View Full Version : Hardware simulators

May 10th, 2017, 10:21 AM
Recently I came across LT SPICE and downloaded it. I have never used or knew of simulators like this. I wanted to test some new chip select circuitry. After a short time I believe I got SPICE to work. BUT... I think LT SPICE is a linear tool and not that good as a digital tool. Now that I know there are such things, there must be other simulators that work well with digital circuits. I would like a simulator that has a TTL 7400 library in it. Anyone know of a 'free' simulator? Thanks


May 10th, 2017, 10:23 AM
There are a handful of TTL simulators out there, but there don't seem to be many good ones, that I've found. I've yet to find one with a particularly comprehensive component library.

May 10th, 2017, 10:34 AM
When I saw the title of this thread, I thought that you were talking about hardware-hardware simulators, such as those marketed by Zycad. When they first came out, they were freakishly expensive (6 digits). I see that Recycled Goods has a later unit (https://www.recycledgoods.com/zycad-101291-xp-140-simulation-accelerator/).

Does anyone collect these things/

May 10th, 2017, 08:43 PM
Proteus (https://en.wikipedia.org/wiki/Proteus_Design_Suite) can simulate 74xx logic "from the box". It also contain many popular CPU and microcontroller such as 8051, Z80, PIC, AVR ATMega, 8086 (sic!). Many popular device like 7-segment LED indicators, buttons, SRAM, LCD also included. So, you can easy build your own CPU (or TTL) based homebrew computer in Proteus. Unfortunately, it's no free. Proteus so good for digital simulation, but not good for analog sim (LT SPICE prefered).

May 11th, 2017, 06:22 AM
Thanks for the replies. Proteus looks good, but not priced for a SSA recipient. I also saw PSPICE, that one also looks good, but I bet it costs also. I may try something called Cedar. Still investigating. Mike

May 11th, 2017, 09:16 AM
I know, USA is no-tolerant with pirate softtware, and Russia today too, but.. torrent still avalible on Google. For non-comercical purpouse of course...
Sorry if i corrupted forum lows. Pls deleate this post if i say more.

May 11th, 2017, 02:03 PM
This afternoon I was out driving the Model T and stopped at a garage sale. I found a book titled "The Principles of Computer Hardware" 3rd edition by Alan Clements. Looks like a nice book and I got it for a dollar. The bonus was that there is a CD in the back cover and there is a logic simulator on it, called Digital Works. This version is for Windows 95. So I nosed around on the net and found a free version that will work on XP. So far I made a half and full adder and some chip select circuits. There are some more complex items, but I have not investigated that yet. So, I think I have something that may fill my needs and at my price. Let you know more about it as I learn. Mike

May 11th, 2017, 02:53 PM
Logic level simulators are usually not timing accurate. In order to make them truely timing accurate you have to analog simulate a silicon feature level description of the digital device. Similar to the component attributes in the LTSPICE library for analog devices (eg BJT), a lot of information is needed from the manufacturer. Many simulators allow rough entry of propagation times for devices. But usually even those are not uniform - often having different times for each type of input and each signal permutation to outputs. For example 0->1 may be 20ns, 1->0 maybe 25ns, and OE -> tri-state maybe 50ns.

In an HDL like Verilog, you can add artificial 'time units' to each RTL assignment then define a time scale. This allows general synthesis tools to do an approximate timing level simulation if there isn't a specific device and route plan specified for a real CPLD/FPGA.

If you want to try digital simulation programmaticly, I've used Verilator with some success to functionally verify digital designs. It does support #<time unit> syntax for assignments and will delay output transitions according to your time-scale.

May 11th, 2017, 03:39 PM
Thanks for the response. I'm not sure I'm up to that level yet. Most of my circuits are slow anyway, 7400 series stuff. I do like your quote at the end of your post. When I was a young engineer, back in days of yore, my new boss gave me the "Standard Handbook for Electrical Engineers", copyright 1922. It has more than 2000 pages in it. I bet that it would make a good throwing object as you mention. I never did use it for much other than some of the tables. Mike