Drop-in NEC V20 CPU Emulator with EMM and MicroSD

Drop-in NEC V20 CPU Emulator with EMM and MicroSD - MCLV20_Max

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First post, by MicroCoreLabs

Posted on 2024-12-27, 17:09

MicroCoreLabs Offline

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I would like to share my MCLV20_Max project which is a V20 drop-in replacement CPU for XT's that also contains 4 MB of Expanded RAM and MicroSD hard drive support.

Is has a number of features added to my MCL86+ project which include:
- 80188 and V20 new opcodes and bug fixes to the 8088
- 4 MB of Expanded RAM using a PSRAM on the Teensy 4.1
- MicroSD hard drive support using the slot on the Teensy 4.1 board so files are accessible via FAT16 on any computer.
- 640 KB of mirrored conventional memory accessible at the Teensy 4.1 native 800 Mhz + speed.
- Can host any BIOS or diagnostic ROM.
- Boots as cycle accurate by default and provides two acceleration modes:
#1 Boosted-speed which disables clock accuracy and doubles the performance over the 8088.
#2 Max-speed which copies all motherboard RAM into the Teensy where it is accessed at the maximum Teensy speed of 800 Mhz+ and improves speed by 5-10X.

More information on the VCF Forum: https://forum.vcfed.org/index.php?threads/dro … 20_max.1251110/

Reply 1 of 4, by weedeewee

Posted on 2024-12-27, 20:34

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Nice.

I see it only runs at 4.77MHz at the moment.

What will be the highest possible clock frequency that it will eventually might run at ?

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Reply 2 of 4, by BinaryDemon

Posted on 2024-12-27, 21:22

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Very cool. Could be fun to try WolfensteinCGA or Doom8088 on it.

Reply 3 of 4, by MicroCoreLabs

Posted on 2024-12-28, 00:28

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weedeewee wrote on 2024-12-27, 20:34:

Nice.

I see it only runs at 4.77MHz at the moment.

What will be the highest possible clock frequency that it will eventually might run at ?

The MCLV20_Max can only be used on a 4.77 Mhz motherboard due to limitations on the speed at which the Teensy can simultaneously controlthe local bus and emulate the CPU.

But internally it can run in accelerated modes many times faster than the original 8088/V20.

Reply 4 of 4, by Sneakernets

Posted on 2025-08-26, 18:08

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One man is destroying the ridiculously priced accelerator card eBay racket with this simple trick

...
I can't believe this was slept on for almost an entire year. Turning a stock XT into an XT286 with a drop in replacement is the kind of sorcery that will keep this hobby going. Why not go further? Throw 386 instructions in there. What's the worst that could happen? a bunch of eBay nerds can't sell their overly-priced accelerator boards? I can live with that.

A shame it can't be used on a Turbo XT, because the speed boost + faster ISA bus would be beyond hilarious.

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