Name: Diode Matrix - Finish and Test (2/2) @weirdboyjim
Uploaded: 2026-09-19T08:17:00-05:00
Duration: 8 min 17 s
Description: Diode Matrix - Finish and Test (2/2)

Diode Matrix - Finish and Test (2/2)

James Sharman 2026-09-19 | Diode Matrix - Finish and Test (2/2)

Tile Data PCB - VGA from Scratch - Part 14

James Sharman 2023-05-17 | I’m jumping forwards a bit and constructing the PCB for the circuit we designed in the last vga video. It makes more sense at this stage to do the pcb conversion in order of signal generation. Since most of the circuit design work is just reproducing the circuit we built in the previous video I totally understand that some people will want to use the contents to skip to the layout, soldering or installation sections.

0:00 Introduction
0:41 Build Explore and Check
2:48 Circuit EDA and Layout
7:26 Circuit Routing
16:15 Test PCB
17:14 Unboxing
18:37 Component Placing
19:51 Reflow
20:53 Hand Soldering
24:38 Install
27:17 Test
27:53 Demos
28:52 Outro

Analogue In - IO from Scratch - Part 2

James Sharman 2023-04-21 | I have joked in the past that I prefer to stay as far away from analogue signals as I can, but sometimes we want to deal with the real world. In this video I continue my new series on interfacing to look at reading in an analogue signal. Here we use a technique common in early gaming systems using general IO lines and a 555 timer in monostable configuration to read potentiometers. I finish of fully implementing a PC analogue joystick into the build with only a few basic components.

0:00 Introduction
1:19 Start with a potentiometer
2:37 555!
4:01 Principle test
5:05 the bit where I Turning my homebrew cpu into a basic clock circuit
6:33 First Test and troubleshoot
8:12 Creating a reading
9:34 Working Analogue Input
10:57 Connecting a Joystick
12:43 Reading both axis
15:45 Both axis working
17:02 Connecting the buttons
17:19 Fully working joystick!
17:54 Outro

EEVblog’s video on “How an Analog PC Joystick Works” youtu.be/hMBbnWjbUAU
Making the Joystick-Dupont adapter youtu.be/YcCYVFSQkg8

Adding GPIO - IO from Scratch - Part 1

James Sharman 2023-04-08 | In this video I add some simple GPIO lines to my homebrew cpu.

This circuit is extremely simple compared to some of the projects we’ve interfaced to the CPU but I want to interface a few components by what is colloquially called “bit banging” and to do that I need some general purpose I/O lines. This is really a reminder of how simple things can be but it also means I can move on and interface some circuits in future videos without the distraction of the cpu interface.

0:00 Introduction
0:32 Interfaces so far
2:51 Build
3:25 Build - Output
4:26 Build - Input
7:17 Stand alone test
9:33 Extra breakout
11:03 Integration
11:20 Adding software support
15:17 First testing
16:37 Test program
19:16 Outro

Tile Data - VGA from Scratch - Part 13

James Sharman 2023-03-20 | In this video I build one of the remaining modules for the vga. Tile data let’s us increase the effective resolution from 80x60 to 640x480 at the cost of a little flexibility. This build was not without it’s problems, I ran into a few issues mostly surrounding the difficulties of making a stable 25mhz circuit on a breadboard.

0:00 Introduction
0:48 Discussion
6:51 Build Explore and Check
12:01 Empty Breadboards
15:48 Wiring the ram chip
20:16 Tile Index Timing
21:55 Read address Inputs
26:20 Output Multiplexer
30:10 Write address Inputs
34:22 Stand Alone Testing
38:32 Integration
39:37 Adding an Output Latch
40:59 Turn it on!
45:35 Swap the Latches
46:05 Text Mode
49:18 Nibble Address Error
50:40 Demo: Fibonacci
51:27 Demo: Vga Terminal and Logo
52:25 Demo: Maze
53:48 Demo: Graphical Tile set
54:26 Demo: Monitor extensions for tiledata
55:15 Demo: Kodak Parrots
57:39 Extra Decoupling
58:32 Demo: Parallax Maze
59:42 Outro

Fixing the last Palette glitches - youtu.be/auarSG2MzdA

Backplane Troubleshooting - Making an 8 Bit pipelined CPU - Part 103

James Sharman 2023-02-15 | I didn’t like leaving the last video with a broken build. In this video I finish the process of find the fault and explore a number of different ways that problems can be patched.

0:00 Introduction
0:31 Troubleshooting
4:19 My Most Expensive Mistake Yet!
5:35 Breadboard Patch
9:21 Bodge Assessment
10:15 Rom Patch
14:01 Design Fix
17:58 Adapter Board Design
19:35 Adapter Soldering
23:29 Adapter Test
25:08 Outro
25:45 Post Credits Testing

Sections of the console output in the early part of this video didn’t record, I did my best to reproduce them for continuity.

New CPU Backplane - Making an 8 Bit pipelined CPU - Part 102

James Sharman 2023-01-31 | With parts of the build nearing completion I need to think about the final construction. I define an interconnection BUS and merge the core cpu components onto a single backplane. To get a board designed I also need to finalise the name of the build, something I’ve been putting of for far too long! There are a few teething problems so this will be followed by a troubleshooting video where I’ll hopefully get it working again.

0:00 Introduction
0:25 Name Reveal
0:53 Discussion
2:23 Backplane Layout
3:35 Expansion Connector
7:02 Backplane Design
10:26 PCB Routing
11:27 Unboxing
12:48 SMD Soldering
15:31 Module Headers soldering
22:38 Connector’s and Power components Soldering
24:47 Basic Tests
27:28 Peripheral Move
29:07 Module Transfer
32:55 Broken Pin fix
35:27 First Power On
37:20 Investigation
41:10 Outro

ZX Spectrum, Rom Cartridge Research

James Sharman 2023-01-11 | I continue to reminisce about my first computer by start to explore the expansion facilities. In this video I look at the subset of expansion port lines exposed through the rom cartridge port added by the interface 2. I build a breakout board and use it to interface a game rom image into the spectrum .

0:00 Introduction
0:38 Discussion
2:15 PCB Design
7:53 Unbox and solder
10:08 Testing
16:16 Troubleshooting
17:30 Success!
19:03 Future Plans
21:09 Outro
22:00 Post credits scene

Finding the Critical Path - Making an 8 Bit pipelined CPU - Part 101

James Sharman 2022-12-29 | In this video I analyse the cpu and attempt to identify the critical path through the circuit which constrains the clock rate. This was a thoroughly interesting experience which uncovered a few unexpected things but mostly confirmed the circuits workings.

0:00 Introduction
0:36 Discussion
2:16 Get the scope out!
3:39 ALU Inputs
9:03 ALU Output
11:42 Flags
14:28 Pipeline
17:28 Fetch
23:03 Conclusions
24:58 The Critical Path
27:18 Outro

Palette Play - VGA from Scratch - Part 12

James Sharman 2022-11-18 | Firstly I make good on my promise to explain the workings of the vortex demo I showcased in the last video. I also show a simpler plasma fractal demo as an example of normal palette cycling.

There was lots of discussion in the comments and on discord about what use we could make of the unused sections of the ram chips. In this video I explore a very simple circuit extension for doing that.

There is a brief bit of coding during the troubleshooting where I forgot to adjust the font size, apologies to anyone on a small screen.

0:00 Introduction
0:39 Vortex Demo Explanation
4:31 Plasma Palette cycle
5:41 Extending the Palette Hardware
10:16 Test
11:20 Image Fade Demo
12:26 Line Fade Demo
13:14 Shaded Cylinder Fail
14:14 Troubleshooting
17:19 Fixed!
17:51 Outro

Palette - VGA from Scratch - Part 11

James Sharman 2022-10-08 | In this video I design and build the circuit to add a Palette to my VGA circuit, together with the DAC’s from the last video forming what in modern terminology would be called a RAMDAC.

This video ended up being much longer than I like main channel videos to be. I can’t really cut a video a video like this down the middle as I like to bring chunk of work to a conclusion. I will try to break work chunks down a bit more in future to avoid big ones like this. It was several videos worth of work at all stages.

There is no Schematic inset for this video, I did record it but I couldn’t get it to fit onto the screen without obscuring important work or scaling it to the point of uselessness. I may release a rough cut on the extras channel or add it to the pcb design when I get to it.

0:00 Introduction
0:35 Demo of Current DAC’s
1:39 Design discussion
6:25 Exploring current setup
8:42 Build – Layout and Initial wiring
13:52 Build – Data Lines
18:04 Build – Address Lines
24:48 Build – Control Logic
33:35 Integrate
35:56 Test & Troubleshooting
40:42 Palette Parrot Demo
42:15 Palette cycle Mandlebrot Demo
43:15 Beam raced Palette change Demo
44:35 Normal Map Demo
46:31 Vortex Demo
47:15 Outro

The normal map demonstraited in this video is derived from Julian Herzog’s example on wikimedia commons.wikimedia.org/wiki/File:Normal_map_example_-_Map.png

Will it Run Doom? - Making an 8 Bit pipelined CPU

James Sharman 2022-08-09 | I get asked this question regularly so it was about time I did a video to address the answer directly. This video is a platform to introduce my new demo “doomed” that I’ve written for the system that is as far along the path to a Doom like 3d engine as I expect to get on this little 8-bit device.

0:00 Introduction
0:54 Doom?
1:17 Discussion
2:48 Doomed
3:34 Outro

Join us on Discord: discord.gg/jmf6M3z7XS
Support the channel on Patreon: patreon.com/JamesSharman
Watch the companion video “Programming Doomed” on my Extras channel: youtu.be/sC3Issh5cPQ
Get monthly updates from a variety of makers by signing up for the new MakerNews letter: makernews.substack.com

DAC Test - VGA from Scratch - Part 10

James Sharman 2022-07-26 | In the first vga video I set a goal of being able to reproduce “millions of colours” but at present my digital to analogue converters are either 3 or 2 bits per channel. I need at least 7 bits per channel to hit that goal, preferably 8. I had a plan but comments have called it into question, in this video I talk about my original plan, why it might be flawed and what the alternatives might be.

0:00 Introduction
1:04 Discussion
8:58 PCB Design
15:42 Unbox and Solder
19:37 Stand alone Test
26:54 Test Integration
29:41 Outro

Tilemap PCB (Fix!) - VGA from Scratch - Part 9.5

James Sharman 2022-07-09 | I really wanted to fix the tilemap pcb before I moved on, some of the future circuits are going to be based on it so a fully working circuit was a must. I start by resolving the bit order issue in the schematic and pcb, additionally I add some extra ground connections which are something that I think I need to pay more attention to.

I recently bought a soldering hot plate, this is the first full PCB using it.

Tilemap PCB - youtu.be/TpolGhGUe9Y
Hot Plate - youtu.be/nYzFj7fpsPI

0:00 Introduction
1:04 A Look at the problem
1:57 Fixing the design
6:16 Unboxing
7:22 Component Place
10:51 Epic new soldering plate!
11:55 Through hole soldering
13:05 Install and Test
14:14 troubleshoot and fix
17:03 Success!
18:05 Outro
18:49 The Frame of Shame!

SNES Controller Interface – Part 2 – Connecting to the homebrew CPU

James Sharman 2022-06-27 | The next big step for the SNES controller interface is to build the circuitry that allows connection to a CPU. I build the circuit on breadboard and connect it to my homebrew CPU. I briefly cover the code necessary to read from the controller and finish by adding support to my serial terminal game “Snek”.

0:00 Introduction
0:41 Circuit Recap
1:25 Discussion
4:19 Build
12:37 Integrate into CPU Build
13:26 Add Support
17:41 Testing
19:11 Snek!
21:28 Outro

Join the channels Discord: discord.gg/jmf6M3z7XS
You can support the channel on Patreon: patreon.com/JamesSharman

Tilemap (Framebuffer) PCB - VGA from Scratch - Part 9

James Sharman 2022-06-12 | I knew this pcb was a big job, just editing all this footage was several evenings work. The tilemap pcb is one of the more complex pcb’s in the build and an important one to get right. Having this work frees up a lot of space and some of it’s concepts will be important to moving quickly through the tile data, palette and sprite work.

This is converting the circuit built in the following videos
Framebuffer - youtu.be/_w5bc9CLDrk
Scrolling - youtu.be/oMGtJN1Pkis
Beam Racing - youtu.be/9crrf0WoAvU (A tweak to the scrolling)

0:00 Introduction
1:46 Extraction
2:56 Schematic design
17:52 PCB routing
34:14 Unboxing
35:07 Pick and Place
38:40 Soldering
40:44 Install & Test
41:38 Troubleshooting
43:25 Software Workaround?
46:20 Outro

ZX Spectrum+, UnBox, Test, Mod and Repair

James Sharman 2022-06-01 | The first computer I ever owned was a ZX Spectrum+ (This is the same circuit as the old rubber key model but with a better keyboard, ours was actually an upgrade from the rubber key version). I’ve got a few plans for a couple of videos checking out the signals and interfacing some logic to this, how much depth I go into will depend on the response. This was sold “as-seen” so I take a bit of care checking things before switching it on. Both the power connector and the output resistor in the modulator were loose, so this wouldn’t have worked (at least not reliably) but I fix those issues as well as modifying the output for composite video.

0:00 Introduction
0:31 Unboxing
3:53 Resoldering Power connector
5:55 Composite Mod
9:39 It’s alive
12:30 Testing the Keyboard
17:37 Outro

SNES Controller Interface – Part 1 – Reading the inputs

James Sharman 2022-05-29 | I want more buttons than the NES controller is going to give me, so I’m start a new mini-series to interface a SNES controller to my homebrew cpu. In this video I build the basics of a circuit to read the button status in. I’m expecting this to be a 3 part video series which will probably set a new record for me going from breadboard circuit to finished pcb.

0:00 Introduction
0:48 Starting the circuit
4:25 Get the scope out!
10:07 It’s Alive!
11:01 Outro

Links:
Snes Controller to Dupont Adapter youtu.be/ag582oYVmR4
DIY NES Controller - Full Build youtu.be/d_ztfv2ZM6k
Interfacing With a NES Gamepad youtu.be/bSWNnPtwb_g

Interface PCB - VGA from Scratch - Part 8

James Sharman 2022-05-20 | This is the 2nd VGA PCB and it’s really the “Below Decks” functionality. It buffers and decodes the signals from the main cpu. In this video I do make a stupid mistake, fortunately one I can rectify but a reminder to be careful.

0:00 Introduction
1:47 Schematic design
4:04 Memory Map
11:32 PCB Layout
12:14 PCB routing
17:17 Unboxing
18:17 Pick and Place
19:17 Soldering
21:38 Install & Test
28:54 Fix
29:48 Re-test
32:41 Outro

10,000 Subscriber Milestone!

James Sharman 2022-05-11 | Hit this one a bit sooner than I expected and felt it was worth marking the occasion! I spent a little downtime writing a small firework display merged in with a music player, a few people I know had been curious to see graphics and sound at the same time so this ticks that box as well. I strongly suspect this will be the last time I get to celebrate an extra digit on the counter!

Notes:
You don’t think about how long the coffee machine takes until you are editing it in a video!
Upward facing camera to a face illuminated from beneath with led’s is REALLY unflattering!

Is this the most powerful 8-bit system ever? - Making an 8 Bit pipelined CPU - Part 100

James Sharman 2022-05-03 | For the 100th video I thought I’d take some time to profile the system and compare it to the 8bit micros of my youth. I was greatly assisted by the “8-bit Battle Royale” over on Matt Heffernan’s channel and his publicly available code that I ported to the homebrew cpu.

0:00 Introduction
0:33 Build Tour
1:12 Benchmark discussion
3:08 It’s a Race!
4:43 Results Discussion
8:12 Capturing instructions per clock rate
14:31 Outro, is it the fastest?

Matt’s Channel: youtube.com/channel/UCWihlGXWuyJbjP5vjzD03Rw
8-Bit Battle Royale: youtube.com/playlist?list=PLPSrOWYluVLIwjHSJKuO8UU8BTT3uceqU

Porting Video on my Extras Channel: youtu.be/eBbtlLnYZ1A
chat about this and related projects on the discord: discord.gg/jmf6M3z7XS

Sync PCB - VGA from Scratch - Part 7

James Sharman 2022-04-22 | This is exciting! In this video I turn convert the sync generator circuit from breadboards to a pcb. This is the first of the vga modules to get finalized and really marks the start of the final phase of construction.

Backplane solder on 2nd channel: youtu.be/wfvLBACrB1E

Spring Cleaning - Making an 8 Bit pipelined CPU - Part 99

James Sharman 2022-04-13 | This video is about tidying up a few things in the build. A couple of the pcb’s had mistakes and needed bodge wires. I fixed the schematics at the time of the original soldering but it was about time I got around to testing them. I had reason to be suspicious that the logic backing some of the conditional jumps was not correct so I additionally wrote some code to test those exhaustively.

0:00 Introduction
1:00 Clock PCB v1.1
1:56 Clock test
4:26 Testing the conditionals
9:16 Fixing the conditionals
13:20 ALU Result PCB v1.1
14:47 ALU test
16:42 Outro

Clock PCB v1.1 youtu.be/Odl_o9POwL8
ALU Result PCB v1.1 youtu.be/ZqbilYwKAQo

New Controller - Audio from Scratch - Part 9

James Sharman 2022-04-01 | There have been a few changes to the circuit over the last couple of videos so here is where I bring it back together. I build a new controller that can drive all 4 channels we put on pcb. I modify the output to just use an op-amp as buffer and a DC blocking capacitor to clean the signal. This comes together really well and it’s good to finally see all 4 channels working as intended!

There is probably just a final PCB build video left in this sub series, and maybe some software work seeing what we can do with it.

0:00 Introduction
1:03 Discussion
2:15 Build
3:44 3 States
8:10 Latches
11:10 Register Select
14:25 Predictable initialisation
17:50 Connecting to Channels
21:00 New output circuit
24:25 Connecting to the CPU!
26:01 Initialisation Code
27:38 Fail!
28:48 More testing
29:48 Code tour
30:30 4 Channel Demo!
31:37 Outro

Bus Tester PCB – Full Design and Build

James Sharman 2022-03-25 | I’ve been slowly tweaking a bus testing circuit on breadboard but it’s become unwieldy and unreliable (mostly because it was made a cheap breadboard). In this video I finally get around to making a permanent version on PCB which will hopefully facilitate the rest of my cpu build.

0:00 Introduction
1:08 EasyEda design
14:03 PCB routing
19:39 Unboxing
21:05 Human pick and place
23:43 Hot Air reflow
28:27 Testing
29:16 Troubleshooting
32:04 Success!

Confession: The oscilloscope capture in the testing section is a “re-enactment” the original footage didn’t record.

Geiger–Müller counter Kit

James Sharman 2022-03-18 | I’ve wanted one of these for ages (I have project ideas using it as a module), driving it would involve a lot of experimentation with analogue electronics so I purchased a kit from Amazon.

Technically this isn’t a Geiger counter, it’s just the tube with the driver circuit but I have plans to turn it into a real counter so this will turn into part 1 if I actually get that far before being distracted.

0:00 Introduction
0:31 Unboxing the kit
2:28 Soldering
12:18 Testing
15:27 Outro and Plans

PCB Planning - VGA from Scratch - Part 6

James Sharman 2022-03-11 | I’ve been blocked on the vga circuit trying to work out how modules in the vga should fit together. This video is the “tip of the iceberg” in a big pcb order I’ve just put in that will move several sections of the build forward. Lots more videos are in progress.

0:00 Introduction
3:30 Guessing Size
8:09 Working out connectors
16:52 Temporary Backplane
18:43 Outro

The Sieve of Eratosthenes

James Sharman 2022-02-03 | The first big demo for my homebrew cpu generated prime numbers using a variant of the Sieve of Eratosthenes. Ever since then I’ve had a various comments and requests for more information about the algorithm. This video explains the Sieve and it’s variants with a leaning towards practical implementation, I do cover a few specifics about why I chose this for a first demo but it should serve as a good introduction to the algorithm on it’s own.

This video covers the Sieve, the Segmented Sieve and the Incremental Sieve.

The painting of Eratosthenes I’ve used is “Eratosthenes teaching in Alexandria by Bernardo Strozzi (1635)”

Synthesizer Channel PCB - Audio from Scratch - Part 8

James Sharman 2021-10-23 | This one feels a bit less exciting than the vga videos, but an important step towards the finished product. I explain this briefly in the video but there has been a big gap between audio videos because I was having a rethink on how some bits would work. Rather than use 4 latches from an 8-bit bus I’ve decided to switch towards 2 latches from a 16 bit bus (which will need work on a new control circuit to drive it).

Still, I wanted to make some solid progress so I designed those changes directly into the channel(s) pcb. I had originally hoped for four single channel pcb’s but it was easier to make a pair of pcb’s with two on each.

No music this time as we need to make some changes to the circuit driving it, but the next audio video should give us the first playback with all 4 channels.

0:00 Introduction
2:16 Eda circuit update
5:32 Layout attempt 1
7:21 Switch to 2 channel board
8:56 Layout double board
11:11 Routing
20:34 Backplane
20:54 Unboxing
21:30 Soldering
26:11 Backplane soldering
27:23 Testing
32:27 And Again!

Join me on the new channel discord server: discord.gg/jmf6M3z7XS

Beam Racing - VGA from Scratch - Part 5

James Sharman 2021-09-14 | This video is a little different, I introduce the concept of beam racing as a technique to do more interesting things with video hardware. This ended up being more of a show and tell with only a little bit of circuit building to make the functionality more suitable.

I wonder if watching this video will realign some peoples expectations for what a basic display circuit is capable of. I’ll revisit some these techniques and demos as we add new hardware to see how far we can take them.

0:00 Introduction
1:22 Demo: WibbleX
2:22 Demo: Pseudo Parallax
5:17 Tweaking the Circuit
7:58 Demo: WibbleY
9:05 Demo: Cylinder
10:35 Demo: Candle Flame
12:26 Demo: Race Track
13:58 Outro

Hardware Scrolling - VGA from Scratch - Part 4

James Sharman 2021-08-27 | Join me on the new channel discord server: discord.gg/jmf6M3z7XS

In the first three vga videos we built up the most basic stand alone video subsystem. At the end of the last video the freed up cpu time was put to use with our first animating graphics. Animation is where things start to get interesting and one of the most useful 8-bit era building blocks to that end is hardware scrolling. In this video we explore how to add this to the vga circuit.

0:00 Introduction
1:00 Counter initialization
2:38 More Breadboards
5:45 New Registers
10:20 Memory Mapped IO Discussion
15:54 IO Implementation
19:42 Initial Test Code
22:18 Smooth Scrolling!
24:18 Super wide scrolling! (Incremental update)
26:26 Vertical Scrolling
28:46 Main Demo
29:42 Boring James talking outro bit

Framebuffer - VGA from Scratch - Part 3

James Sharman 2021-08-01 | Join me on the new channel discord server: discord.gg/jmf6M3z7XS

In this video I add a framebuffer to the developing vga circuit. In many ways this makes the circuit a complete (if simple and low specification) vga adapter that we'll go on to add functionality too in future videos. Adding the framebuffer only increases the visual quality a little bit (The horizontal resolution is no longer limited by cpu clock rate) but it does free up the cpu.

To demonstrate this I write some decompressor code that could be called basic looped video or gif type animation playback and use it to play some recognisable animations on the cpu/vga combination.

0:00 Introduction
0:29 Re-cap
4:40 Adding X/Y Counters
10:45 Memory Interface discussion
11:34 (1) Duel Port Ram
13:31 (2) Time-Division Multiplexing
15:30 (3) Bus Request
18:20 (4) Hybrid
21:00 (4.1) Hybrid+
21:56 Adding the Ram
28:55 Interfacing
34:19 Back to the cpu
38:40 Pattern Test
40:57 Image test
42:38 Corruption!
43:50 Animation Test
45:30 Post credits scene

Turbo charging development, The Bootloader - Making an 8 Bit pipelined CPU - Part 98

James Sharman 2021-07-04 | Join me on the new channel discord server: discord.gg/jmf6M3z7XS

Now the UART is a reliable PCB it's worth the effort to develop a monitor/bootloader in order to streamline future development. I had been back and forth on exactly what I would develop, but I always wanted to introduce something to speed the process of getting code to the build. I start by showing a true accounting of the iteration time to get code to the build with the eeprom programmer, and then finish with some rapid testing using the new system.

0:00 Introduction
0:47 Tedious and boring, demonstrating the problem
3:00 Some soldering, speeding up the copy.
4:21 Testing improved copy speed
5:33 Starting a monitor, Text entry
7:19 Command parsing
8:23 Interpreting numbers
10:05 Command Processing
10:55 Basic monitor demonstration
12:37 Proof of concept code loading
14:19 Disassembler
16:09 Testing the disassembler
17:55 Better code loading
19:34 Stub loader, Moving the Monitor
24:16 Testing the Bootloader!
25:50 Outro

Sync - VGA from Scratch - Part 2

James Sharman 2021-06-16 | In the first VGA video the circuit required the CPU to do all the hard work generating both the sync and outputting the colour data. In this video we build circuitry to generate the sync signal and the free some of the CPU time up.

0:00 Introduction
0:54 Base Test
4:20 Discussion
8:51 Counters
10:52 Adding the ROM
13:45 Rom Data
16:10 Sync Test
18:34 New DAC's
22:16 Quick Hack Image
25:35 CPU Integration
27:47 Best Parrot Yet!
29:42 Animation!

Finished PCB? - UART from Scratch - Part 8

James Sharman 2021-06-10 | In the previous 7 videos in the Uart side project we have designed and built the circuit for a single speed Uart with receive and transmit fifos. In this video I transcribe the last section to pcb and put it all together.

The achievement is marred a little by an error on the silk screen. I'll decide if I'll do a new board revision or just print out a label to stick over it at a later point.

0:00 Introduction
1:14 Schematic
12:42 Layout
15:12 Routing
18:32 Unbox
21:55 Hot-Air
25:57 Test

Introduction - VGA from Scratch - Part 1

James Sharman 2021-05-29 | The start of a new side project to build a VGA display interface for my homebrew cpu. This will probably be the largest side project so I start with a discussion on my goals for the build and then go on to get the most basic possible version working to get things going.

0:00 Introduction
1:58 Project Goals
6:16 VGA signal
8:37 Build Process
10:47 Circuit build
14:36 Initial Programming (H-Sync)
17:39 H-sync Test
18:53 Video Code tour
20:54 Test

Mailbag #11 Core Bits

James Sharman 2021-05-24 | I had a small collection of parcels to open with one particular item that I really want to share with you so I thought I was overdue a mailbag video. As always, most of the items are likely to feature in future videos.

Pin headers - amzn.to/3hMfwyW
DB15 breakout - ebay.co.uk/itm/393273511221
LCD - ebay.co.uk/itm/313183790652
Core Memory - etsy.com/uk/listing/925863268

0:00 Introduction
0:06 Pin headers
0:51 VGA breakout
2:03 SPI Display
3:14 Oscilloscope Probes
4:48 MCP23017
5:20 Core Memory
8:11 Fin

Shadow Ram PCB - Making an 8 Bit pipelined CPU - Part 97

James Sharman 2021-05-15 | In Part 96 I Built and tested the shadow ram system on breadboard. In this video I finish of the schematic, order a PCB and solder it up.

0:00 Introduction
1:29 Finishing the Schematic
7:44 Layout
11:09 Routing
13:49 PCB Unbox
14:15 Stencil and Paste
15:40 Component Placement
19:48 Hot Air
22:48 Install and Test

Backing music for the time-lapse is "Active Form" by "Chasms" that they kindly provided to the youtube free music library.

Transmit FIFO - UART from Scratch - Part 7

James Sharman 2021-05-03 | Final bit of functionality to be added to the UART is hooking up the transmit FIFO. After getting that working I make the appropriate changes to the UART library necessary to interface it back into the CPU.

I've added a new microphone stand and this is the first time I used it for recording a video. The Quality is much improved (better signal to noise) but it is much more sensitive to me moving my head while wiring. I'll be more careful in future.

0:00 Introduction
1:37 Rewire
4:47 Build Transmit
17:06 Design Flaw?
19:35 Interface to CPU
20:39 Code
23:32 Test & Troubleshooting
25:36 Working

Design Retrospective - Making an 8 Bit pipelined CPU

James Sharman 2021-04-19 | I asked for some question and got a far bigger response than I expected. This is my longest video to date (it took an age to edit). I'm expecting most people to use the index to skip to answers they want to see rather than sit down and watch it like a feature.

0:00 Introduction
1:03 CPU Overview
11:57 What is the power consumption?
13:58 Pipeline - Basics
18:25 Pipeline - 4th Stage?
20:28 Pipeline - Performance
23:13 Why no Interrupts?
32:00 External Storage
33:38 Tool chain
35:13 What would I do differently?
46:12 What about floating point?
47:37 Is it a distraction?
48:41 Flag preservation
51:45 Will I add an RTC?
52:28 How much did it cost?
54:46 Additional Core?
56:03 All Teh features?
57:13 Stack Register?
59:33 More Peripherals?
59:52 Selling Boards?
1:00:59 What Clock Speed can it Run at?
1:03:59 Multibyte instructions?
1:06:12 Caching?
1:07:59 Has my soldering Improved?
1:09:00 Video Card?
1:10:16 Documentation about the build?
1:11:25 Detailed ISA?
1:12:25 Architecture Specification?
1:14:01 Fin.

Easyeda Profile: easyeda.com/weirdboyjim

Receive FIFO - UART from Scratch - Part 6

James Sharman 2021-04-04 | The fixed FIFO PCB's have arrived so in this video I solder 2 of them. You can probably guess what the next UART video will be, but Id dint' want to tackle

0:00 Introduction
1:35 PCB Unbox
2:56 Soldering Race
4:41 Test
7:28 Receive FIFO
13:24 Finish up

In the unboxing I found a random puzzle which I completed in a side box next to the soldering. I speed this up roughly 2x relative to the soldering to fit the gap, I don't want anyone to think I'm misrepresenting my puzzle solving.

Backing music for the soldering is "Active Form" by "Chasms" that they kindly provided to the youtube free music library.

Shadow Ram Copy - Making an 8 Bit pipelined CPU - Part 96

James Sharman 2021-03-25 | In Part 91 I described my plans for a shadow ram system that copies from a rom chip to ram to give me lots more memory flexibility. Behind the scenes I designed a small pcb to help prototype that, so in this video I solder that up and build the copy circuit.

0:00 Introduction
1:22 Schematic EDA
3:21 Unbox
4:45 Soldering
6:00 Test Code
9:14 Basic Counter
16:06 Memory Interfacing
25:09 Outro

Architecture Questions Request - Making an 8 Bit pipelined CPU

James Sharman 2021-03-23 | Now the cpu core is essentially complete and on PCB, I'd like to do a video soon as a kind of architecture retrospective. I've got a few things planned that I'd like to talk about but the comments here is an opportunity for you to ask any questions or make any comments about the cpu architecture. I'll try and answer everything in the retrospective video. Ask me anything (about the cpu core).

ALU Output PCB - Making an 8 Bit pipelined CPU - Part 95

James Sharman 2021-03-16 | This is a big milestone point, for the core of the cpu only one block of breadboards remains. In this video I convert the ALU output module to a PCB and get the first execution without any breadboards.

0:00 Introduction
2:29 Schematic
11:12 PCB Layout
20:51 PCB Unbox
21:11 Soldering
26:55 Test and Bughunt
33:10 Bodge Fix
41:17 Final Test

Output - Audio from Scratch - Part 7

James Sharman 2021-03-08 | I spend a little time improving the analogue output of the sound module. I'm not very comfortable with the analogue side things so this is me working things out as I go. It is the last thing I wanted to do before converting the sound module to a pcb though.

0:00 Introduction
0:17 R2R Ladder
5:46 Ground level
7:14 Op-Amp
9:15 -5v
13:54 Finish

Bitluni did a good video explaining R2R resister ladders - youtube.com/watch?v=_tABS7AX8D8

LCD PCB - Making an 8 Bit pipelined CPU - Part 94

James Sharman 2021-02-28 | I'm not planning on the LCD module making it to the final configuration of my build, but in many ways this video makes the LCD the first sub component to achieve "completed" status. I take the schematic work from Part 93 and design a PCB to drive the LCD. I also design and 3dprint a support.

0:00 Introduction
0:48 PCB Design
4:15 Soldering
9:22 Cad
13:22 Assemble
14:08 Finish and Test

I'm waiting on a delivery before I can complete the final module in the ALU but I wanted to do this anyway so we'll have a moment when the CPU is entirely PCB.

I have experienced some glitches on the enable line which I cleaned up with a low value (1nf) cap, I'll investigate this a bit more when I get some time and maybe report back.

FIFO PCB - UART from Scratch - Part 5

James Sharman 2021-02-21 | I want both a send a receive fifo buffer on my UART, rather than fill my desk with bread boards (again) I'm designing a module I can both use on the breadboard UART but also use as a plug in module on a future UART pcb.

0:00 Introduction
1:45 PCB Design
11:18 unbox and solder
17:10 Test
22:27 Schematic fix
23:29 Outro

LCD Improved - Making an 8 Bit pipelined CPU - Part 93

James Sharman 2021-02-14 | In video 55 I interfaced a "temporary display" in the form of an HD44780 module. That interface was limited to only write to the registers and such I had no access to the busy status bit that would be necessary to drive it at high speed. In this video I extend the circuit to add that functionality. This is still just a temporary display but this makes the functionality more complete and will allow it to be more useful for some speed tests I want to run when the core cpu is complete.

0:00 Introduction
2:01 Design Discussion
5:57 Build
13:33 Coding
16:24 Test & Troubleshooting
18:04 Circuit Fix
20:46 Coding
22:28 Finish and Test

In the second coding section I made a small mistake, I've edited out the short test run where I discovered that as it just didn't flow well in the edited video but if you watch very closely you can see the mistake and then the fix tagged on the end.

ALU Control PCB - Making an 8 Bit pipelined CPU - Part 92

James Sharman 2021-02-06 | In this video I convert the ALU control to PCB's, it doesn't really reduce the breadboard count since most of the work was done by a diode matrix pcb already. It does replace some circuitry on the remaining breadboards but I'd need to do a re-organisation to remove one.

If you want to understand the workings of this circuit, you should watch:

youtube.com/watch?v=LkM9tBCAros (Alu control)
youtube.com/watch?v=Slm3yZyVidc (Diode Matrix 1/2)
youtube.com/watch?v=UXz_rTgeAEc (Diode Matrix 2/2)

0:00 Introduction
1:14 EDA Design
18:33 Soldering
25:24 Install and Test

Notes: Since editing I've used the circuit a lot and not seen a repeat of the bad connection. I did however discover that resistor associated with the ADD led wasn't connected properly, I had to resolder that for the LED to work.

More Ram? - Making an 8 Bit pipelined CPU - Part 91

James Sharman 2021-01-30 | I've decided that some of my plans for the build would benefit from having more RAM. I originally made a 32K/32K RAM/ROM split but I'd like to introduce a shadow ram system so that running code has access to the whole 64k of ram. In this video I bodge in the extra 32k ram, test it and showcase some advancements I used in the tool chain.

This video is really the first in a sub series to upgrade the memory module to using shadow ram but I didn't want a big wait and then a massive video.

0:00 Introduction
0:54 Discussion
5:16 EDA
7:04 Bodge Soldering
14:31 Code
17:55 Install and Test

Logic Unit PCB - Making an 8 Bit pipelined CPU - Part 90

James Sharman 2021-01-22 | Logic Unit PCB - Making an 8 Bit pipelined CPU - Part 90

This is ALU pcb conversion 2/4, the bitwise logic unit. Very pleased with this PCB, for some reason it one was extra satisfying. The circuit I'm converting here was designed in part 34. youtu.be/pMV_0qT0uY0

0:00 Introduction
0:33 EDA
13:25 Solder
17:48 Install and Test