will work for me as that sram issue smells like incompatibility in the mad-1 pinout while using a 74ls138 + 6x8mbit eproms works fine.
Update: works fine for DQ3 according to the replies I got after i posted your 139 pinout lol (http://www.racketboy.com/forum/viewtopic.php?f=25&t=13416&st=0&sk=t&sd=a&start=410)
Random Blabbering:
"Right, MAD pin 13 going to cart pin 48 on the ToP cart, that's A22 on normal Hirom 36 pin carts. You can see the pinout here. It won't work without MAD pin 13 going cart pin 48/A22"
-electrochip (from
http://www.racketboy.com/forum/viewtopi ... &start=380)
Yeah, I don't mind wiring anything up to the 74ls139 because it has a decoder free. but that method also works where i previously said it did not. i did not notice pin 13 of the mad-1 is not connected to a22 on regular hirom 1 maskrom carts where it is on tales of phantasia.
So you can wire the rom /ce legs to pin 1 and 16 of the mad-1 if you lift leg 13 and wire that to a22 as the quote above said and as the schematics of the original pcb show.
This is definitely the cheapest method to produce any game repro. IMHO It is a very simple job to solder this up - but very time consuming due to a lot of wires being needed. the 29f032 with top40 to dip36 adapter method seems easiest of course - and not that hard to make an adapter, all you need is breadboard, a zif socket, and 3? wires lol..
Will this work with 74HC245???
Because I have no 74LS245, I would have to order them.
Edit: Have now ordered 10 x 74LS245.
I will try the 74HC245. They aren't so expensive.
Anyways if they won't work in Snes Carts, I can them use in Nes.
I will reply if they work
hi guys,
I want to built a TOP cart with 2x 27c322 inkl. Decoder and 74LS139 Decoder.
lunarcris has been post this information
Leg 11 of 27c322 = EPROM /CE
Leg 13 of 27c322 = EPROM /OE
Pin 24 of Maskrom = SNES /CE
Pin 33 of Maskrom = SNES /OE
Pin 35 of Maskrom = A22
if i would use only one 27c322 i could set Pin 11 and 13 to gnd and it would works.
What if i use 2 x 27C3222 eproms?
On the image
ROm2/Ce is connected to Decoder Pin 12 and Rom1/Ce is connected to Decoder Pin 11.
Would this mean that i dont should solder the Pin 11 (CE) and 13 (OE) of the 27c322 to GND?! Because Pin 11 is connected to decoder!
I have understand, that if i want to built the game to a normal 1 maskrom hirom board like NHL 95/96 i have to solder on the following way
Decoder -> Solder to...
Pin1 -> SNES /CE
Pin2 -> Snes A0
Pin3 -> SNES/ OE
Pin4 -> 245 #1 Pin 19
Pin5 -> 245 #2 Pin 19
Pin8 -> GND
Pin11 -> Rom 1 / CE (is this Leg also connected to a other point?!)
Pin12 -> Rom 2 / CE (is this Leg also connected to a other point?!)
Pin13 -> GND ( like Pin8)
Pin14 -> SNES A22
Pin15 -> SNES /OE (like pin 3 on decoder)
Pin16 -> 5V
What is with the MAD-1 Pin 13. It is reqiured to lift the pin?!
Thanks in advance
red
Was the 27c320 ever made in DIP format or only in SO and TSOP?
I swear I was told there was DIP package versions of this chip
but can't seem to find any info on google,ect.
If it was, it's pretty rare to find one now. If it were available, we'd seen people using them.
Hi,
I am trying to build a SNES card based on 1 27C322, 2 74xx257 and only one 74LS139.
Here's a picture:
[/url]http://imageshack.us/photo/my-images/11/61748144.jpg[url]
I have an 1J3B-01 4MB Hirom board with an 74ls139 as Sram decoder and 64k Sram.
This is how its connected by Nintendo.
Code:
A15 1 16 VCC
A13 2 15 Pin 7 of 74LS139
A14 3 14 A21
NC 4 13 A22
NC 5 12 NC
NC 6 11 SRAM Pin 20=/CE
Pin15 7 10 NC
GND 8 09 GND
How do I have to connect the 74LS139 when using 27C322 with 2 74xx257?
I really don't want to use an Mad-1 or a second 74ls139 as decoder.
Regards,
Michael
OK so which one of these schematics is correct?
I see tons of different info in this thread and
alot of pictures. I just want to make sure I'm
gonna follow one that when I print it out it
will be correct. Thanks in advance.
kyuusaku wrote:
The ROM is 16-bit wide but file data is addressed sequentially in 8-bit bytes, so the "endianness" determines which byte is placed in the upper and lower 8-bits of the 16-bit word. The circuit is configured for big-endian data (even bytes are D15-8), but there's a good chance the Willem software chose little-endian. But if this is the case, you don't need to reburn the ROM (normally you would), you just need to exchange 139 pins 4 and 5 which in effect swaps bytes.
Digging up an older post here.....
Kyuusaku, is this the benefit of using the 245+245+139 over the 257+257+32 design?
Or is there a way to easily swap the endian-ness of the data lines that I'm not seeing?
Is it very common for programmers to swap endian's or is that a quirk and nothing to be alarmed about?
nintendo2600 wrote:
OK so which one of these schematics is correct?
I see tons of different info in this thread and
alot of pictures. I just want to make sure I'm
gonna follow one that when I print it out it
will be correct. Thanks in advance.
This works for me.
THANK YOU to ALL who advised me on this. I learned a lot!
The jumper shown on the pic is for smaller than 32mbit roms. The jumper is necessary for the smaller roms (i.e. 27c160) to keep the rom in 16bit mode. IF you never plan to use a smaller than 32mbit rom, then you can hardwire that line to the rom or use the SL (solder lug) as shown.
