The original PDP-11/Hack was an attempt at designing a minimal PDP-11 based on a discarded J-11. The J-11 is a microprocessor a bit similar to a 16-bit M68000 or a fast I8086.

http://madrona.ca/e/pdp11hack/index.html

Since that time, many people have made variations on Brent Hilpert design. One of my sources of inspiration is:

https://www.5volts.ch/pages/pdp11hack/

My design has the following features, but I never instantiated it:

* Much more RAM, 512KW

* The data bus is buffered (it is not in other designs)

* It has a GPIO (65C22) (because why not?)

* It can write into the upper byte

* The UART is the 6402, as in Brent Hilpert schematics, but the address is fully decoded to enable using a DEC OS.

* It has 5 switches to test/learn to single-step the memory accesses, the HALT, interrupts, or make a reset

* The boot configuration could be set up with micro-switches