Mike's PCjr Page

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?

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.

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

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.

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

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

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.

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.

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.

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.