RS232 interface with the 6551 UART

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Special thanks to these supporters for making this video possible:
Adrien Friggeri, Aleksey Smolenchuk, Alex, An Dương, Anthony Weems, anula, Ben, Ben Cochran, Ben Williams, Bill Cooksey, Bill Watkins, Binh Tran, Богдан Федоров, Bradley Stach, Brian Haug, Burt Humburg, Carl Fooks, Carsten Schwender, Chai, Chris Anders, Chris Lajoie, Chris Sachs, criis, Cristi Cobzarenco, Daniel Jeppsson, Daniel Pink, Daniel Tang, Darrell Burgoon, Dave Walter, David Clark, David Cox, David Dawkins, David House, David Sastre Medina, David Turner, Dean Bevan, Dean Winger, Deep Kalra, Dennis Henderson, Dennis Schubert, Dilip Gowda, Dirk Sperling, Dmitry Guyvoronsky, Dušan Dželebdžić, Dustin Campbell, Dylan Speiser, Dzevad Trumic, Emilio Mendoza, Eric Dynowski, Erik Broeders, Erik Granlund, Ethan Sifferman, Eugene Bulkin, Evan Serrano, Evan Thayer, Eveli László, EvinSaysMarxWasRight!, Florian Bürgi, fxshlein, George Miroshnykov, ghostdunk, GusGold, Hailey, Hovis Biddle, Humberto Bruni, Ingo Eble, Ivan Esparza, Jacob Ford, James Beldock, James Capuder, Jared Dziedzic, Jason Bowen, Jason DeStefano, Jason Grim, Jason Thorpe, JavaXP, Jaxon Ketterman, jemmons, Jeremy Cole, Jesse Miller, Jim Kelly, Jim Knowler, Joe Beda, Joe Pregracke, Joe Rork, Joel Miller, Joey Murphy, John Hamberger jn., John Henning, John Meade, Jon Dugan, Jonn Miller, Joseph Portaro, Jurģis Brigmanis, Justin Graziani, Kai Wells, Kefen, Ken Paul, Kennard Smith, Kenneth Christensen, Kyle Kellogg, Lambda GPU Workstations, László Bácsi, Lithou, Lord Dorogoth, Lukasz Pacholik, Marcos Fujisawa, Marcus Classon, Mariano Uvalle, Mark Day, Martin Noble, Mats Fredriksson, Matt Krueger, Matthew Clifford, melvin2001, Michael Koreshkov, MICHAEL SLASS, Michael Tedder, Michael Timbrook, Michael Weitman, Miguel Ríos, mikebad, Mikel Lindsaar, Miles Macchiaroli, Muqeet Mujahid, NacOJerk, Nate Welch, Nicholas Counts, Nicholas Moresco, Nick Chapman, Oli Homer, Ori Shamir, Örn Arnarson, Paul Heller, Paul Pluzhnikov, Pete Dietl, Phil Dennis, Philip Hofstetter, ProgrammerDor, Ralph Irons, Randal Masutani, Randy True, raoulvp, real_huitz, ReJ aka Renaldas Zioma, Ric King, Rick Hennigan, Rob Bruno, Robert Diaz, Robert Keown, Robey Pointer, Roland Munsil, Sagnik Bhattacharya, Sam Sturgis, Scott Gorlick, Scott Holmes, Sean Bright, Sean Patrick O’Brien, Sergey Kruk, Shane Mulcahy, SonOfSofaman, Spencer Ruport, Stefan Nesinger, Stephen Kovalcik, Stephen Riley, Steve Jones, TheWebMachine, Thomas Eriksen, Tim Oriol, Tim Walkowski, Tim Wheeler, Tom, Tom Smith, Tyler Latham, Usseod, Vincent Bernat, Warren Miller, Wim Coekaerts, Yee Lam Wan

[MahBor]

It's a great day when Ben Eater uploads

[Jenny_Digital]

A word of caution regarding the W65C51S parts. There’s a horrific silicon bug where the transmit buffer empty bit is stuck. Earlier versions of the datasheet mention this but the current version tries to sugar coat this issue. Shame there’s nobody else (that I’m aware of) making this otherwise very very easy to use part.

[Q]

This 6502 project series is really taking me down memory lane! I got started with a Heathkit H8 that was completely hand soldered, this was around ‘78 and I was in 7th grade. Me & pops build it over a weekend. My school chums had an Apple II which ran at 1.5MHz and my 8086 based H8 ran at 2MHz. Oh the ribbing they got for their “slow computer!” Lol! I upgraded the H8 with a Z80 and software programmable clock speed of 2 or 3MHz. No video or hard drives, just a vt100 terminal and dual 100K hard sector floppies. Could choose CP/M, HDOS, or UCSD Fortran operating systems. Had to write all of my own software and had assembly, Basic, Fortran and C languages to choose from. Great memories, thanks Ben!

[erichobbs]

I really appreciate Ben's teaching style of showing the simple or nieve solution first, and then diving into the more efficient and reliable solution. You get an idea of how the thing can work at a basic level, before showing you the limitations of that implementation and then showing the better way.

[wbfaulk]

I remember dealing with all of these address locations when setting up hardware on pre-PCI, pre-Plug-And-Play PC clones, making sure you didn't have conflicts between your 16550A UARTs and your Adlib sound card and your whatever else. I had a solid _functional_ understanding at the time, but it's fascinating to learn what all of this stuff really meant. I would have loved for these videos to have been available to me back then.

[alanamcdonald]

I always appreciate the little mistakes that are left in, and showing the fixes. Your videos are wonderfully soothing and informative, like Mr. Rogers or Bob Ross teaching electronics.

[patrick_jane]

Only Ben can make a 20 min video fly by as if it was a 2 min video

[alexwolfeboy]

There is never enough Eater videos!! This series is awesome to see how everything’s built together.

[spritefun]

YES!! Thank you so much, Ben. I have learned so much about computers through your series, things i just could not wrap my head around before now make perfect sense. Looks like we have a new 65c peripheral chip to play with, I had a nightmare getting the 65c02 and 65c22 in WDC form, had to get rockwell versions instead from ebay.

[BillySugger]

Ben the little triangle within the device block more usually means the pin is an edge triggered input.

[abcrtzyn]

Absolutely perfect timing. I just got the MAX232 chip in yesterday, and was about figure out the the uart on my own today. Super excited.

[kevinjensen]

Hi Ben. I have been a hobbyist for almost 50 years and a professional electronic engineer for almost 35. I have enjoyed your videos because they go right back to bare bones. I use MCUs these days but I wonder if I would be able to understand embedded issues as well as I do, if I had not been a professional learning through the era of MPUs and discrete peripherals.

While I am loathe to make a criticism as small as this one is, I'd like to point out that it is not a good idea to tie two pins of a NAND or NOR gate together to realise an inverter. The reason is that the internal propagation time to each leg of the gate may vary in time, if only by pico-seconds. This can result in a glitch during transitions. Always best to tie one leg of a NAND gate high and use the other as the input to the inverter. That way there can be no race condition. Likewise, when doing the same with a NOR gate, tie one leg to ground and use the other leg as the input to your inverter.

I watched your peripheral driver videos for the USB, the I2C & the SPI bus. Having written drivers myself, I felt you explained these very well. If you have have time perhaps you could try the 1-wire bus. I have never had the need to write a driver for these but there are still plenty of peripherals for these such as RTCs, memory devices and sensors such as the ubiquitous DS18S20 temperature sensor.

Keep up the good work👍

[donprefontaine]

Finally! Got my hardware working at 0x7000, however the software does not work - not even loopback. My friend and I are looking forward to see how you handle it. Thanks, Ben.

[RobertMilesAI]

Excellent stuff. I kind of wish you'd left the mistake in place and tried to use the system though. I think there's a lot of value in that, for us to look at the weird behaviour and try to figure out what might be causing it, and to see how the process of debugging and troubleshooting this kind of thing works. I can imagine people getting one of your kits, hitting this kind of problem and then being totally stuck and discouraged because they haven't seen anyone successfully work through a situation like that

[stevedonkers]

I hooked up my 6551 to the 6522 chip to take advantage of the IRQ functionality. I've implemented my MAX3100 UART directly though. I understand using the WDC 6551 chip for teaching purposes but I highly recommend looking into other options.

[gregorymccoy]

I love these videos. My breadboard routing never looks as good as yours.

[danivation]

4:04 “supposed to have a bar over it but the bar kinda fell off” 😂

[anon_y_mousse]

I'd love to see how neatly you would solder all of these chips onto a perf board. Clearly your wire game is top notch.

[cheaterman]

Great episode! I like the parallels that can be made between your simple addressing circuit and the disjointed address blocks it creates, to the same type of addressing when eg programming for NES! (it is a 6502 as well after all, haha)
At 20:40 we can see your bus wiring is indeed getting untidy and hard to make sense of (even for you!), perhaps it's time you use the amazing trick with power-rails-as-bus you showed us for your computer-from-scratch series?

[КонстантинЧерныш-жз]

I was really looking forward to this! Thank you!