WEBVTT NOTE This file was exported by MacCaption version 7.0.13 to comply with the WebVTT specification dated March 27, 2017. 00:00:11.470 --> 00:00:15.766 align:center line:-1 position:50% size:37% Serial buses are ubiquitous in today's electronic world. 00:00:15.766 --> 00:00:19.436 align:center line:-1 position:50% size:35% The one that you may be most familiar with is USB. 00:00:19.436 --> 00:00:24.900 align:center line:-1 position:50% size:56% To pass data and control information from one device or subsystem to another, 00:00:24.900 --> 00:00:30.239 align:center line:-1 position:50% size:49% signals in the form of digital bits are transmitted and received serially. 00:00:30.239 --> 00:00:34.409 align:center line:-1 position:50% size:39% That means one bit at a time, sequentially. 00:00:34.409 --> 00:00:37.412 align:center line:-1 position:50% size:29% High-speed systems, including many PCs, 00:00:37.412 --> 00:00:41.083 align:center line:-1 position:50% size:35% can transmit and receive billions of bits per second. 00:00:41.083 --> 00:00:44.336 align:center line:-1 position:50% size:46% There are many different protocols which you can think of 00:00:44.336 --> 00:00:46.672 align:center line:-1 position:50% size:29% as the data structure. 00:00:46.672 --> 00:00:49.800 align:center line:-1 position:50% size:31% Are bits transmitted most-significant bit first 00:00:49.800 --> 00:00:52.803 align:center line:-1 position:50% size:36% or least-significant bit first? 00:00:52.803 --> 00:00:54.596 align:center line:-1 position:50% size:36% How are the bits grouped? 00:00:54.596 --> 00:00:56.265 align:center line:-1 position:50% size:32% How are they encoded? 00:00:56.265 --> 00:00:59.768 align:center line:-1 position:50% size:35% How fast are bits transmitted and received? 00:00:59.768 --> 00:01:02.521 align:center line:-1 position:50% size:35% You can think of it as an agreed-upon language 00:01:02.521 --> 00:01:05.941 align:center line:-1 position:50% size:32% between two or more interconnected devices. 00:01:05.941 --> 00:01:07.943 align:center line:-1 position:50% size:41% If you speak to me in Chinese, 00:01:07.943 --> 00:01:11.029 align:center line:-1 position:50% size:37% I'm not going to understand too much beyond "ni hao," 00:01:11.029 --> 00:01:13.824 align:center line:-1 position:50% size:45% because I have English receivers. 00:01:13.824 --> 00:01:16.243 align:center line:-1 position:50% size:38% The most common protocols that you may encounter 00:01:16.243 --> 00:01:18.495 align:center line:-1 position:50% size:37% while studying engineering, 00:01:18.495 --> 00:01:21.206 align:center line:-1 position:50% size:53% especially during your capstone project, 00:01:21.206 --> 00:01:25.502 align:center line:-1 position:50% size:33% are I²C, which stands for inter-integrated circuit, 00:01:25.502 --> 00:01:29.548 align:center line:-1 position:50% size:34% SPI, which stands for serial peripheral interface 00:01:29.548 --> 00:01:32.092 align:center line:-1 position:50% size:49% and is sometimes pronounced "spy," 00:01:32.092 --> 00:01:37.597 align:center line:-1 position:50% size:47% UART, which stands for universal asynchronous receiver-transmitter, 00:01:37.597 --> 00:01:41.685 align:center line:-1 position:50% size:36% and CAN, which stands for controller area network. 00:01:41.685 --> 00:01:47.733 align:center line:-1 position:50% size:57% Hi, I'm Johnnie Hancock, Product Manager for Keysight's InfiniiVision oscilloscopes. 00:01:47.733 --> 00:01:51.862 align:center line:-1 position:50% size:44% In this lesson, we only have time to do a brief overview 00:01:51.862 --> 00:01:54.448 align:center line:-1 position:50% size:40% of just one of these protocols, 00:01:54.448 --> 00:01:59.703 align:center line:-1 position:50% size:50% but the basic concept of transmitting and receiving serial data is the same, 00:01:59.703 --> 00:02:02.664 align:center line:-1 position:50% size:46% regardless of the specific protocol. 00:02:02.664 --> 00:02:06.710 align:center line:-1 position:50% size:41% We'll be looking at an example of the CAN bus protocol. 00:02:06.710 --> 00:02:09.421 align:center line:-1 position:50% size:40% CAN is used in a broad range of applications, 00:02:09.421 --> 00:02:12.758 align:center line:-1 position:50% size:54% including control of industrial equipment, 00:02:12.758 --> 00:02:14.676 align:center line:-1 position:50% size:33% automotive applications, 00:02:14.676 --> 00:02:17.429 align:center line:-1 position:50% size:38% and robotics, which is where you may use this bus 00:02:17.429 --> 00:02:19.389 align:center line:-1 position:50% size:37% while in engineering school. 00:02:19.389 --> 00:02:23.268 align:center line:-1 position:50% size:43% Let's get started and take a look at some CAN electrical signals 00:02:23.268 --> 00:02:24.603 align:center line:-1 position:50% size:26% on an oscilloscope. 00:02:26.063 --> 00:02:27.939 align:center line:-1 position:50% size:34% This is a CAN bus signal. 00:02:27.939 --> 00:02:31.693 align:center line:-1 position:50% size:46% It happens to be one of the built-in education training signals 00:02:31.693 --> 00:02:34.112 align:center line:-1 position:50% size:27% of this oscilloscope. 00:02:34.112 --> 00:02:36.865 align:center line:-1 position:50% size:45% The CAN bus is a differential bus, 00:02:36.865 --> 00:02:38.658 align:center line:-1 position:50% size:41% should use a differential probe. 00:02:38.658 --> 00:02:40.285 align:center line:-1 position:50% size:39% It's differential because often, 00:02:40.285 --> 00:02:44.373 align:center line:-1 position:50% size:45% the signals have to be transmitted over a long distance 00:02:44.373 --> 00:02:48.710 align:center line:-1 position:50% size:34% and the differential bus is better for noise immunity. 00:02:48.710 --> 00:02:52.547 align:center line:-1 position:50% size:52% Let's go ahead and set up the scope and take a closer look at these signals. 00:02:52.547 --> 00:02:56.927 align:center line:-1 position:50% size:40% You set the scope up, initially, just like we've done before. 00:02:56.927 --> 00:02:59.554 align:center line:-1 position:50% size:43% I'm going to rescale the vertical. 00:03:03.475 --> 00:03:05.769 align:center line:-1 position:50% size:34% Now, set the trigger level. 00:03:05.769 --> 00:03:08.438 align:center line:-1 position:50% size:53% Set it about the center of the waveform. 00:03:08.438 --> 00:03:10.565 align:center line:-1 position:50% size:31% Rescale the horizontal. 00:03:10.565 --> 00:03:17.197 align:center line:-1 position:50% size:42% The first thing you notice is that all this digital information 00:03:17.197 --> 00:03:21.284 align:center line:-1 position:50% size:46% is coming out in bursts or packets. 00:03:21.284 --> 00:03:25.038 align:center line:-1 position:50% size:30% In CAN vernacular, they call them frames. 00:03:25.038 --> 00:03:29.459 align:center line:-1 position:50% size:31% Each of these bursts is a frame of information, 00:03:29.459 --> 00:03:31.002 align:center line:-1 position:50% size:20% or a message. 00:03:31.002 --> 00:03:34.381 align:center line:-1 position:50% size:23% Let's press Stop. 00:03:34.381 --> 00:03:38.427 align:center line:-1 position:50% size:37% Now, let's take a closer look at one of these packets 00:03:38.427 --> 00:03:40.345 align:center line:-1 position:50% size:31% or one of these frames. 00:03:40.345 --> 00:03:46.435 align:center line:-1 position:50% size:32% This particular CAN bus is running at 125 Kbps. 00:03:46.435 --> 00:03:48.770 align:center line:-1 position:50% size:49% Some people call that the baud rate. 00:03:48.770 --> 00:03:53.150 align:center line:-1 position:50% size:55% The CAN bus itself can run up to 1 Mbps. 00:03:53.150 --> 00:03:57.612 align:center line:-1 position:50% size:36% I'm going to zoom in on this particular packet here. 00:03:57.612 --> 00:04:01.950 align:center line:-1 position:50% size:39% I'm going to set the timebase or the horizontal 00:04:01.950 --> 00:04:06.872 align:center line:-1 position:50% size:38% at exactly 16 μs per division. 00:04:06.872 --> 00:04:10.375 align:center line:-1 position:50% size:31% The reason I set it at 16 μs per division is, 00:04:10.375 --> 00:04:16.465 align:center line:-1 position:50% size:44% 125 Kbps means each bit is 8 μs. 00:04:16.465 --> 00:04:24.306 align:center line:-1 position:50% size:36% Now, at 16 μs, I've set it up for each division to be 2 b, 00:04:24.306 --> 00:04:26.099 align:center line:-1 position:50% size:30% because what I want to show you right now 00:04:26.099 --> 00:04:31.062 align:center line:-1 position:50% size:40% is how many engineers would decode something like this 00:04:31.062 --> 00:04:32.355 align:center line:-1 position:50% size:23% many years ago, 00:04:32.355 --> 00:04:36.193 align:center line:-1 position:50% size:42% before automatic decoding was available on oscilloscopes. 00:04:36.193 --> 00:04:40.614 align:center line:-1 position:50% size:41% I call it the brute-force method. 00:04:40.614 --> 00:04:44.201 align:center line:-1 position:50% size:44% This is the beginning of a packet. 00:04:44.201 --> 00:04:58.423 align:center line:-1 position:50% size:55% Remember, each division is 2 b, so we have a 00 00 1 0 1111 01 000 100. 00:04:58.423 --> 00:05:02.719 align:center line:-1 position:50% size:36% Then, I'd have to slide over and do the next set of bits 00:05:02.719 --> 00:05:05.222 align:center line:-1 position:50% size:29% and slide over and do the next set of bits. 00:05:05.222 --> 00:05:11.728 align:center line:-1 position:50% size:40% This is a very painful process to decode this into 1s and 0s. 00:05:11.728 --> 00:05:14.356 align:center line:-1 position:50% size:44% Let's have the scope do it for us. 00:05:14.356 --> 00:05:16.608 align:center line:-1 position:50% size:39% I'm going to press Run again. 00:05:16.608 --> 00:05:22.405 align:center line:-1 position:50% size:41% Let's get one frame on screen. 00:05:22.405 --> 00:05:25.033 align:center line:-1 position:50% size:36% Some scopes have a button on the front panel. 00:05:25.033 --> 00:05:26.618 align:center line:-1 position:50% size:23% It might say Bus. 00:05:26.618 --> 00:05:28.703 align:center line:-1 position:50% size:25% It might say Serial. 00:05:28.703 --> 00:05:31.498 align:center line:-1 position:50% size:33% On this one, it's in the Analyze menu, 00:05:31.498 --> 00:05:34.668 align:center line:-1 position:50% size:27% so I'll select Analyze, 00:05:34.668 --> 00:05:39.172 align:center line:-1 position:50% size:32% and then turn on Serial. 00:05:39.172 --> 00:05:45.220 align:center line:-1 position:50% size:50% Next, I have to select the serial mode or the serial protocol. 00:05:45.220 --> 00:05:51.560 align:center line:-1 position:50% size:28% This scope supports I²C, LIN, SPI, UART, 00:05:51.560 --> 00:05:53.853 align:center line:-1 position:50% size:52% and the one up here at the top is CAN. 00:05:53.853 --> 00:05:55.647 align:center line:-1 position:50% size:34% This is a CAN bus signal. 00:05:55.647 --> 00:05:58.650 align:center line:-1 position:50% size:38% I have to tell the scope what language we're talking, 00:05:58.650 --> 00:06:00.026 align:center line:-1 position:50% size:21% which protocol. 00:06:00.026 --> 00:06:02.445 align:center line:-1 position:50% size:28% This is the CAN bus. 00:06:02.445 --> 00:06:10.537 align:center line:-1 position:50% size:58% Now you can see, below the signal, it is automatically decoding this frame here, 00:06:10.537 --> 00:06:15.250 align:center line:-1 position:50% size:46% or these frames that are occurring over and over hexadecimally, 00:06:15.250 --> 00:06:18.295 align:center line:-1 position:50% size:44% but it's jumping all over the place, and we can't see it. 00:06:18.295 --> 00:06:22.257 align:center line:-1 position:50% size:43% I could stop it and you could see the decode there. 00:06:22.257 --> 00:06:26.261 align:center line:-1 position:50% size:40% Do a single shot, another frame, another frame. 00:06:26.261 --> 00:06:28.972 align:center line:-1 position:50% size:34% The problem is, why is it jumping around like that? 00:06:28.972 --> 00:06:33.101 align:center line:-1 position:50% size:43% It's because we're not triggering on anything specific yet. 00:06:33.101 --> 00:06:36.646 align:center line:-1 position:50% size:36% The scope is still triggering on its default trigger mode, 00:06:36.646 --> 00:06:39.858 align:center line:-1 position:50% size:42% which is any edge of the signal. 00:06:39.858 --> 00:06:43.903 align:center line:-1 position:50% size:37% We can have it trigger on something specific to CAN. 00:06:43.903 --> 00:06:48.199 align:center line:-1 position:50% size:50% I'm going to go into the Trigger menu, 00:06:48.199 --> 00:06:50.660 align:center line:-1 position:50% size:27% select Trigger Type. 00:06:50.660 --> 00:06:54.331 align:center line:-1 position:50% size:35% You can see it says Edge. 00:06:54.331 --> 00:06:57.542 align:center line:-1 position:50% size:38% We talked about some of these other trigger modes 00:06:57.542 --> 00:06:59.544 align:center line:-1 position:50% size:24% in the last lesson. 00:06:59.544 --> 00:07:01.546 align:center line:-1 position:50% size:30% Let's go down here and select the bottom. 00:07:01.546 --> 00:07:04.883 align:center line:-1 position:50% size:26% It says Serial CAN. 00:07:04.883 --> 00:07:08.928 align:center line:-1 position:50% size:36% Now, it's locked in on what's called start of frame 00:07:08.928 --> 00:07:12.849 align:center line:-1 position:50% size:29% or start of any packet. 00:07:12.849 --> 00:07:17.145 align:center line:-1 position:50% size:40% There are other specific conditions you can trigger on. 00:07:17.145 --> 00:07:21.358 align:center line:-1 position:50% size:40% You'll probably have to do some homework and studying 00:07:21.358 --> 00:07:25.487 align:center line:-1 position:50% size:44% to fully understand the CAN bus. 00:07:25.487 --> 00:07:29.866 align:center line:-1 position:50% size:36% The one I'm going to select is Data Frame ID. 00:07:29.866 --> 00:07:32.077 align:center line:-1 position:50% size:26% It's like an address. 00:07:32.077 --> 00:07:38.583 align:center line:-1 position:50% size:38% Then, I'm going to say trigger on a specific address, 00:07:38.583 --> 00:07:41.378 align:center line:-1 position:50% size:39% and right now, it's triggering-- 00:07:41.378 --> 00:07:44.923 align:center line:-1 position:50% size:34% and it's not address, it's called ID or identifier-- 00:07:44.923 --> 00:07:52.305 align:center line:-1 position:50% size:54% it's triggering on the hex identifier of 000. 00:07:52.305 --> 00:07:55.058 align:center line:-1 position:50% size:35% The CAN bus, as well as other protocols, 00:07:55.058 --> 00:07:57.477 align:center line:-1 position:50% size:43% breaks everything up into fields. 00:07:57.477 --> 00:08:02.691 align:center line:-1 position:50% size:36% The first field, the first 11 b, is called the identifier field. 00:08:02.691 --> 00:08:05.276 align:center line:-1 position:50% size:36% That's where we have 000. 00:08:05.276 --> 00:08:08.988 align:center line:-1 position:50% size:40% The next field is a status field. 00:08:08.988 --> 00:08:13.952 align:center line:-1 position:50% size:40% Right now, it tells us DLC = 4. 00:08:13.952 --> 00:08:17.789 align:center line:-1 position:50% size:43% That's an indicator of how many data bits are going to follow. 00:08:17.789 --> 00:08:24.295 align:center line:-1 position:50% size:53% That is the body of this packet or frame, the data bits. 00:08:24.295 --> 00:08:29.259 align:center line:-1 position:50% size:33% To give you an idea, what do these fields do? 00:08:29.259 --> 00:08:31.094 align:center line:-1 position:50% size:31% The identifier might be, 00:08:31.094 --> 00:08:36.766 align:center line:-1 position:50% size:37% if you had a robotics project in your capstone project, 00:08:36.766 --> 00:08:44.274 align:center line:-1 position:50% size:44% and maybe one particular arm of your robot or robotics machine 00:08:44.274 --> 00:08:49.404 align:center line:-1 position:50% size:33% had an ID, might be 000. 00:08:49.404 --> 00:08:52.615 align:center line:-1 position:50% size:29% The data fields, these four data bytes, 00:08:52.615 --> 00:08:54.743 align:center line:-1 position:50% size:31% right now, I press Stop. 00:08:54.743 --> 00:09:00.373 align:center line:-1 position:50% size:31% It says 35, 4D, 3C, 85. 00:09:00.373 --> 00:09:03.710 align:center line:-1 position:50% size:40% That's four bytes, those are hexadecimal codes. 00:09:03.710 --> 00:09:11.718 align:center line:-1 position:50% size:50% Those four bytes might indicate an X, or an X, a Y, and a Z position 00:09:11.718 --> 00:09:15.180 align:center line:-1 position:50% size:28% of your robotics arm. 00:09:15.180 --> 00:09:18.600 align:center line:-1 position:50% size:49% Let's go ahead and press Run again. 00:09:18.600 --> 00:09:21.311 align:center line:-1 position:50% size:37% A different ID might position some other-- 00:09:21.311 --> 00:09:23.521 align:center line:-1 position:50% size:38% I don't know how many arms your robot has, 00:09:23.521 --> 00:09:27.901 align:center line:-1 position:50% size:49% but it might do a different positioning of your robotics arm. 00:09:27.901 --> 00:09:33.448 align:center line:-1 position:50% size:57% Let's get more of these packets on screen. 00:09:33.448 --> 00:09:35.867 align:center line:-1 position:50% size:44% As I get more packets on screen, 00:09:35.867 --> 00:09:41.956 align:center line:-1 position:50% size:52% you can see the decoded field below each of these packets or frames 00:09:41.956 --> 00:09:45.043 align:center line:-1 position:50% size:34% got squished, we can't read it anymore. 00:09:45.043 --> 00:09:47.420 align:center line:-1 position:50% size:53% There's another method of reading this. 00:09:47.420 --> 00:09:51.716 align:center line:-1 position:50% size:44% If I go back into the Serial menu, select Lister, 00:09:51.716 --> 00:09:54.552 align:center line:-1 position:50% size:45% now we can see a tabular format, 00:09:54.552 --> 00:09:58.515 align:center line:-1 position:50% size:32% and it shows us what each of these frames is 00:09:58.515 --> 00:10:00.517 align:center line:-1 position:50% size:29% on a line in this table. 00:10:00.517 --> 00:10:01.976 align:center line:-1 position:50% size:37% One thing you might notice. 00:10:01.976 --> 00:10:04.437 align:center line:-1 position:50% size:47% See this red floating through here? 00:10:04.437 --> 00:10:08.233 align:center line:-1 position:50% size:38% What's happening is the scope is detecting errors 00:10:08.233 --> 00:10:10.693 align:center line:-1 position:50% size:29% on this particular bus. 00:10:10.693 --> 00:10:14.113 align:center line:-1 position:50% size:37% We could set the scope up to trigger on specific errors. 00:10:14.113 --> 00:10:16.157 align:center line:-1 position:50% size:48% We're not going to do that right now. 00:10:16.157 --> 00:10:19.327 align:center line:-1 position:50% size:35% But we can see, things aren't working right. 00:10:19.327 --> 00:10:22.497 align:center line:-1 position:50% size:36% Perhaps your robotics arm is not positioning 00:10:22.497 --> 00:10:24.958 align:center line:-1 position:50% size:54% where you think it should be positioning. 00:10:24.958 --> 00:10:26.584 align:center line:-1 position:50% size:35% What is the cause of that? 00:10:26.584 --> 00:10:28.878 align:center line:-1 position:50% size:50% Maybe you programmed it incorrectly. 00:10:28.878 --> 00:10:32.549 align:center line:-1 position:50% size:43% That data field, maybe that was the wrong data. 00:10:32.549 --> 00:10:35.343 align:center line:-1 position:50% size:34% You need to go back in and correct the software. 00:10:35.343 --> 00:10:41.683 align:center line:-1 position:50% size:46% Or perhaps this error is picking up a signal integrity problem 00:10:41.683 --> 00:10:43.893 align:center line:-1 position:50% size:43% with the actual electrical signals. 00:10:43.893 --> 00:10:46.437 align:center line:-1 position:50% size:56% Maybe there's too much noise on the bus. 00:10:46.437 --> 00:10:49.315 align:center line:-1 position:50% size:29% We can see that with the oscilloscope. 00:10:49.315 --> 00:10:53.945 align:center line:-1 position:50% size:34% Perhaps some of the bits slid into the next bit field. 00:10:53.945 --> 00:10:56.364 align:center line:-1 position:50% size:42% The timing of the bits isn't right. 00:10:56.364 --> 00:10:58.074 align:center line:-1 position:50% size:35% Again, you could see that. 00:10:58.074 --> 00:11:01.703 align:center line:-1 position:50% size:48% You could also connect up another channel of the oscilloscope 00:11:01.703 --> 00:11:05.123 align:center line:-1 position:50% size:34% and maybe probe the actual analog signals 00:11:05.123 --> 00:11:09.168 align:center line:-1 position:50% size:42% that are moving the robotic arm and get a time correlation. 00:11:09.168 --> 00:11:13.464 align:center line:-1 position:50% size:43% When you send a command out to reposition a robotic arm, 00:11:13.464 --> 00:11:18.469 align:center line:-1 position:50% size:40% you can see the analog signal of the repositioning. 00:11:18.469 --> 00:11:19.721 align:center line:-1 position:50% size:25% During this lesson, 00:11:19.721 --> 00:11:22.932 align:center line:-1 position:50% size:41% I tried to give you a rough idea of what a serial bus is 00:11:22.932 --> 00:11:26.686 align:center line:-1 position:50% size:30% and how to decode it using an oscilloscope. 00:11:26.686 --> 00:11:30.815 align:center line:-1 position:50% size:45% Unfortunately, we didn't have time to cover this topic in detail. 00:11:30.815 --> 00:11:35.695 align:center line:-1 position:50% size:45% In our next lesson, we'll be talking about Lissajous curves. 00:11:35.695 --> 00:11:41.034 align:center line:-1 position:50% size:55% Remember: You can download additional technical information about oscilloscopes 00:11:41.034 --> 00:11:44.120 align:center line:-1 position:50% size:44% at the URL listed on your screen. 00:11:44.120 --> 00:11:46.456 align:center line:-1 position:50% size:32% Go, Cal Poly Mustangs!