View Full Version : Can I replace an Intel 8086 with a NEC V30, if an 8087 coprozessor is installed ?

Peter z80.eu
March 22nd, 2017, 10:27 AM
For several reasons (not only because of a small speed increase, but also because of the ENTER/LEAVE cpu op-codes) I like to replace an Intel 8086 with a NEC V30, but in this Amstrad 1640 PC, an Intel 8087-2 coprozessor is also installed.
I am now NOT sure if a NEC V30 CPU will work troublefree with an Intel numerical coprozessor, also because there was a NEC version of the coprozessor also. Also, the current installed Intel 8086 has a cooling element glued on it, because there is a small additional circuit installed beside the mainboard for switching 4.77Mhz, 8Mhz and 9.54Mhz (and I guess the 9.54Mhz frequency will warm up the main processor faster). The replacement V30 is a 10Mhz version, which should not need an additional cooling element on it...
So will I get in trouble when replacing the 8086 with the V30 ?

A Fox
March 27th, 2017, 07:38 AM
will a V30 work with a 8087? yes, its a drop in replacement (defiantly works with a V20 from experience, V30 should be the same). will a V30 work with THAT 8087? depends. The 8087-2 is an 8MHz part so in theory will only work up to 8MHz, this will work fine if you run the system at 8MHz. now obviously this system has been overclocked to 9.54MHz from your description so that chip must have been tested to that speed (though it is running outside of its spec) so as long as you don't try to increase the clock to 10MHz it should work fine but there's always the possibility that with a different CPU some subtle change may make it unstable at the 9.54MHz speed as that is out of spec for the chip. so what can be said is that it WILL work at 8MHz it MAY work at 9.54MHz but is almost guaranteed to NOT work at 10MHz (from what I have heard 8087s don't overclock well) if you want to put the speed up to 10MHz then you would ether need a 8087-1 or the NEC equivalent.

March 27th, 2017, 10:04 AM
I use an 8087 with my V30 all the time when running a graphing program. Works fine here.

Rick Ethridge
March 27th, 2017, 02:03 PM
My Tandy 1000 SL works fine with V30/8087.