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2600 cartridge pcb w/2732 eprom question

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I'm in the process of building an eprom cart for my homebrew 2600 game. Here's what I'm using:

 

Intel 2732A2 eprom

SwordQuest C011885 Rev F pcb (modified to accomodate the 2732 pinnout)

7404 hex inverter

 

My question concerns references to a capacitor in some of the cartridge building posts. Is this necessary? If so, what is it for? Where does it go? What size capacitor will I need?

 

Thanks.

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I'm in the process of building an eprom cart for my homebrew 2600 game. Here's what I'm using:

 

Intel 2732A2 eprom

SwordQuest C011885 Rev F pcb (modified to accomodate the 2732 pinnout)

7404 hex inverter

 

My question concerns references to a capacitor in some of the cartridge building posts. Is this necessary? If so, what is it for? Where does it go? What size capacitor will I need?

 

Thanks.

As I said in your duplicate post, it will work without any capacitors.

 

Putting some on won't hurt anything, however.

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As I said in your duplicate post, it will work without any capacitors.

 

Common practice is to put a 0.1uF capacitor (also called 100nF or a "104") between VCC and ground of each chip. Using one such cap on a small board with two chips is also probably okay. Even using no cap is "probably" okay, though the amount of electrical noise (and thus radio/TV interference) that will be generated without a cap may be substantial.

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As I said in your duplicate post, it will work without any capacitors.

 

Common practice is to put a 0.1uF capacitor (also called 100nF or a "104") between VCC and ground of each chip. Using one such cap on a small board with two chips is also probably okay. Even using no cap is "probably" okay, though the amount of electrical noise (and thus radio/TV interference) that will be generated without a cap may be substantial.

The 2600 already has caps internally running from Vcc-GND. Unless the chip is especially power-hungry, I would think the internal caps would be adequate.

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I also think that it is best to place a 100 nF capacitor between each VCC pin and ground. I would put one close to the inverters VCC and one close to the EPROMs VCC :)

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I also think that it is best to place a 100 nF capacitor between each VCC pin and ground. I would put one close to the inverters VCC and one close to the EPROMs VCC :)

Even AA's 2k/4k board has just one cap. Why would we need two?

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I also think that it is best to place a 100 nF capacitor between each VCC pin and ground. I would put one close to the inverters VCC and one close to the EPROMs VCC :)

Even AA's 2k/4k board has just one cap. Why would we need two?

 

You don't, it's total overkill.

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Even AA's 2k/4k board has just one cap.

True, but I would have used two caps :D

 

Why would we need two?

I didn't want to say it is needed. I just wanted to say that it is better.

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The 2600 already has caps internally running from Vcc-GND. Unless the chip is especially power-hungry, I would think the internal caps would be adequate.

 

RF noise is generated when the amount of current flowing in a wire (or PC board trace, or whatever) changes rapidly. If there are no caps on the cartridge board, then any momentary increase in its current consumption when address lines change will increase the amount of current flowing along the entire path from the cartridge's chips to the 2600's capacitors. Adding a 0.1uF bypass cap will allow most of the momentary current demand to be supplied by the bypass cap, thus reducing the length of the RF-emitting segment.

 

A lot of circuits will work just fine with most of the bypass caps removed, but the amount of RF junk emitted will be increased. For a board the size of the AA cart which just has two fairly simple chips on it, one cap is sufficient. Some fancier chips, however, require multiple caps per chip.

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The 2600 already has caps internally running from Vcc-GND. Unless the chip is especially power-hungry, I would think the internal caps would be adequate.

 

RF noise is generated when the amount of current flowing in a wire (or PC board trace, or whatever) changes rapidly. If there are no caps on the cartridge board, then any momentary increase in its current consumption when address lines change will increase the amount of current flowing along the entire path from the cartridge's chips to the 2600's capacitors. Adding a 0.1uF bypass cap will allow most of the momentary current demand to be supplied by the bypass cap, thus reducing the length of the RF-emitting segment.

 

A lot of circuits will work just fine with most of the bypass caps removed, but the amount of RF junk emitted will be increased. For a board the size of the AA cart which just has two fairly simple chips on it, one cap is sufficient. Some fancier chips, however, require multiple caps per chip.

I still wonder if even a single cap would make an appreciable difference on the recycled Atari board. They are small with short, fat traces for Vcc and GND. I've made quite a few carts from them with no caps at all, and I haven't noticed any RF interference on the television. I left off the metal shield as well.

 

Well, omitting caps might affect a nearby AM radio, but who cares about that?

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Thanks for the input folks. Since I bought the caps, I think I'll go ahead and install one just for kicks. BTW, what proggrammer do you guys use for burning the 2732s. I bought a Willem Dual Power and it's been nothing but a headache so far. Absolutely the worst instruction manual I've ever seen.

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