Help with 16 Bit Program Counter

[cu44]

Hi all,

First a little background. I am reading "The Elements of Computing Systems"
and one project was to build a 16 bit program counter but having a tough time.
I am reading for pleasure not for any course. The following pc hdl file gives me the proper output (listed below pc file) up to time 3+ the gets off track and can not seem to figure it out. Any help/guidance would be greatly appreciated.
Thanks, Paul

// This file is part of the materials accompanying the book
// "The Elements of Computing Systems" by Nisan and Schocken,
// MIT Press. Book site: www.idc.ac.il/tecs
// File name: projects/03/1/PC.hdl

/**
* 16-bit counter with load and reset controls.
*
* If reset(t-1) then out(t) = 0
* else if load(t-1) then out(t) = in(t-1)
* else if inc(t-1) then out(t) = out(t-1) + 1 (integer addition)
* else out(t) = out(t-1)
*/

CHIP PC {

IN in[16], load, inc, reset;
OUT out[16];

PARTS:


Mux16(a=regOut1, b=false, sel=reset, out=rOut);
Mux16(a=rOut, b=in, sel=load, out=regOut);
Register(in=regOut, load=load, out=regOut1);
Inc16(in=iOut1 , out=iOut);
Register(in=iOut, load=inc, out=iOut1);
Mux16(a=regOut, b=iOut1, sel=inc, out=rOut2);
Mux16(a=regOut1, b=iOut1, sel=inc, out=out1);
Mux16(a=out1, b=regOut1, sel=load, out=out);

}

INPUTS AND OUTPUTS AT EACH TIME SEQUENCE

| time | in |reset|load | inc | out |
| 0+ | 0 | 0 | 0 | 0 | 0 |
| 1 | 0 | 0 | 0 | 0 | 0 |
| 1+ | 0 | 0 | 0 | 1 | 0 |
| 2 | 0 | 0 | 0 | 1 | 1 |
| 2+ | -32123 | 0 | 0 | 1 | 1 |
| 3 | -32123 | 0 | 0 | 1 | 2 |
| 3+ | -32123 | 0 | 1 | 1 | 2 |
| 4 | -32123 | 0 | 1 | 1 | -32123 |
| 4+ | -32123 | 0 | 0 | 1 | -32123 |
| 5 | -32123 | 0 | 0 | 1 | -32122 |
| 5+ | -32123 | 0 | 0 | 1 | -32122 |
| 6 | -32123 | 0 | 0 | 1 | -32121 |
| 6+ | 12345 | 0 | 1 | 0 | -32121 |
| 7 | 12345 | 0 | 1 | 0 | 12345 |
| 7+ | 12345 | 1 | 1 | 0 | 12345 |
| 8 | 12345 | 1 | 1 | 0 | 0 |
| 8+ | 12345 | 0 | 1 | 1 | 0 |
| 9 | 12345 | 0 | 1 | 1 | 12345 |
| 9+ | 12345 | 1 | 1 | 1 | 12345 |
| 10 | 12345 | 1 | 1 | 1 | 0 |
| 10+ | 12345 | 0 | 0 | 1 | 0 |
| 11 | 12345 | 0 | 0 | 1 | 1 |
| 11+ | 12345 | 1 | 0 | 1 | 1 |
| 12 | 12345 | 1 | 0 | 1 | 0 |
| 12+ | 0 | 0 | 1 | 1 | 0 |
| 13 | 0 | 0 | 1 | 1 | 0 |
| 13+ | 0 | 0 | 0 | 1 | 0 |
| 14 | 0 | 0 | 0 | 1 | 1 |
| 14+ | 22222 | 1 | 0 | 0 | 1 |
| 15 | 22222 | 1 | 0 | 0 | 0 |

 

[cu44]

Never mind I figured it out. thanks for looking.

 

[piercas]

Hi Paul,

It seems like you have made a lot of progress in building your 16-bit program counter. However, I can see that there are some issues with the output after time 3+. It would be helpful if you could provide more information about what you have tried and what specific issues you are encountering.

One thing that stands out to me is that you are using integer addition in your code. While this may work for some inputs, it may not be the most efficient or accurate way to increment the program counter. I would suggest looking into using binary addition instead.

Additionally, you may want to double check your Mux16 and Register components to make sure they are functioning correctly. It is possible that there may be a mistake in your code that is causing the output to become off track after time 3+.

I would also recommend breaking down your code into smaller parts and testing each component individually. This can help you identify any errors and make troubleshooting easier.

I hope this helps and good luck with your project!