Uncreative Labs

Joined: 20 Nov 2004 Posts: 589 Location: Shandong, China

I've been thinking about this subject for some time now. I think by now everyone is pretty familiar with the NEC V20 and V30 CPUs, as well as the various 80186/80286/80386 upgrade boards. But, I have been thinking about what other options there might be.

One method I was thinking about was building an 80186XL or 80188XL adapter. I believe these CPUs are available up to 33 or 40MHz, and I thought it would be interesting to implement a clock multiplier with this chip on an XT system. However, the 8018x chips are heavily integrated and I am not certain if it would be possible to adapt one to an 808x motherboard.

A second method I've been thinking about involves this elusive NEC chip called the V33. I learned about the V33 reading the newsgroups several years ago, and have been looking for one ever since. Just recently I was able to track down a V33A at 16MHz. These chips are ideal for using as upgrades since they don't integrate any motherboard components but have other enhancements that significantly speed up execution times. Many of the extra features would be useless, but the one that really stands out is that all CPU functions are implemented by hard wiring rather than though microcode. NEC used the "hard wiring" technique for the mulplication function in the V20 and V30 which is supposedly what really gave them an edge over the 8088 and 8086. NEC claims the V33 has similar performance to an 80286 at the same clock speed.

Some of the other interesting features of this chip include:

-CMOS technology
-both 8-bit and 16-bit databus compatible
-separate data and addressing busses
-24-bit memory addressing (special CPU mode)
-support for some kind of NEC FPU (vapourware?)
-Integrated LIM 4.0 support

However, the separation of the data and address bus poses a small problem. The 8088 and 8086 "multiplex" these two busses, meaning some additional support chips are likely required to interface with an 8088 or 8086 motherboard. I've been having similar problems adapting an 80287 to an 8087 socket fore the same reasons.

Right now the biggest obstacle is the fact that I can't find the datasheet for this chip. It seems the NEC V series datasheets are notoriously difficult to find. By chance I stumbled upon a V53 datasheet, but unfortunately this it the integrated version of the V33 and isn't terrible useful to me to determine the pinout of my chip. So, if anyone knows how to get this information please help me!

Joined: 19 Apr 2006 Posts: 261 Location: WisConSin

I recommend asking here classiccmp.org

They can be a grumpy group at times but occasionally there is someone there not bitching about their Dec long enough to give a usefull reply to something not DEC or british PC related.

I believe this paticular idea has been gone through before but there is some basic incompatibility with the XT in general that cannot fudged. I can't remember what the issue was but I believe even if you duplicate the tech similar to a 386sx to 286 cpu upgrade and get the signals happy there is another issue that prevents the system from entering post. That reason is also why you probably can't find a commercial equivalent.

Sorry I can't help more

Good Luck

Joined: 20 Nov 2004 Posts: 589 Location: Shandong, China

I managed to find all of the electrical datasheets for the V series of CPUs using Chinese search engines. The V33 is certainly a strange chip. It is advertised as a "super" version of the V30, which I interpreted to be somewhat pin compatible with the V30. Unfortunately this is not the case. The V33A pin functions are quite a lot different, and I think a lot of additional logic would need to be provided to interface with an 8086 or 8088 computer. Additionally, I'm not exactly sure if the V33 is capable of interfacing with an 8087 floating point unit. There are no provisions given in the manual for interfacing with this chip. Instead there is some documentation for linking up with some kind of NEC FPU. I only have partial documentation for the NEC FPU (just pinouts), so I really don't know if this chip is compatible with 8087 or not. It only mentions being compatible with IEEE754(?) standards.

I'm willing to give this conversion a shot, but I want to start out with some easier things first. I think I'll begin with my cache SMD to DIP SRAM adapters, and then my 80287 - 8087 adapter, and we'll see how that works out first.

Joined: 19 Apr 2006 Posts: 261 Location: WisConSin

Perhaps a better source of info would be the emulation / arcade folks since this chip was primarily used in certain arcade setups along with the usual embedded aps. (not to mention if you could find one cheap you could see what the chip required in the wild)

Good Luck, I think getting a v33 on an XT would probably need an ISA processor card w/ ram sockets and then an interface somewhat like a 286 aboveboard to plug into the XT 8088 socket.