ReproX: my $2 DIY repro pcb for simple mapper NES games Q&A

[game-tech.us]

I'm gonna start this thread and link ppl to it that email me with questions so all can see and interact etc.

About the ReproX pcb, it's my version of an all in one diy board for these discrete mappers:
NROM, CNROM, Panesian CNROM, UNROM, UOROM, ANROM, AMROM, AOROM, BNROM, GNROM, and MHROM.

It's for sale here:
https://www.game-tech.us/product/reprox/#reprox-pcbs

50 board volume discount as well:
https://www.game-tech.us/product-catego ... ion-parts/

[silentadminz]

First off the boards do work very nicely, easy to use for a newb just starting out.
However, I believe I noticed/found an issue with UNROM/UOROM directions. I put Contra on a M27C1001 (32pin 1m) Eprom, Megaman on a AM27c010, Castlevania on a M27c1001 , Paperboy ...etc and the games work without soldering jumpers E and J at all. Games play flawless and able go to the next stage...etc.

I actually ruined the contact on one of the E pads on another board from desoldering it so much during testing (My fault obviously, I'll use it for another type of test board). Can you think of a reason why it still works without Touching Jumpers E/J on the 32pin eprom listed above?

Pics attached.

Side Note.
This is probably not a question for this thread, but would still be nice to know. "if someone can shed some light on how to identify a pin being 'Tied High/Lo' that would be awesome"

[lidnariq]

game-tech.us actually explains why it's working on the "how to use" page...

E and J control whether pin 1 on a 32-pin ROM is pulled high, low, or ... if unpopulated, left to float.

Not all ROMs care about what pin 1 is doing. The ST microelectronics M27C1001 datasheet I have says that pin 1 can be "VCC or VSS" during normal operation. I wouldn't be surprised if the physical hardware only distinguishes between "Vpp voltages" and "enough less"—and while leaving the pin to float probably draws extra power, it's evidently functional.

[silentadminz]

game-tech.us actually explains why it's working on the "how to use" page...

E and J control whether pin 1 on a 32-pin ROM is pulled high, low, or ... if unpopulated, left to float.

Not all ROMs care about what pin 1 is doing. The ST microelectronics M27C1001 datasheet I have says that pin 1 can be "VCC or VSS" during normal operation. I wouldn't be surprised if the physical hardware only distinguishes between "Vpp voltages" and "enough less"—and while leaving the pin to float probably draws extra power, it's evidently functional.

Game Tech asked me to post this question/feedback here specifically. Mind you this is one of my first experiences with repros. I'll be honest I'm not savvy enough with pinout and Hi/lo's. Perhaps I just need some education on it in laymen terms.

On the how to use page on his site it lists this for UN/OROM:
....
E 32 pin – check datasheet, if pin 1 needs tied high: 2-3, if low: 1-2, if NC no jumpers
J 28pin chips no jumpers, 32 pins check datasheet usually pull high (1-2) if it needs pulled low jumper 2-3
....

Aside from E - If I'm reading that right J with a 32 pin chip needs a jumper regardless of hi/lo on un/orom. Could be possible I'm misunderstanding, hence the post.

[game-tech.us]

This is likely the datasheet you need to read for the M27c1001:
http://pdf.datasheetcatalog.com/datashe ... mXvtxx.pdf

Page 3 table 3 shows the operating mode truth table, reference page 2 figure 2A, to which pins need to be pulled high or tied low. Notes at the bottom of the table shows what X means and Vil is low and Vih is high.

This is all how it's supposed to be used, but as you've found sometimes it will work if the pins are left floating or not tied high or low, but that condition could cause problems and it's just best practice to do what the chip manufacturer says.

It's unlikley that other chips of same type (eprom) and size but other maker will be different, but it's best to check.

[lidnariq]

Exactly.

Not all parts care about what pin 1 is doing. (Many do)

In most UV EPROMs, pin 1 is Vpp, and many UV EPROMs want pin 1 to be at +5V when powered but not being programmed. But at least some, such as the ST-manufactured one I have, don't seem to care. (Hence "Vcc or Vss")

Leaving the pin floating usually isn't good ... but given the logic function, it's totally possible that the only thing it's detecting is presence of Vpp or not. And in this specific case, where for normal operation it says pin 1 should be "Vcc or Vss", leaving the pin floating evidently works.

[silentadminz]

Thanks for helping to identify this. I just genuinely don't know.
So here's my stab at interpreting what you guys just said and the datasheet on the said m27c1001 showing VPP Pin1 as VCC or VSS during Read Mode, so bare with me

I google searched what each meant (Noob): VCC for positive volts, and VSS for ground. (Here's the stab) By such logic VCC is positive or Hi, VSS is ground/negative or Lo, and I can tie them both Hi or both lo and it should work within best practices? Or am I entirely wrong here?

I also looked at AM27C010 http://pdf.datasheetcatalog.com/datashe ... /mXsus.pdf stating basically the same thing for pin1 during read mode - X = Either VIH or VIL. Which also might explain why it too works left floating, but obviously needs corrected. Once I can solidly identify/understand what pin 1 should be pulled/tied per chip on datasheets I'll crack open a

[lidnariq]

I can tie [both ROMs' pin 1] both Hi or both lo and it should work within best practices? Or am I entirely wrong here?

It depends on the ROM, really.

Looking at the random pile of 27-series EPROM datasheets I have, it looks like later (≈larger) ones usually explicitly mark pin 1 as "either" during normal operation, but I've also found several that do care, albeit no UVEPROMs in 32 pin DIPs.

[silentadminz]

Does that apply only to the PRG ROM or also the CHR ROM/RAM (depending on Rom type). In this instance I'm using CHR RAM of course as the other chip on the pcb. I was assuming this related specifically to PRG ROM chips. Also, if it depends on the ROM as you've stated It's almost partially a guessing game it seems lol. I guess another valid question would be can any damage come to the chip/pcb from tieing E/J hi or lo when it shouldn't be?

[lidnariq]

I haven't yet found a datasheet that specifically states that the corresponding ROM wants Vpp to be tied low for normal operation, but I'm definitely not going to claim that one doesn't exist.

The behavior of pin 1 is a property of the ROM, not where it's being used.

(RAMs are different, and almost no NES games use a RAM larger than 28 pin anyway)

[Sabont]

Can these ReproX Pcbs be used to repair/restore to life a game cart which was damaged beyond repair? Like move all the components over to the ReproX pcb, and set the appropriate jumpers to have it act as the same mapper silk-screened on the original PCB?

[game-tech.us]

Can these ReproX Pcbs be used to repair/restore to life a game cart which was damaged beyond repair? Like move all the components over to the ReproX pcb, and set the appropriate jumpers to have it act as the same mapper silk-screened on the original PCB?

Mostly no, the orignal prg and chr chips are mask roms and not the same pinout as eproms used on the reproX.
If I remember correctly the lockout chip is also a different pinout.
The mapper chips would be the same, but that's about it.
Might be better find one that is the same mapper type and move the mask roms on that board.
You can find out what type yours is and what games have the same mapper on the bootgod website.
http://bootgod.dyndns.org:7777/home.php

[rainwarrior]

For that purpose It'd probably be a lot easier to just copy the data onto a new EPROM than use the original mask ROMs? I mean, maybe this is a ship of theseus question but how much of the board can be replaced before you aren't satisfied that it's "the same" anymore?

[tepples]

For that purpose It'd probably be a lot easier to just copy the data onto a new EPROM than use the original mask ROMs? I mean, maybe this is a ship of theseus question but how much of the board can be replaced before you aren't satisfied that it's "the same" anymore?

For copyright purposes, I imagine it's "the same" if and only if the original mask ROM is used.

[game-tech.us]

I've added a 50 board volume discount at $74.95 plus shipping.
https://www.game-tech.us/product-catego ... ion-parts/