NEC V20 Question

Hardware questions and modifications

NEC V20 Question

Postby Tempest » Tue Mar 10, 2015 9:22 am

When searching for a NEC V20 chip to upgrade the jr, what should I look for? I've been scouring ebay and I see several V20's listed, but I'm 99% sure most of them are not what I need. Is the important thing to make sure that it's a vanilla V20 running at 5MHz? Anything I should watch out for or avoid?
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Re: NEC V20 Question

Postby James » Tue Mar 10, 2015 12:37 pm

Any 8 or 10 Mhz one should work as well. The speed rating is the maximum speed. Standard V20s have the same form factor as the 8088.
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Re: NEC V20 Question

Postby GHiero » Tue Mar 10, 2015 7:39 pm

Make sure you don't overlook the obvious, are you sure your 8088 is socketed in your PCjr? Most are, some aren't.
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Re: NEC V20 Question

Postby Tempest » Wed Mar 11, 2015 10:35 am

GHiero wrote:Make sure you don't overlook the obvious, are you sure your 8088 is socketed in your PCjr? Most are, some aren't.


That's a good point. I'll have to take a look.
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Re: NEC V20 Question

Postby geoffdaddy » Thu Mar 12, 2015 8:59 am

Mine wasn't socketed when I checked it. Nevertheless I put a socket in and it's running a V20.
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Re: NEC V20 Question

Postby Tempest » Fri Mar 13, 2015 6:20 am

Mine is socketed. :)

Oddly enough I see a lot of NEC V20HL chips, but not many plain V20s. IS the V20HL compatible with the jr? Does it act like a regular V20?

http://www.ebay.com/itm/1pcs-D70108HCZ- ... 1349355121
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Re: NEC V20 Question

Postby jmetal88 » Fri Mar 13, 2015 8:23 am

Tempest wrote:Mine is socketed. :)

Oddly enough I see a lot of NEC V20HL chips, but not many plain V20s. IS the V20HL compatible with the jr? Does it act like a regular V20?

http://www.ebay.com/itm/1pcs-D70108HCZ- ... 1349355121


According to Wikipedia, "The NEC V20HL (μPD70108H) and NEC V30HL (μPD70116H) were high-speed (up to 16 MHz) and low-power versions."

So it sounds like something akin to the difference between a regular 7408 and a 74LS08. In other words, it should be completely compatible, but they just used different techniques putting it together that make it faster and more efficient.
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Re: NEC V20 Question

Postby Tempest » Fri Mar 13, 2015 8:46 am

That's what I thought from reading the wiki article, but I wanted to be sure.

I've asked this question before, but has anyone run into any games that won't work or play too fast with the V20? While speeding up slow games would be nice, I don't want to make older games play too fast.
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Re: NEC V20 Question

Postby GHiero » Fri Mar 13, 2015 10:09 pm

Some games intentionally run with shorter timing loops when they detect a PCjr. like Lode Runner. They think the system has 128KB and thus is slower than a PC, hence they speed the game up for a jr. Lode Runner is a good example of a game that does this. With the V20, you have speed up the system a small but noticeable bit. Nothing should be unplayable, but you might feel you are playing on the Hard difficulty level compared to playing the game on a PC.
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Re: NEC V20 Question

Postby Tempest » Tue Mar 17, 2015 6:07 am

Well if the V20 is going to mess up the game timings then maybe it's not worth it to me. I'd rather a game play a little slow than too fast.
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