Jameco + nec v20

[bugman2112]

Just purchased a Jameco clone board with an NEC v20. Anyone have experince with this motherboard? I purchased it mainly as a backup board, and I always wanted to check out that NEC v20 chip. I'm curious if it came stock with the nec, or if that was added. They are pin compatable, right? So I should be able to put a 8088 back in at any time? I read that the nec is not 100% software compatable. What is nice is that it comes with a manual as well. I also noticed that this clone board, as well as most that I see for sale, is missing one of the two ROMS. I'm assuming that is the BASIC ROM to avoid copyright infringements? I doubt missing that chip would cause any compatability problems, expect of course if something like BASICA calls on the ROM. I don't think much software made calls to those routines?

 

[strollin]

I don't know anything about the Jameco board but have used the NEC V20 chip to replace quite a few 8088's on other boards. I haven't run into very many (if any) issues running the V20 and the machines get a slight speed increase.

ROM BASIC really isn't necessary because you can use GWBASIC from MS-DOS in place of BASICA to run any BASIC programs you want to run.

 

[Chuck(G)]

Generally, Jameco marketed rebranded generic Taiwanese clone boards. Most XT-class boards were designed to take the 8088, but a few "turbo" boards might require one of the high-speed variants, such as the 8088-1 (10MHz).

I prefer the V20 to the 8088, myself. At the same clock speed, it's faster, has most of the non-protected 80286 instructions (as well as some V20-unique ones) and can do 8080 emulation natively.

You can duplicate the IBM XT BASIC ROM (although the legality is a matter of debate) and use it in your clone. For that matter, you can also use the 5160 BIOS, though if you have a software-controlled "turbo" mode, you'll lose that.

 

[bugman2112]

Based on other things I read, I was really expecting more compatability porblems with the V20. But based on the positive feedback here, I'll probably try it out.

 

[bugman2112]

I'm curious, what are the rules for replacing a 8088 with the v20? Are they speed rated the same and you just replace based on rated speed? I thought a crystal had to be changed when using a faster chip. I understand the v20 is faster because it is more efficient. But what mods are necessary for what speed difference?

 

[strollin]

The V20 needs to be rated the same or faster. If you replace a 5Mhz 8088 with an 8Mhz V20, it will work fine but will still run at 5Mhz (4.77Mhz), not 8.

 

[bugman2112]

Thanks for the info. I was surprised that Jameco still carries this chip. It is Jameco part number #34358 If you read the data sheet, it even says (v20)

 

[SteveH]

I understand the v20 is faster because it is more efficient.

If you replace a 5Mhz 8088 with an 8Mhz V20, it will work fine but will still run at 5Mhz (4.77Mhz), not 8.

If you look at the instruction timings, you'll find that most V20 instructions take fewer cpu cycles to complete. I seem to recall this giving a processor performance increase of 2 to 2.5 times that over the 8088 (well, at least in the boxes I fitted them).

 

[bugman2112]

So most of you seem to concur that the compatability issues are minimal with the v20 chip? I know its a simple matter of swapping the 8088 back in. But I ask because I am still getting everything together for this system to use for vintage gaming and general tasks. As expected, I'm runnung into the usual complications and workarounds getting all the hardware and software to function reliably. If I thought the v20 had significant compatability problems I would probably just avoid it altogether to remove that as a variable (but I really like the idea of playing with CP/M using the v20 8080 emulation mode!). So far, the only specific compatability problem I've heard of is with Lode Runner.

 

[Chuck(G)]

If you look at the instruction timings, you'll find that most V20 instructions take fewer cpu cycles to complete. I seem to recall this giving a processor performance increase of 2 to 2.5 times that over the 8088 (well, at least in the boxes I fitted them).

The bottom line is that you still have to fight with memory and the bus. Regardless of anyone's specific speed test programs, my own experience says that on average, you'll see 15-20% improvement in a typical program mix, tops. With I/O-intensive programs, the improvement is closer to zero.

I've never seen a speed doubling in a representative 8088 application. If anyone's interested, I still have one of the earliest evaluations of the V20 vs. the 8088 in my files.

I may even have some NEC MicroNotes that call out NEC's own benchmark numbers in my files.

 

[bugman2112]

Yes, I'd like to read that if you could find it.

 

[SteveH]

I've never seen a speed doubling in a representative 8088 application.

I did start by saying "I seem to recall...". It's been 20 or so years since I last played with the v20 and I remember a figure of 2 to 2.5, but cannot remember how it was derived or if that was times increase, percent increase or what. Oh well, the old grey cells aren't what they used to be - maybe I need the human equivalent of a brain/processor upgrade...

:transformer:

 

[Chuck(G)]

I did start by saying "I seem to recall...". It's been 20 or so years since I last played with the v20 and I remember a figure of 2 to 2.5, but cannot remember how it was derived or if that was times increase, percent increase or what. Oh well, the old grey cells aren't what they used to be - maybe I need the human equivalent of a brain/processor upgrade...

I wonder if you were thinking about the speed increase of a 6MHz 80286 over a 4.77MHz 8088? It's possible that I remember because I exchanged a lot of information with NEC Natick about the V20 (Rich Naro was my contact).

While researching microcontrollers recently, I was pleasantly surprised to find that the NEC V-series name still survives in the V850 microcontrollers. The instruction set is completely different, however.

 

[hargle]

So far, the only specific compatability problem I've heard of is with Lode Runner.

So what's up with that?
The only reference I can see to this is from mike brutman's pcjr page. I suppose I could just ask him, but I'll ask in the forum here instead. Sounds like this could be patched to work though. If I didn't have a billion things on my plate, I'd totally dig into that.

I too would like to upgrade at least one of my 3 8088 machines (whoops, I have 4 now that I bought a Tandy1k) to a V20, but Lode Runner is a MUST HAVE on all of them.

 

[bugman2112]

Well I recieved two of these chips today. I carefully inserted them. Neither seem to work. The system doesn't make any error beeps. I dont have video because my VGA card needs to be set after booting. I'll have to put back my CGA card to see if any messages are appearing. I removed the co-processor just to make sure there wasnt a problem. I should note these are 8mhzt chips replacing the 5mhzt 8088, but that should be ok as someone here indicated?

 

[Chuck(G)]

Well I recieved two of these chips today. I carefully inserted them. Neither seem to work. The system doesn't make any error beeps. I dont have video because my VGA card needs to be set after booting. I'll have to put back my CGA card to see if any messages are appearing. I removed the co-processor just to make sure there wasnt a problem. I should note these are 8mhzt chips replacing the 5mhzt 8088, but that should be ok as someone here indicated?

Faster should be fine. Make sure you haven't bent a pin or stuck one in backwards.

 

[bugman2112]

I double checked that. I was very careful and tried multiple chips. Upon extraction, all pins were perfectly straight. Re-inserting the 8088 resulted in a booting PC once again. Stumped here unless they are bad chips. They look like old-new stock though. I've got one more in the mail already on a tested motherboard. I can try that one out.

 

[Chuck(G)]

Jameco doesn't sell junk, but you never know on some of these old chips.

 

[mikey99]

I picked up an XT clone board with a NEC V20 awhile back (pic below).
This sounds similar to the board mentioned above.
When I saw the -10 on the CPU I thought this was a 10 Mhz Turbo XT
but no, it only runs at 4.77

 

[modem7]

Well I recieved two of these chips today. I carefully inserted them. Neither seem to work. The system doesn't make any error beeps.

This happened to me about 6 months ago in an IBM 5160. I put the 8088 back in - system booted. Put the V20 in - system wouldn't start. Discovered that I could use the V20 only if the AST SixPackPlus board was removed.