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NEC V20 "-8" CPU clocked at 10MHz
- Thread starter Gustavo
- Start date
dhau
Experienced Member
why? ebay is full of 16MHz V20s for 2-3$ a piece
Chuck(G)
25k Member
I run a 5 MHz V20 at 8 MHz with no issues. It's the early CerDIP, so that may have some bearing.
I bet these are mostly fakes. I just checked a few on ebay and they all scream fake due to the printing that is identical to other fake chips, and the fact that the model number does not match with what a 16 MHz version should say. Finding (or rather: getting) a real one might require some luck.
kdr
Experienced Member
I run a V20 -8 chip in my 10mhz turbo XT machine, no issues at all with this particular chip. As with all overclocking your mileage may vary. If you've already got an -8 chip then why not give it a try and see what happens?
Ruud
Veteran Member
And it won't hurt to place a little fan. My 8087, with the correct specs, always became quite hot. OK, I could still touch it but still. Since I installed the fan, just a bit warm.
Eudimorphodon
Veteran Member
FWIW, I bought a tube of these cheap-ies after successfully upgrading two Tandy machines with them. They may well be "fake", IE, rebadged, but they at least seem to actually be V20s. Now what clock speed they're actually rated for is anyone's guess, all I know is they work up to 7.16mhz.
dhau
Experienced Member
Work fine in 12MHz Juko XT board too, and running very cool. Looking at the pins, it looks like they are genuine old parts de-soldered from some old PCBs. May be some Fax machine or photo-copier, who knows.
Eudimorphodon
Veteran Member
Yeah, they're definitely used, the pins have that suspicious tinned look to them, but at least they are mostly what they say they are. Could be from any number of things, I like to think mine are from old Pachinko arcade games.
Ruud
Veteran Member
The V20 is not 80286 compatible. It has some 80286 instructions like PUSHA and POPA but here the 80186 served as base. No idea how compatible it is with the 80186.
Games that I´ll try to run:
- Pinball Fantasies
- MS Flight Simulator 4 in 286 mode
- Magicland Dizzy (won´t detect VGA with any 8088 XT)
- Charlie the Duck
- Alone in the Dark (very slowly)
- Tubular World (don´t know if it requires 286 or 386)
- Alpha Waves (won´t run in my XT clone)
- Flashback
- Pinball Fantasies
- MS Flight Simulator 4 in 286 mode
- Magicland Dizzy (won´t detect VGA with any 8088 XT)
- Charlie the Duck
- Alone in the Dark (very slowly)
- Tubular World (don´t know if it requires 286 or 386)
- Alpha Waves (won´t run in my XT clone)
- Flashback
Chuck(G)
25k Member
The V20 actually has more instructions than the 80186; the basic set is identical between the two. However, there's the business of the 80186 and its integrated peripherals that can throw a cockroach into the spaghetti.
Eudimorphodon
Veteran Member
So far as I'm aware the V20 has the full set of 186 extensions... and this is on top of its own secret talents like being able to run 8080 binary code. Anyway, yeah, the reason people talk about having a V20 enabling you to run "286 software" is because the 286's Real Mode has the same extensions from the base x86 instruction sets as the 186. It's pretty common for DOS software dating from the early 1990s onward to have these instructions and choke on 8088/86 CPUs, having a V20 will unstick them. (Whether the software will run fast enough to be useful is another question, of course, but a V20 lets you at least try.) Obviously any software that uses 286 Protected Mode (via a DOS extender or whatever) isn't going to run.
Not an expert by any means, but part of my in-laws' estate that came to my wife is a for real Pachinko machine that was "liberated" from an officers' club someplace or other. The "restoration" mostly involved removing accumulated rodent and bug debris from the tracks the balls flew around on. But the only "electronic" parts were some sockets for 12v flashlight style bulbs and connective wiring that attached them to either a battery or a transformer that was long gone.
Short version, all mechanical with the exception of those lights & not the first IC to be seen V20 or otherwise.
Chuck(G)
25k Member
Note that, in addition to having 8080 emulation, the V20 has BCD string instructions as well as bitfield manipulation ones, neither of which the 286 and 186 have. The 80386 was supposed to have bitfield instructions (early manuals show them), but they apparently were dropped at the last minute.
Eudimorphodon
Veteran Member
If you get a hold of a full MAME ROM set and start randomly poking through the literally thousands of games you'll find a lot of Japanese electronic pachinko-and-pachinko-like arcade games. That's what I was referring to.
(Googling around I guess the one in particular I laughed my head off upon finding was based on an NEC V60, which is actually a completely different CPU from the x86-compatible V20-V50 series, but, hey, it did have an NEC V-cpu in it...)
... Also, for what it's worth, even "mechanical" arcade Pachinko machines that aren't from 1973 have all kinds of electronics in them. I mean, some of them look like this:
And a somewhat older one, with what looks suspiciously like 40 pin DIPs in the guts:
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Chuck(G)
25k Member
I was a big fan of the V60-V80 CPUs, which, curiously, also contain 8080 emulation mode. My take is that they were aimed at I-TRON, which never really caught on outside of Japan. Shame that. 