OR gates

[mstechca]

What I intend to do is make an EEPROM programmer for the chip AM29F010.

My design involves using 24 OR gates, one for each address bit (except A17, since A17 is 0 when sending the unlock code), and one for each data bit.

I have found that 10 1N4007 diodes cost me $1, and the flexibility is high when placing them on the circuit board.

In the basic sense, I can use two of them and connect the cathodes together to form a 2-input "OR" gate.

If I must use OR gate IC's I will, but if I can get away with 1N4007 diodes, I would rather do that, because it is cheaper.

The question is, is there A difference between making an OR gate from diodes, and using an or gate from a logic chip?

What would you recomend and why?
I don't want anything to overheat.

 

[justDIY]

I don't really have much to say about programming the eeprom, no experience there

but... isn't the 1n4007 a bit much for this application? I mean, its rated for 1 amp of current with 1000 volts breakdown ... that is a high voltage rectifier diode - I think you want a signal / switching diode?

Here's a good general purpose diode for logic circuits (1N914 equiv):
**broken link removed**

only 3 cents each

 

[Roff]

I can buy CD4071 from Jameco for US $0.28. That's 7 cents per OR gate. There may be cheaper ones available.
Jameco also has CD4011 (2-input NAND) for $0.20, which is a negative-input OR gate, if you have the complement input data available. Of course, you have to pay for shipping. If you can get the diodes locally, maybe it's a better deal.
I wouldn't try to use 1N4007 if the input transition times are fast, because the 1N4007 has significant capacitance (remember varactors?). This can cause slow fall times, and possibly glitches on the falling edge. You will also lose about 0.6V on your logic "1" levels. As mentioned by justDIY, 1N4148s are much better for logic.

I also have never built an EEPROM programmer. :cry:

 

[bryan1]

Hiya Mstechca,
Here's a link to a eeprom programmer siliconchip did back in 2002 https://www.siliconchip.com.au/cms/A_30475/article.html now take a look at the schematic then tell us you can do the same just using or gates :?: . Now why bother trying to re-invent the wheel when there's plenty of circuits out there to do the same thing your attempting.

Cheers Bryan

 

[ljcox]

The IC gates are better. I had a problem with a diode OR gate using the 1N4148 because of the stored charge. This causes spikes in the output which may cause problem - depending on where the output is connected.

 

[Dean Huster]

The only advantage to using 1N4007s as the logic is that you can have a HIGH of +800v with no problem at all, so wild logic levels are no sweat. But as Ron and others have said, speed is a problem. And I'd bet that the 14 diodes required to replace 7 IC gates would be bigger than the IC!

Dean

 

[justDIY]

The only advantage [...] a HIGH of +800v with no problem at all ...

jeeze Dean, you almost made me fall from my seat laughing with that one

i've heard of high voltage eprom before ... but 800v!

 

[mstechca]

HIGH of +800v

LOL :lol:

actually, I'm not going higher than 5V. and the outputs of the OR gates are connected directly to each address and data lines of the AMD's 29F010B.

 

[mstechca]

Hiya Mstechca,
Here's a link to a eeprom programmer siliconchip did back in 2002 https://www.siliconchip.com.au/cms/A_30475/article.html now take a look at the schematic then tell us you can do the same just using or gates :?: . Now why bother trying to re-invent the wheel when there's plenty of circuits out there to do the same thing your attempting.

Cheers Bryan

Look at the link. Look at the 3rd paragraph in the article.

Do you think I'm going to spend $300+ on one programmer when I could make one myself for under $50?

 

[ljcox]

Hiya Mstechca,
Here's a link to a eeprom programmer siliconchip did back in 2002 https://www.siliconchip.com.au/cms/A_30475/article.html now take a look at the schematic then tell us you can do the same just using or gates :?: . Now why bother trying to re-invent the wheel when there's plenty of circuits out there to do the same thing your attempting.

Cheers Bryan

Look at the link. Look at the 3rd paragraph in the article.

Do you think I'm going to spend $300+ on one programmer when I could make one myself for under $50?

But thanks for the suggestion Bryan1.

 

[Nigel Goodwin]

Does anyone have any idea what the OR gates are for?, it seems pretty pointless discussing diode OR versus IC OR when the entire premise might be completely wrong?.

Perhaps mstechca might like to post a block diagram of what he's trying to do?.

 

[DigiTan]

It sounds sort of like you're using the OR's as a bus enable line. If you can get a CMOS device, you'll have extremely low leakage current; as opposed to diode logic which generally depends on a larger current to create a TTL voltage across its output resistance. In general it could really go either way though. Just make sure all your diodes can safely dissipate the power they're going to take in.

 

[Roff]

Just make sure all your diodes can safely dissipate the power they're going to take in.

I hope you're joking. :shock:

 

[DigiTan]

In general. SMTs can melt faster than a slug in a salt mine.

 

[Roff]

In general. SMTs can melt faster than a slug in a salt mine.

:lol:
Maybe, but a diode in a logic gate is practically indestructible unless you make a wiring error or your probe slips. This is especially true of 1N4007, which is definitely not an SMT device, and is good for one amp continuous current.

 

[Styx]

am I the only one that voted for the diode option :?

For a single OR gate when I have none left in a package (or no packages put down of OR), a diode-OR wins on footprint. A SOT23+0603 package vs a 14pin SO packages plus decoupling...


no challenge really

 

[Roff]

am I the only one that voted for the diode option :?

For a single OR gate when I have none left in a package (or no packages put down of OR), a diode-OR wins on footprint. A SOT23+0603 package vs a 14pin SO packages plus decoupling...


no challenge really

Yeah, but I think he has LOTS of ORs. In that case, one SO14 and a decoupling cap would be replaced by four SOT23 dual diodes and four 0603 resistors.

 

[mstechca]

I was initially discussing OR gates because I would think they would be cheaper than multiplexers, but they are the same price (2-pack for $1). So I took it upon my self to by 8 (4 2-packs) 74HC157's so that I can manage every address and data bit. I'll use an AND gate for A17, since it must be 0 for programming mode.

I wanted to make my Flash ROM programmer, and I think there will be success.

Basically, I want mine to follow AMD's specifications, and literally write the programming bits everytime I want to write a byte. The multiplexers come in because the bit which adjusts the channel is the bit that determines whether I'm in initialization mode or actual data writing mode.

In Initializtion mode, channel 0 (see diagram) becomes active, and the data that is injected into the multiplexer is the correct code. I have discovered that alternating bits are inverted, and because of this, things are easier.
I will also add a clock which determines the "step" I am at in initialization. I will use 4 steps, just like AMD does.

I'll have to show a circuit. I think my diagram is too vague for you.

 

[Styx]

am I the only one that voted for the diode option :?

For a single OR gate when I have none left in a package (or no packages put down of OR), a diode-OR wins on footprint. A SOT23+0603 package vs a 14pin SO packages plus decoupling...


no challenge really

Yeah, but I think he has LOTS of ORs. In that case, one SO14 and a decoupling cap would be replaced by four SOT23 dual diodes and four 0603 resistors.

Ahh thats different then...