Re: Why we like abstraction

Posted by monsonite on Jun 25, 2014; 2:18pm
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/Why-we-like-abstraction-tp1914023p4028182.html

Mark

Thankyou for pointing me in the direction of Logisim.  

I've tinkered with it for about an hour, and already got most of an ALU slice put together. I'm hoping to simulate the timing delays of the proposed ALU and possibly look at Carry Look ahead logic to speed up the arithmetic.

If any hardware enthusiasts are looking for a challenge... I've come up with a proposal for a bitslice version all in TTL - called Nandroid

I've also done an eagleCAD schematic for a more complete bitslice, which includes the D Register, the A register, the PC (and associated incrementer), and the two multiplexers.

The first iteration is intended to be made entirely from 74xx00 nands and 74xx74 for the registers.

There are a total of 18 chips in each slice,  and it looks like it would fit easily onto a 4" x 2" pcb using soic packages of the ICs. The slice would also include LEDs to show the status of the register bits (using the /Q output of the 74xx74) and a toggle switch register to allow simple programs/data to be toggled in - just like the old PDP8s.

The 16 slices connect together using double ended header pins, making an Arduino "shield like" construction.  This would leave a RAM/ROM pcb to include, and some sort of a PC interface - such as an Arduino MEGA, which has enough I/O pins to dump data directly into a 64K x 16 RAM. (To emulate  the ROM).

I may never get around to building this HCTTL implementation - as I think I would be better to concentrate on moving on to FPGAs, but it would be a great nostalgia piece.


Ken