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PostPosted: Sat Dec 08, 2012 8:40 am 
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I'm using the 29f032b flash rom on some of my carts. Question is, can the lower voltage flash roms be also used, assuming that an appropriate voltage regulator is used to drop down the power going to the flash Rom. Has anyone tried this?


Thank you
Mark


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PostPosted: Sat Dec 08, 2012 9:15 am 
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I've used 3,3V Flash on SNES carts. Just need an AMS1117 for Vcc conversion and a level shifter for the 8 Data Lines. Check the datasheet of the flash, some 3,3V Flashes are 5V tolerant so you wont need the level shifter.


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PostPosted: Sat Dec 08, 2012 9:20 am 
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The level shifter? Can you go into more detail about that?

Thanks!


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PostPosted: Sat Dec 08, 2012 9:36 am 
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A level shifter lets parts with different voltages "communicate" with each other, in this case it shifts 5V to 3,3V and 3,3V to 5V on the fly so a 3,3V flash can work in a 5V system. I use it to take a lot of load of the data lines which could damage the flash.


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PostPosted: Sat Dec 08, 2012 9:37 am 
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Can you suggest a part number I could look at?

Thanks


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PostPosted: Sat Dec 08, 2012 9:45 am 
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The 4050 is a good part for this, it can shift 6 lines at once.


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PostPosted: Sat Dec 08, 2012 9:57 am 
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Thank you. So I'd need 2 of these to shift the 8 bits, right?


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PostPosted: Sat Dec 08, 2012 10:07 am 
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Right, but first check the datasheet if you even need it. I think there was a 8x level shifter, I'll search for it and tell you the part no. if I find it.


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PostPosted: Sat Dec 08, 2012 10:08 am 
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Many thanks for your help. :)


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PostPosted: Sat Dec 08, 2012 10:45 am 
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I found a good one - it's the MAX3001E. It even does bi-shifting (shifting in both directions) and supports everything from 1.2V to 5V.


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PostPosted: Sat Dec 08, 2012 11:47 am 
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Sweet! Many thanks for your help.


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PostPosted: Sat Dec 08, 2012 12:27 pm 
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Non-5V tolerant ROMs will probably be damaged by the 5V on the address lines: I don't agree that it is only necessary to put a level shifter on the data lines.


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PostPosted: Sat Dec 08, 2012 12:56 pm 
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I took the data-lines-only comment to mean that some are 5V-tolerant on the address lines, but not on the data lines (since you'd need a level shifter to get 5V signals out of the data lines anyway). As always, check the data sheet for maximum ratings and do not exceed these.


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PostPosted: Sat Dec 08, 2012 1:49 pm 
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If you know of any 5v-tolerant flash ROMs in any decent sizes (32+Mbit) I'd be glad to hear about them. The best in-production parallel flash ROM line I've found are Micron's M29W chips (which are really re-branded SST parts). They have everything up to 2Gbit in 8/16-bit, but their entire line isn't 5v tolerant (I've even asked their tech support and they said definitely not). They do also offer the M29F line which is 5v, but only up to 8Mbit. You're probably going to need level shifters. You need bi-directional for the data lines, but everything else can be uni-directional (5v down to 3v). It's also a good idea to drive Vcc with a voltage regulator, though you could probably get away with a voltage divider (same goes for the uni-directional level shifting, but that's a lot of resistors to voltage divide 20+ pins...)


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PostPosted: Sat Dec 08, 2012 2:01 pm 
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For 32/64 MBit I use Intel Strata Flash parts 28F320J5 and 28F640J5. They were produced from 2007 (fairly new) for some years and it's not only 5V tolerant, it's a 5V part. They are available in SSOP package, so no need for adapters as it's fairly easy to solder by hand. The 64Mbit version is just 5$. For 128MBit, there's the "28F128J3D". It's a 3,3V part and it's adress & data lines tolerate up to 5,6V.


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