Design Goals

From 256 bytes to 512K RAM

Whilst a great cost pared design, the original MK14 did have some extremely annoying features. I would include the following in these:

Keyboard that I could only get to work with a compass point - and then only once!
No backing store (as standard) or non-volatile storage - typing in 225 bytes of programme everytime I wanted to play "Moon Lander" was not my idea of fun
Limited visibility of miniscule calculator display
Very limited amount of RAM
Inflexible address decoding if you were tempted to add more RAM or other I/O

So I decided to fix all these in my redesign. The V2.0 machine has the following features:

Original SC/MP processor and INS8154 I/O running at original 4.43 MHz clock speed.
Build option for original LED calculator display or rather more legible 0.3" LEDs
Keyboard that works, with proper keyboard switches
512K Rom, 512K RAM
Memory split into multiple images - 16 x 4K original memory maps AND 14 "high" memory modes with 32K RAM and 32K ROM in each image.
Multiple memory images effectively gives you multiple MK14s (at the flick of a switch). You can load 16 programmes each of which uses all the available RAM in the CPU memory map
Multiple images applies to the ROM too. You want the classic monitor with the "---- --" start-up display or the extended monitor with cassette interface support? No problem - have both!
Memory is battery backed, so once entered your programmes stay there, even when power has been removed.
All address decoding is implemented in a CPLD, so a firmware change gives whatever memory map you can dream up.
Patch area for adding custom hardware such as D/A, single step, MSF receiver etc.
CPLD is programmed in VHDL. This makes it easy to change and portable to another CPLD architecture for the V3.0 version an another 20 years time!.

The overiding goal I had was 100% software and hardware interface compatibility with the original. That means programmes run at the same speed, the memory map has the same aliases and the RAM I/O works exactly the same as it always did. The extended memory modes let you do more (in a fully decoded 32K+32K), or you could map more RAM by removing some of the ROM repeats in the original 4K image by changing a couple of lines in the CPLD VHDL code.