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PC Building Yoshi
PostPosted: Thu Dec 22, 2022 5:32 pm 
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The only physical Component for my 8-Bit 6502 computer project is a Windbond W27C512-45Z EEPROM. While reading the Datasheet for it, the OE/VPP (Pin 22) is used for several different things, Including the Read and Modes. I do not want to use the Erase Mode, I only want to use the Read Mode so the CPU can read the Machine Code stored within the ROM.

So what do I do with the OE pin? Do i just tie it low so the Output Enable is always active just like an ATMEL EEPROM?
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PC Building Yoshi
PostPosted: Thu Dec 22, 2022 5:37 pm 
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Bonus Question:
I'm also using a AS6C1008-55PCB 128k SRAM IC, What should I do with the OE pin on it as well?
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GARTHWILSON
PostPosted: Thu Dec 22, 2022 6:41 pm 
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As long as the OE/Vpp pin does not go significantly above 5V, you won't accidentally erase or program the part.  To erase or program it, you have to take OE/Vpp more than twice that voltage.  The truth table is on page 7, and shows that to read, OE/Vpp and CE must both be low.  If either one is high, the device won't try to put data out on the bus.  However, if CE is kept low, the device will take more power-supply current; so if that's important to you, you'll want to make sure CE is high in bus cycles in which you're not reading it but rather addressing something else, whether RAM or I/O.

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PC Building Yoshi
PostPosted: Tue Dec 27, 2022 7:25 pm 
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GARTHWILSON wrote:
As long as the OE/Vpp pin does not go significantly above 5V, you won't accidentally erase or program the part.  To erase or program it, you have to take OE/Vpp more than twice that voltage.  The truth table is on page 7, and shows that to read, OE/Vpp and CE must both be low.  If either one is high, the device won't try to put data out on the bus.  However, if CE is kept low, the device will take more power-supply current; so if that's important to you, you'll want to make sure CE is high in bus cycles in which you're not reading it but rather addressing something else, whether RAM or I/O.


What happens when I pull OE/VPP to ground? Is that going to destroy the chip? And what happens when there is no voltage going into that pin?

From what I understood, it should be connected to +5v so it won't erase the Program data, so should I tie it to +5V, Ground or leave it alone entirely?
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GARTHWILSON
PostPosted: Tue Dec 27, 2022 7:53 pm 
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PC Building Yoshi wrote:
What happens when I pull OE/VPP to ground? Is that going to destroy the chip? And what happens when there is no voltage going into that pin?

There should be the overline over OE, but there's no way to do that on the phpBB forum software.  The way the "not" was shown in OrCAD which I used at my last place of work was to put the \ after it for "output-enable-not:" but I figured it would be too confusing to write "OE\/Vpp."  The \ followed by / looks like another capital V.  You must bring it low to enable outputs.  No choice.  So no, it won't damage anything.  That's part of normal operation.

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From what I understood, it should be connected to +5v so it won't erase the Program data, so should I tie it to +5V, Ground or leave it alone entirely?

You won't erase or program it at all if that voltage is kept in the normal operating range.  Programming (which is done with the separate EPROM programmer, not in-circuit) requires bringing it way up far above the normal operating voltage.  Without going to that high (+12V or thereabouts) voltage, low is for enabling outputs, and high (+5V) is for disabling outputs, and you might switch it even millions of times per second.

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The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?
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No True Scotsman
PostPosted: Sat Aug 05, 2023 7:58 pm 
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Use the pipe or exclamation mark for NOT if overline isn't possible: |OE or !OE. Any mutually agreed upon convention will do.

phpBB apparently has an overline BBCode, the letter O in square brackets. vBulletin appears not to have it. Someone familiar with the PHP source code could add it though:

Replace matches for this regex:

Code:
/\[o\]((?!\[\/o\]).*?)\[\/o\]/ms


... with this HTML:

Code:
<span style="text-decoration: overline;">$1</span>


There's likely more to it than that. The message parsers on these forum packages have to do a lot of gymnastics to handle nested tags, fix tagsets that the user forgot to close, etc. This would have to be done by someone invested in the package. I'm not the one. PHP forum code looks like spaghetti code to me.
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