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Development of the MOS Technology 6502: A Historical Perspective

Jason Sachs June 18, 20222 comments

One ubiquitous microprocessor of the late 1970s and 1980s was the MOS Technology MCS 6502. I included a section on the development of the 6502 in Part 2 of Supply Chain Games, and have posted it as an excerpt here, as I believe it is deserving in its own right.

(Note: MOS Technology is pronounced with the individual letters M-O-S “em oh ess”,[1] not “moss”, and should not be confused with another semiconductor company,


Supply Chain Games: What Have We Learned From the Great Semiconductor Shortage of 2021? (Part 2)

Jason Sachs June 18, 20223 comments

Welcome back! Today we’re going to zoom around again in some odd directions, and give a roundabout introduction to the semiconductor industry, touching on some of the following questions:

  • How do semiconductors get designed and manufactured?
  • What is the business of semiconductor manufacturing like?
  • What are the different types of semiconductors, and how does that affect the business model of these manufacturers?
  • How has the semiconductor industry evolved over...

Reading and Understanding Profitability Metrics from Financial Statements

Jason Sachs March 29, 2022

Whoa! That has got to be the most serious-minded title I’ve ever written. Profitability Metrics from Financial Statements, indeed. I’m still writing Part 2 of my Supply Chain Games article, and I was about to mention something about whether a company is profitable, when I realized something that didn’t quite fit into the flow of things, so I thought I’d handle it separately: how are you supposed to know what I mean, when I say a company is profitable? And how am I...


A Second Look at Slew Rate Limiters

Jason Sachs January 14, 2022

I recently had to pick a slew rate for a current waveform, and I got this feeling of déjà vu… hadn’t I gone through this effort already? So I looked, and lo and behold, way back in 2014 I wrote an article titled Slew Rate Limiters: Nonlinear and Proud of It! where I explored the effects of two types of slew rate limiters, one feedforward and one feedback, given a particular slew rate \( R \).

Here was one figure I published at the time:

This...


Supply Chain Games: What Have We Learned From the Great Semiconductor Shortage of 2021? (Part 1)

Jason Sachs December 31, 20215 comments

So by now I’m sure you’ve heard about the semiconductor shortage of 2021. For a few complicated reasons, demand is greater than supply, and not everybody who wants to buy integrated circuits can do so. Today we’re going to try to answer some hard questions:

  • Why are we in the middle of a semiconductor shortage?
  • Why is it taking so long to get my [insert part number here]?
  • Did this shortage suddenly sneak up on everybody? If not, what were the signs, and why...

Definite Article: Notes on Traceability

Jason Sachs September 6, 2021

Electronic component distibutor Digi-Key recently announced part tracing for surface-mount components purchased in cut-tape form. This is a big deal, and it’s a feature that is a good example of traceability. Some thing or process that has traceability basically just means that it’s possible to determine an object’s history or provenance: where it came from and what has happened to it since its creation. There are a...


Painting with Light to Measure Time

Jason Sachs December 26, 2020

Recently I was faced with a dilemma while working from home. I needed to verify an implementation of first-order sigma-delta modulation used to adjust LED brightness. (I have described this in more detail in Modulation Alternatives for the Software Engineer.) I did not, however, have an oscilloscope.

And then I remembered something, about a technique called “light painting”: basically a long-exposure photograph where a...


Scorchers, Part 3: Bare-Metal Concurrency With Double-Buffering and the Revolving Fireplace

Jason Sachs July 25, 20201 comment

This is a short article about one technique for communicating between asynchronous processes on bare-metal embedded systems.

Q: Why did the multithreaded chicken cross the road?

A: to To other side. get the

— Jason Whittington

There are many reasons why concurrency is


Tolerance Analysis

Jason Sachs May 31, 2020

Today we’re going to talk about tolerance analysis. This is a topic that I have danced around in several previous articles, but never really touched upon in its own right. The closest I’ve come is Margin Call, where I discussed several different techniques of determining design margin, and ran through some calculations to justify that it was safe to allow a certain amount of current through an IRFP260N MOSFET.

Tolerance analysis...


Scorchers, Part 2: Unknown Bugs and Popcorn

Jason Sachs April 5, 20202 comments

This is a short article about diminishing returns in the context of software releases.

Those of you who have been working professionally on software or firmware have probably faced this dilemma before. The scrum masters of the world will probably harp on terms like the Definition of Done and the Minimum Viable Product. Blah blah blah. In simple terms, how do you know when your product is ready to release? This is both an easy and a difficult question to answer.

What makes...


10 Software Tools You Should Know

Jason Sachs May 20, 201215 comments

Unless you're designing small analog electronic circuits, it's pretty hard these days to get things done in embedded systems design without the help of computers. I thought I'd share a list of software tools that help me get my job done. Most of these are free or inexpensive. Most of them are also for working with software. If you never have to design, read, or edit any software, then you're one of a few people that won't benefit from reading this. 

Disclaimer: the "best" software...


Analog-to-Digital Confusion: Pitfalls of Driving an ADC

Jason Sachs November 19, 20118 comments

Imagine the following scenario:You're a successful engineer (sounds nice, doesn't it!) working on a project with three or four circuit boards. More than even you can handle, so you give one of them over to your coworker Wayne to design. Wayne graduated two years ago from college. He's smart, he's a quick learner, and he's really fast at designing schematics and laying out circuit boards. It's just that sometimes he takes some shortcuts... but in this case the circuit board is just something...


Help, My Serial Data Has Been Framed: How To Handle Packets When All You Have Are Streams

Jason Sachs December 11, 201110 comments

Today we're going to talk about data framing and something called COBS, which will make your life easier the next time you use serial communications on an embedded system -- but first, here's a quiz:

Quick Diversion, Part I: Which of the following is the toughest area of electrical engineering? analog circuit design digital circuit design power electronics communications radiofrequency (RF) circuit design electromagnetic...

Important Programming Concepts (Even on Embedded Systems) Part V: State Machines

Jason Sachs January 5, 20158 comments

Other articles in this series:

Oh, hell, this article just had to be about state machines, didn’t it? State machines! Those damned little circles and arrows and q’s.

Yeah, I know you don’t like them. They bring back bad memories from University, those Mealy and Moore machines with their state transition tables, the ones you had to write up...


Byte and Switch (Part 1)

Jason Sachs April 26, 201114 comments

Imagine for a minute you have an electromagnet, and a microcontroller, and you want to use the microcontroller to turn the electromagnet on and off. Sounds pretty typical, right?We ask this question on our interviews of entry-level electrical engineers: what do you put between the microcontroller and the electromagnet?We used to think this kind of question was too easy, but there are a surprising number of subtleties here (and maybe a surprising number of job candidates that were missing...


10 Circuit Components You Should Know

Jason Sachs November 27, 20113 comments

Chefs have their miscellaneous ingredients, like condensed milk, cream of tartar, and xanthan gum. As engineers, we too have quite our pick of circuits, and a good circuit designer should know what's out there. Not just the bread and butter ingredients like resistors, capacitors, op-amps, and comparators, but the miscellaneous "gadget" components as well.

Here are ten circuit components you may not have heard of, but which are occasionally quite useful.

1. Multifunction gate (


How to Build a Fixed-Point PI Controller That Just Works: Part I

Jason Sachs February 26, 20127 comments

This two-part article explains five tips to make a fixed-point PI controller work well. I am not going to talk about loop tuning -- there are hundreds of articles and books about that; any control-systems course will go over loop tuning enough to help you understand the fundamentals. There will always be some differences for each system you have to control, but the goals are the same: drive the average error to zero, keep the system stable, and maximize performance (keep overshoot and delay...


Supply Chain Games: What Have We Learned From the Great Semiconductor Shortage of 2021? (Part 2)

Jason Sachs June 18, 20223 comments

Welcome back! Today we’re going to zoom around again in some odd directions, and give a roundabout introduction to the semiconductor industry, touching on some of the following questions:

  • How do semiconductors get designed and manufactured?
  • What is the business of semiconductor manufacturing like?
  • What are the different types of semiconductors, and how does that affect the business model of these manufacturers?
  • How has the semiconductor industry evolved over...

Ten Little Algorithms, Part 1: Russian Peasant Multiplication

Jason Sachs March 21, 20156 comments

This blog needs some short posts to balance out the long ones, so I thought I’d cover some of the algorithms I’ve used over the years. Like the Euclidean algorithm and Extended Euclidean algorithm and Newton’s method — except those you should know already, and if not, you should be locked in a room until you do. Someday one of them may save your life. Well, you never know.

Other articles in this series:

  • Part 1: