Come Back
Daves Lyrics

Jump to: Overall Meaning ↴ Line by Line Meaning ↴

You went away
I let you
We broke the ties that bind
I wanted to forget you
And leave the past behind
Still, the magic of the night I met you
Seems to stay forever in my mind

The sky was blue
And high above
The moon was new
And so was love
This eager heart of mine was singing
Lover where can you be

You came at last
Love had its day
That day is past
You've gone away
This aching heart of mine is singing
Lover come back to me
When I remember every little thing

You used to do
I'm so lonely
Every road I walk along
I walk along with you
No wonder I am lonely

The sky is blue
The night is cold
The moon is new
But love is old
And while I'm waiting here
This heart of mine is singing
Lover come back to me
When I remember every little thing

You used to do
I grow lonely
Every road I walk along
I walk along with you
No wonder I am lonely

The sky is blue
The night is cold
The moon is new
But love is old
And while I'm waiting here

This heart of mine is singing
Lover come back to me

Overall Meaning

Dave's song "Come Back" is a melancholic ballad about lost love and the memories the singer cannot let go of. The first stanza reveals that the singer let the person go but cannot forget the night they met, which still lingers in their mind. The second stanza describes the longing for the person and how heartbreak has left them lonely. As the singer walks, they cannot help but recall every little thing the person used to do and feel empty without their presence. The bridge of the song highlights the contrast between the vivid sky, the new moon, and the old love that cannot be forgotten. The chorus repeats the plea for the lover to come back, suggesting that the singer has not moved on and still hopes for a reconciliation.

The lyrics in "Come Back" use simple but powerful imagery to express the heartbreak and yearning of the singer. The mention of the blue sky, the high moon, and the eager heart in the second stanza creates a romantic atmosphere that contrasts with the sadness of the story. The repetition of "Every road I walk along, I walk along with you" reinforces the idea that the singer feels haunted by their memories, unable to escape the pain of the past. The use of the word "magic" in the first stanza suggests that the singer may have idealized their past relationship, making it even harder to move on.

Line by Line Meaning

You went away
You left me

I let you
I didn't try to stop you from leaving

We broke the ties that bind
We ended our relationship

I wanted to forget you
I tried to move on from you

And leave the past behind
I wanted to forget about our past together

Still, the magic of the night I met you
I still remember the night we met fondly

Seems to stay forever in my mind
I can't forget that night

The sky was blue
The day was bright and sunny

And high above
In the sky

The moon was new
It was a new moon

And so was love
Our love was new

This eager heart of mine was singing
I was filled with excitement and joy

Lover where can you be
I was wondering where you were

You came at last
You finally arrived

Love had its day
Our love was good for a while

That day is past
Our love is over

You've gone away
You left me again

This aching heart of mine is singing
I am in pain and feeling sad

Lover come back to me
I want you to come back to me

When I remember every little thing
When I think about everything we did together

I'm so lonely
I feel very alone

Every road I walk along
Everywhere I go

I walk along with you
I think about you while I walk

No wonder I am lonely
It's no surprise that I feel alone

The night is cold
It's chilly outside

But love is old
Our love is not new anymore

And while I'm waiting here
I'm still waiting for you

Lover come back to me
I want you to return to me

Lyrics © CONCORD MUSIC PUBLISHING LLC, Warner Chappell Music, Inc.
Written by: OSCAR HAMMERSTEIN, II, OSCAR II HAMMERSTEIN, SIGMUND ROMBERG

Lyrics Licensed & Provided by LyricFind

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Most interesting comments from YouTube:

Nezbrun

2y↑6

Absolutely right, I think it was around the mid 90s for me, I was brought up building and designing my own computers in the 70s and 80s. Once we hit 80386 protected mode and NT, and I could no longer bit bang the parallel port without having to hack a driver, I lost my grip of having a comprehensive understanding the entire stack.

I did write display drivers for Windows 3.0, but only a very few basic drivers for NT, and of course, the driver model kept changing. Thankfully since WinUSB we hardware guys can largely avoid writing drivers these days, but it's taken a couple of decades of USB to get here.

Regarding the PET's character display, AIUI the character generator ROM isn't memory mapped, it's on it's own private bus. There isn't enough time to be able to fetch the character and look the character's bit map up on the same bus.

The 6502 has a dual phase clock. On one phase, the CPU owns the bus (eg, instruction and data fetches/stores), and on the other phase the video can use the bus. As the clock is 1MHz, or a period of 1us, there's 500ns of bus access time for the CPU and then 500ns for the video. RAM and ROM of the day had typical access times of 250 to 450ns. By the time you've added the glue logic propagation delay times, there's not enough time to allow for any more than those two memory accesses inside that 1us.

Thus, to achieve the timing constraints of video refresh and the 1MHz clock, there's a second address/data bus, physically inaccessible from the CPU's buses, for the character generator ROM.

The dual phase clock of the 6502 architecture was a key reason for its popularity among manufacturers precisely because you could easily memory map the VDU memory and avoid timing contention with the time definite phases. Life was a bit harder for hardware designers on processors like the Z80 which doesn't have this feature.

The Embedded Hobbyist

My PET (CBM 4016, upgraded at great expense to 32K ) sits in pride of place on the top shelf watching this this video. Still connected to a Commodore 2031 single disk drive. it did suffer a dying video memory chip which i replaced, followed by the mains suppressor capacitor in the disk drive doing the normal thing of letting out the magic smoke along side some foul smell . :-(

Still have the great books by Nick Hampshire "The PET Revealed" and "Pet Graphics" and a very useful MOS Microcomputers "Hardware Manual" Rev A Jan 1976

A very interesting book which i used a lot when I used PET's in the test department was "PET Interfacing" by James M. Downey and Steven M. Rogers. 1981

These videos bring back a whole lot of great memories of using PET's at work and buying the one I still have.

please do more videos on the PET, I've done a few on getting mine back to working but we need more.

All comments from YouTube:

Nicholas Perrin

2y↑29

If the PET could use characters from RAM, it would have to access main memory for a byte around once every microsecond, starving the CPU like the ZX81 suffered. The C64 alternated accesses of main memory between the CPU and VIC, but that would have taken a lot of discrete logic chips to implement (which is why the VIC does so much in the '64), and probably faster ram chips, Ram chip access times from the 70's has alas faded from my memory..

Cowasaki Electronics

2y↑25

Literally the first computer I ever used and I’ve always had a soft spot for it. I rebuilt one recently on my channel (barely more than a 100 subs) but I got it like a museum piece. I have made the point many times that old 8 bit machines were totally different in that even as a teenager I could understand assembly language, understand the hardware and understand the OS. I wrote an expansion ROM for the CPC range that added 150 new commands whilst still at school and a disc copier better than literally any on the market for the BBC micro. Videos like this really take me back!

Hubster

2y↑13

A series on the C64 (assuming there is to much for a single episode) would be amazing. Interesting stuff as always look forward to seeing more in the future.

Steve Brecht

2y↑5

This is where I learned to code, ended up having 3 of them. A 2001, a uncommon Purple screen 4032, and a SuperPET 9000. I still have all three tucked away.

King ForADay

2y↑13

At one time the university I worked for moved from a mish mash of early computers, mainly the Commodore PET, to PC clones.
In the basement of one building they had several hundred Commodore PET's stacked with shrink wrap on wood pallets because they couldnt get rid of them!!!
No other institution wanted them. Illegal to send them to the landfill. They were offered free to employees and students but there were few takers, including me!
I believe they eventually had to pay a recycler to take them. These now sell for well over $1000 on Ebay!!!!! Coulda, woulda, shoulda!!!! AAArrrggg

Mark Lebowitz

I feel your pain. I still kick myself often for not taking the opportunity to snag my family's first computer, an Apple II Plus, when my dad was cleaning out his old house prior to selling it. I also enjoy watching videos of car enthusiasts restoring antique cars. Hearing restorers talk about their finds, I used to find myself shaking my head and wondering why such beautiful machines were just abandoned and left to rot - referring to both the computers and the cars. I have to stop myself and remember that at the time they were replaced, they were just old, obsolete machines, often crippled by problems that weren't worth fixing at the time. They couldn't run modern productivity software, Internet access was beyond them, and there were thousands more just like them here, there and everywhere, so unless except for special editions, they weren't worth anything. And a quick look at eBay suggests that these old gems, still aren't worth much to the market at large, and probably never will be.

I currently have a Compaq Deskpro from 1998 or '99 that was retired just a little over a year ago, long after most of its peers had been chucked. I'm currently using it to demonstrate some long-gone storage media to a group of high school students. I'm preservation-minded enough that I'm not going to throw that Deskpro out when I'm done with it, especially since it's in pretty good working order. As far as what I will do with it, that's a good question. It's too old to be useful, but too new to be a museum piece.

Jayson Larose

2y↑17

I miss when computers used to come with manuals. And those manuals had schematics.

Janek Winnicki

2y↑1

I was a 10 year old kid in Poland remember getting my first Amiga computer, accrualy my parents bought it for me.
It came whit thick books but didn't say much to an 10 years old kid from Poland. 😅
All I could understand was a page number.
Later i was looking at the pictures.

MrLunithy

2y↑2

I think the schematic for even a Z58 chip-set with a i7-2700k would be stupendous 🙄🤯🤔

Nezbrun

2y↑6

just42tube

2y↑3

It used to be more fun when we still could at least pretend to understand the whole stack from digital circuits to all levels of software. Becoming a software or system person was possible and even beneficial to start from digital circuits, hardware and moving upwards.

Jeffrey Phipps

2y↑2

This is so valuable. I also grew up in that era and slightly before. By the time I was teaching programming at university, students were already getting abstract information without any base history. It was a little painful to watch. I still teach, and I’m now having to make videos on steps to programming that I never thought would be necessary. Students come to my courses with nearly no understanding of what a computer is or does, even if they are reasonably good at using one. The horrors of tech support are hilarious reading, but also a tale of shame. If you get a chance to read Reddit’s tech support tales, highly recommended.

HALDikopter

2y↑16

Keep up the good work. Really enjoying your videos.

StarsManny

2y↑4

I'd love to see you walk through everything that happens from the moment of powerup, through someone typing PRINT "HELLO WORLD" on the keyboard, and finally hitting return and the output shows. It would be quite a journey!

Dave's Garage

2y↑8

Thanks for the idea! Not a bad one - could start with turning the machine on, then what happens until it goes input idle, then how it parses and executes the line of code. I'll think about that!

perry mahlmann

2y↑3

I used the kernel routines on the vic-20 to print to the screen, that way when a memory cartridge is installed and the screen memory changes the code still works as the kernel routine adjusts for that.

Geoff Seeley

2y↑2

The PET the was first computer I used and I was hooked when it dawned on me that I could make it do anything I wanted. I just needed to learn how and I'm still learning today thanks to the highly complex hardware and software systems of today. Today I'm learning about Serial Peripheral Interface (SPI) programming so I can unbrick a BIOS.

Paul Webster

2y↑24

Dave really should setup an old school BBS for his userbase (rather than a discord or other) I think it would go down pretty well :P

Perhaps not with a phone dialin though, some sort of emulation over TCP instead :)

Mike Whalley

I used to help a friend run an Acorn BBS with 3 lines, allowing a whopping 4 people to chat together - well until their parents got their monthly phone bill and banned them 😏

Dolphin Hates Hats

Even IRC would be a good midpoint, old enough that you can get old hardware to talk to it, but not that old that modern hardware can't also talk to it! You can even get smartphone apps for IRC, just!

Paul Webster

2y↑3

Infact ... it could be done, a standard BSD server, users sign in with ssh like expected, then they use minicom or such to a local BBS .... this must be tried!

BurnsyD 17

2y↑4

Love this retro deep dive, please keep them coming!

Darran Styler

2y↑2

I bought a second hand Pet in about 1988 off the company I worked for at the time. The only experience I had at the time was with cheap home computers such as the ZX81 and Oric 1, plus a week long 6502 assembly course when I was 13 in 1984. With no instructions, and of course no Internet it was a great learning experience. I actually managed to program a rudimentary BASIC horse racing game where you could bet on the outcome of each race, each horse was just the number 1-6 moving along a track made of the minus symbol and a random number generator to decide if each horse moved based on their odds. If I remember correctly the entire screen was redrawn at every passthrough of the code. Years later I managed to get a job in IT support but knowing how to code certainly helped my career, especially in the early days of DOS and UNIX support. Still dabble in C based languages to this day. Videos like this remind me of those days and how exciting computers were before they became a tool just for work, and help reignite the passion :)

Paul Stubbs

2y↑2

Nice, bring back the 8 bit days, I loved being able to have my head around 95% of my machine.
"Character gen rom not in memory map", same as my TRS-80 M1, having the actual character 'rom' in ram was a problem back then, the video refresh circuit has already pushed the CPU aside so at to read the video ram, now it has to also index back into ram to get the character patterns for that screen position, usually that was too much bandwidth for the main address bus to handle. I did it on as a hack mod on my TRS by having my programmable character 'ram' chip as a dedicated to character generation IC that was not 'normally' in the main memory map, so it's operation did not effect normal memory bus operations. However when I wanted the CPU to write to it, it was quickly switched from the video cct, back into the main memory map.
On my TRS, there was not a handy 2K hole in the memory map (I used a 6116 2k ram chip) so I mapped it ontop of the 12K Basic ROM. If you do a read, you get the ROM, if you do a write, if goes into the character gen ram. The only downside is that I could not read that ram, only write to it.
In the PET days, adding all of this would have made the circuit board somewhat bigger. By the time the C64 came out, Commodore were able to make their own custom chips, making this a lot easier, as the circuit board could be shrunk quite a bit. the downside for the C64 is a few 'unobtainium' IC's that makes repairs a tad hard. (yes I know there are modern solutions, now, - only due to the C64's popularity)

Trae Storm

2y↑3

Dave, from another old guy, you're the man! Thanks for thism it was great!

Dave's Garage

Glad you enjoyed it!

Brian Smithson

2y↑1

Dave is the man!! Really enjoy these trips down memory lane. I was a TRS-80 Mod-1 guy and loved Z-80 assembler.

aprofondir

2y↑1

Would love to see you collaborate with Bill Herd, he's an ex Commodore engineer (though he was there after the PET), he always has amazing stories to tell!

Rodney Smith

2y↑1

Thanks, Dave for yet another amazing episode. What a rich plethora of information that I, like most other grandpa's have forgotten or at least pushed further back into the recesses of near oblivion call my memories.

Peter Hodgkinson

2y↑6

Actually, I knew 99% of all that; but nevertheless the video was still fascinating and nostalgic.

Dave's Garage

2y↑5

I knew 90% of it and had fun doing it :-)

Locutus

I knew 100% of everything and still found it interesting. 😉

Boris Bosnjak

2y↑1

As a 14-year-old, I cut my coding teeth handwriting machine code and punching it into a ZX81 (and then a TS 1000 after I fried the ZX81 when clumsily trying to upgrade its SRAM to 4K :P). Your video reminded me of those old days when you could actually fully understand both the hardware and software of a machine. Zoom forward to 2022 and I have no idea how or what, let alone why, my Windows machine is doing what it is doing :S

William Topping

Awesome videos Dave. One thing I miss in life, is nerding out with other geeks and being so nerdy about it, it's unreal.
Used to take my Amiga to 'computer clubs' back in the day.

Dean Mires

Thanks, sir! I truly appreciate compressing my ol' brain cells dusting off the grey matter and making room for some new items in the cracks. I Didn't realize how similarly the Pet and TRS80 operated, though i did do some cross platform translations for a couple Avalon Hill programs. In those days, I treated other systems as "competitors" instead of embracing their similarities and treating them as cousins. {we do / should learn as we get older}. I wish that we could have shared corridors in Redmond. To stroke a well deserved ego, you continue to impress me, Kind Sir!

osgrov

2y↑1

I love this. I could listen to you for hours talking about PETs and C64s, and enjoy myself while doing so.
I hope you continue with this old school stuff now and then! :)
The PET was the first actual computer I ever saw and got to play a bit with, back in the late 70s. I was totally hooked.
A few years later and after endless begging, my father got me a C64. The world changed forever that day.

dan b

hear hear!

A Nother

In my early teens, I had a Sinclair ZX81, followed by two Atari 8 bits. Although I never got in to assembly language, I did have a lot of fun programming. Poking values from BASIC, altering characters, setting bits on the video and sound chips on the Atari to achieve different effects etc. References like "Mapping the Atari" and "De Res Atari" were incredible resources on the system architecture and OS, even if I only understood a fraction of it. Nowadays, everything is a black box, closed off and accessed by a gazillion gigantic libraries, and most kids today have no idea about bits and bytes.

BlauDrachen

Great video I love these kinds of deep dives and this one was one of your best videos yet. Thank you Dave.

Ian Rolfe

2y↑1

The reason the PET didn't have user defined characters is that the character ROM isn't in the 6502's address space, it is hard-wired into the video circuitry. You can't read the character ROM on a PET from a program even if you wanted to. The video circuitry in the PET essentially operates asynchronously on its own, with the CPU grabbing access to the video RAM when it wants it - do this at the wrong moment and you'd see "snow" on the screen where the wrong data gets shifted out to the electron beam! That is why BASIC usually waited for the vertical retrace interval before writing to the video memory.
Later PETs, the 16K and 32K pets (2016, 2032, 3016, 3032 etc) did use dynamic ram. These are often referred to as the "Dynamic PETs" by forums.

Troy Frei

Another great video. I can remember programming on a TSR 80 using the basic I/O using the Peek. And Poke. One of those wrote to the screen memory the other one read the joysticks or keyboard.

Dean Mires

My first production computer was the TRS80, Model 1, And with the exception of the Z80 processor vs 6502, I never realized just how close the TRS80 was to the C64 in operation. Similar (but different) Memory map different , and other functions. I'm grateful that I learned programming in those days - i still shake my head looking at programs that are written in multi-megabytes and even a few in the Gig ram size. I wrote whole applications in 32K, let alone 48k and multi floppy drives ... everything from payroll to inventory. As well as interfacing the TRS80 to alarm systems that tied into the payroll system, or 'call for the cops' if the wrong person came in after being fired, and use the data for payroll. I miss the days of interfacing a model 11 to a Helicopter simulator. not just a 'flight simulator' rather a trainer for learning and testing on 'Real Hardware'.

codingbloke

Loved the PET. Cut my programming teeth on it at School. Ducking out many other classes to be found in the computer lab (2 PETs) coding away with no idea what I was doing but generally succeeding anyway.

karehaqt

As someone with no technical background I still enjoy these videos because Dave is a great storyteller.

SeanFromPVD

When you mentioned the part about not understanding some of the other sublayers and bits of the system, it got me remembering a thing I watched a while back about ALSA (Advanced Linux Sound Architecture). The discussion was about how without some kind of added layer of control modules and extensive system components in the middle of him and ALSA - he would have virtually no idea how to make it useful. And that's just the sound. Imagine also trying to interface on a machine-code level with a modern graphics card, with all of their complex functions. 😳

Everything has been reduced to specialized modules that entirely do things for us. The problem is that those modules are extremely power-hungry, when you consider resource uses.

I started using computers when an entire OS would boot from a floppy. Now single video games are significantly bigger than most of the hard drives I used for the first 10 years of using computers. 😳

John Boyett

Fascinating video! I'd like to see more like this, specifically on Radio Shack TRS-80 computers if possible, since that's what I grew up on. But these Commodore videos are equally fascinating to me as well. Keep up the good work!

Carl Seiler

2y↑1

We had a PET 2001 and PET 4032, and I knew about as much as could given the documentation I had, but it was clear that there was lots that was missing and either in documents I clearly could not put our hands on or in documents that did not exist for the general public.

Simon McD

The book "Microprocessor interfacing techniques" by Rodnay Zaks is a great introduction to this kind of stuff, first published in the late 70s, it's a brilliant read

CallousCoder

I concur! I love the C64 because I pretty much knew every detail and if I didn't one book would explain it. And I was amazed that I knew most od the addresses are 35 years later, when I picked it up again 2 years ago. The Amiga was already far less the case for me.
And it actually taught me how to make my own little computers/controllers even before I studied EE. And often still helps me investigate problems.

Keith Gaughan

An interesting machine to compare with the PET regarding its internals is the Jupiter Ace. In some ways, it was simpler - it was explicitly a home machine - but it made some interesting design choices to control cost while attempting to keep it competitive with its competition at the time, such as the ZX81, including its use of Forth.

Mind you, the machines themselves cost a fortune these days, so an emulator or FPGA core for the MISTer or the like is a better option.

JoOngleGamer

Commodore's way of editing was so underappreciated, but so innovative.

piwex69

2y↑1

"Standing on the shoulders of giants" - great write up!

Jeffrey Phipps

Something I constantly have to teach students - input/output. They get that a little with PHP or with CICS. But in normal programming, they ignore the WFA form (or WPF, etc.) until the last minute. I was always taught to use spacing charts to plan I/O before coding (partially because it helped plan some of the variables).

MobSlicer152

2y↑1

Cool. Would love to see one on early x86 machines too.

Thomas Albech

2y↑1

Very well presented. I admire your dedication to these legacy systems. They serve well as a way of explaining the basics of computing. I really enjoy your channel.

Dave's Garage

Thanks for the kind words!

MrLunithy

I think it would be down to run time and the timing limitations like the much later Amiga it only worked as well as it did with custom chips for sound and video not having to register major actions through the CPU.

Fred Flintstone

Thanks for the walk down memory lane. I started with the Commodore 64.
I recently did a hobby project for my IBM PC-XT and wrote an assembly language program to interact with the battery backed up clock board on the IO buss. The original program was long gone from the hard drive which required low level formatting to bring back to life.
I had to trace out the board, create a schematic, and then look up the spec sheet for the chip (MM58167). I used MASM to write the code. The project was very satisfying an a lot of fun. The last time I did any assembly language coding was 30 years ago.

Lucid Moses

I know someone that had a CMD 8032. He had a bunch of chips he would swap out to change the font. He also had a toggle switch he added and in one stat you got the regular rom font but in the other the font was software controllable. I've done a fair bit of bare metal programming but I'm not a hardware guy so I don't know how he accomplished it. Now a days you likely could find instructions on line.

Andrew Beasley

Great to see the Pet getting some love rather than games machine.
Please continue in this way - maybe discussing how you could off-load code to be run on the disk drives and how I/O could connect to lab equipment.
Maybe build a 6502 SBC at the end running Forth of course via a terminal (much more fun than Basic)...

EinChris75

Ben Eater has an awesome series of videos how to make a tiny computer based on the 6502 and bread boards. If you like Dave's videos about that topic, Ben's are a must to watch. They are maintained as a playlist on his channel.

Bryan Stark

Very interesting topic and I was hoping to use it to understand why some code works on 32-bit but not 64-bit. For example when passing a Long vartype in VBA in a 64-bit, the equivalent is LongPtr, however, according to Microsoft this is still not equivalent but it's used to transform a 32-bit Long into a 64bit LongLong, which still isn't the same and that is very confusing. It's why porting code that was written for 32-bit machines into 64-bit machines, isn't always cut-and-dry. I'd like to know if you have experience with this and why it seems difficult to port code into 64-bit machines.

nkronert

The C64 reference guide is almost certainly the one book in the world that I spent most time on reading. It was like a treasure map for me.
Great memories.

Gergely Feldhoffer

7:34 I think it is a bit misleading to show the electron gun to cover a full character as the scanline went through all characters first row altogether. I am curious if there was any caching like mechanism here as the video control had to access the same N character bitpattern 8 times.

Ian Taylor

Excellent description Dave, thank you

Derek Carr

Dave, I just have to mention how great that jacket looks on you. Also love the video!

Dave Pin

The Compukit UK101 had peek & poke in BASIC and so having a memory mapped screen it was possible to read and write to the pixels.
1k RAM standard expandable to a max of 4K.
I had 4K and wrote many programs.
Few needed more than 1K.

JennyKayla

Oh memory lane. Copying the char table to ram and editing it. I spent a lot of time on a C64. Students today don't know the relationship between the various components. Thanks for this video Dave.

Menschgebliebener Szene Casher67

This guy must really love his pet :^)

Dean Horak

2y↑4

Re: character generator ROM:

My guess is that allowing both the CPU and video circuitry y access the RAM would require additional circuitry to implement a dual-ported RAM solution - adding cost to the system.

It was also the case with the TRS-80.

Per Westermark

@Greg Mark Yes, it was SRAM. I wouldn't want to try DRAM, because of the additional complexities - it was over 35 years ago and before I learned how to use programmable logic. So lots of 8 kB SRAM and UV-PROM chips and a a big wire wrap prototype board. Z80 CPU, CTC, PIO, SIO and 6845 CRTC.

The next project was to write a Z80 simulator and make it into a ZX Spectrum simulator. I got as far as having it print the copyright message upside down. Unclear if it was a bug or an ertor in the Speccy documentation I used.

But it's always fun to try projects that are a bit outside of the current skill level. It's an efficient way to learn.

Greg Mark

@Per Westermark I assume you're using SRAM? Cause I'm pretty sure it gets a lot harder when you have to work in the dynamic refresh cycle, as well as both CPU and vid access...

Per Westermark

@d2factotum That is why MUX chips are needed, to switch ownership of data and address lines. And a means ti synchronize the code with the horisontal and vertical retraces

Per Westermark

@Wholly Mindless Yes, contention is definitely the issue. But there is a cheat possible in some situations.

During CRT horisontal and vertical retrace, the graphis do not need to read out data. So it's possible to switch ownership for accesses.

Not a perfect solution for graphics RAM since it limits available draw time per frame. But enough time to redefine sprites in a RAM-mapped character generator.

Edit: but it does require some MUX chips to switch if addresses comes from CPU or CRTC or whatever is used to drive the graphics display. And it requires an extra dual-direction buffer chip on the data lines since the character generator data must be muted from the CPU data bus while graphics is being emitted. Easy to build but adds cost and PCB space.

d2factotum

I may be wrong, but I think the character ROM on the PET (unlike the C64) was not hooked up to the main CPU--it was only attached to the CRTC. So, the actual hardware made it impossible to relocate the ROM.

2 More Replies...

John McKown

I had the Tandy Radio Shack TRS-80 and got the expansion box. I had 48K of memory! I got a board from a company named "Parasitic Engineering" which remapped some memory and put in a replacement BIOS so that I could run CP/M-80. I eventually got a PC clone due to my boss' insistance. I wanted an Amiga.

monomonster

I knew my CoCo 1 and 3 inside and out. I could write BASIC and ASM while in my sleep. I even took a broke CoCo 3 and made the case into a detachable keyboard for my 512k CoCo 3. And my Tandy 1000TX, I knew how to upgrade it and adjust every jumper on the motherboard.

Willem Kossen

Would be interesting if you did something similar about the arduino system.

MadEzra64

That jacket is the definition of old school cool. Nice touch, Dave!

tripplefives

I'd say that the cost of ram prohibited ram based font generator. It's likely that because its an early model it was designed as a series of steps and its easier to test each step when there are few dependencies (the font ram would depend on the cpu and ram steps which creates a circular dependency and makes design and testing more complicated).

John Spence

Nice! When computers were more art and generally out of the reach of most people. I started with a Apple IIGS

Stefan Berndt

There are several reasons for not making RAM useable as character generator.
On the C64 the CPU and graphic chip share the same Address and Data bus. So the CPU can read char rom and the graphic can read the main RAM. Since you have to avoid same time access to the bus of both CPU and graphics, there have to be some synchronizing mechanism. On C64 the graphic chip can simply get exclusive access to the bus. If the CPU needs some data, it have to wait. This is why most fast disk loader turn off the screen. To make the CPU run at a more constant speed.
As you describe the PET, there is a divided CPU and grapics bus system. The CPU cannot read the car rom, and the graphics cannot read the system ram. Seems the screen ram is a special dual channel ram who acts as interface between cpu bus and graphics bus.

Daniel F. Smith

Re video RAM: I would hazard a guess that the hardware engineers couldn't get the video generator to multiplex with the CPU address bus nicely. Easier to place video ROM on its own bus than mix bus masters. (I seem to recall that some 6502 systems alternated the address bus owner every cycle.)

Anonymous Delegate

“I absolutely guarantee that you will understand a computer at a new level”

not a guarantee

🤣

ThatCreole

Please do! Love the content Dave!

dan b

My first computer was the TRS-80 Model II - I'm fairly certain I had the most important main bits saved in my memory! *(at the time... Now not so much...)

The Embedded Hobbyist

Steve Johnson

Life was good when I could stop toggling the boot loader into the front panel of a PDP-8, and use the boot loader in Core RAM in a PDP-11. Imagine my delight when the bootloader and monitor were burned into EEPROM in my 1975 Digital Group Z-80 computer that I hand-soldered together, all 1024 bytes of static RAM, later expanded to a voluminous 8 kbytes. It would load and save using audio tape. I wrote a lobby kiosk annunciator board app, in hand-written machine code, for that sucker.
Booting Windows or Linux from SSD is an incredible luxury! (By the way, get off my lawn).

Marc Wolfe

I know enough to know that the things I don't know could have been designed dozens of different ways. Going over possibilities for why I couldn't get a Tesla M40 going. Ended up getting it going with latest BIOS update that came out a couple weeks ago.

Howard Hammermann

Yep..Me too.... The Commodore PET was first ever computer that I used as well. I was working for Lucasfilm and George Lucas bought one in 1978, and gave it to me to use... It was fun! I decided that I would try to write a program to inventory all of the spare parts in the Post Production Engineering Department (Me! 🤣) and soon realized that there was simply not enough memory (we had the 8K RAM version) to hold all the data. The cassette drive was not so helpful, and it was also pretty slow... Oh well... Many years later the company graduated to a VAX 11-780 and that was much more useful to me! (And the Computer Graphics Division...) 🤣

Joel Edem

lmaooo that winning by default joke about jeopardy made me laugh a little too hard . did not expect that punchline . Great videos as always

Dan Shirley

This is interesting. Am I wrong in thinking though that the whole screen would be written line by line - it's not like a scope - so if you had a line of text (ABCDEFG) it would write the top line of all of those characters in a a row, then the next line of all those characters etc. So it didn't actually steer the beam - it did it line by line like a normal crt?

Opop Opop

This was the first computer i used. So I probably know just about everything you are going to share :) YET when you get to our age MEMORY can sometimes be an issue, go givin er a watch, and thumbing you up while I do so!

Friendly Neighborhood Jesus Freak

I think GW-BASIC had a slightly more advanced version of the screen editor.

I know the Apple //e, but since it has Microsoft Basic and a 65C02, it's not really that different under the hood from a PET. ;)

neilbradley

2y↑1

"I think young developers in particular are worse off because of it." <--- This right here.

brocktechnology

I believe "c" is the current version of the rs232 standard witch has never officially allowed 5v signaling although it's very common now. I am not a reliable source for this.

SassyToll

Thanks Dave!!! Great job 👏 👍

Yukito Atari

Has a keyboard reverse engineer, who work to convert old keyboard and typewriter to usb, it's not easy going back to basic.

Dan Goswick

Nice video Dave!

Paul Edwards

Indeed, things rapidly became complicated. Perhaps they just did not think of it from lack for experience, a movable pointer to a character matrix. Atari did it because they were in the video game… game.
Perhaps a video about your development work on your Amiga products. Not so much to be focused on the operating system or hard ware but the fact it was multi tasking without any memory protection or resource tracking. Topical as it was the ultimate case of a system being open to pointer goofs, the cause of almost every security exploit we suffer from in the software world today.

Kevin TeStrake

I remember cutting my teeth on a TI 99-4/a back in the day. I didn’t understand it at this level, because I was too young and there wasn’t an Internet. BBSes came a bit later for me, but the early days were spent in TI Extended Basic.

Thanks Dave, for shedding light on the old school.

Ma ON

Back in the day, memory was VERY expensive. Decisions were made with the intent of conserving memory.

stonebleeds

Please do more like this

Stoney_Eagle

2y↑1

And after all these years 0.1 + 0.2 is still not 0.3 😂

electronron1

2y↑1

I miss the old days when a hacker was someone who would piggy back chips, cut traces and run some jumpers to add features or access features the manufactures decided not to make use of.
The TRS-80 had lower case in the ROM but descending characters(g,j,y) couldn't descend so that part of the ROM wasn't used. Using some unused logic gates on the boar and a short piece of code written in assembly language and you now had upper and lower case characters, at least until you turned off the power.

Dave's Garage

2y↑2

I was just doing that... piggy backed the 74LS145 keyboard chip I'm fighting with, then bent one leg out of the socket to test that line. It's not smart or right, but it's fun :-)

Channel Zero

I can make a BASIC Commodore 64 program but I never learned any POKE commands except the one to change the screen colour. I’m Australian and we have the extra U too! Anyway, as long as you don’t want fancy graphics or sound, I’m pretty sure I could knock up any program you need. Mind you, I think trying to make a spreadsheet application in BASIC. I’m not sure I ould do that. It would be interesting to try. Anyway, I’m just leaving a comment to boost user engagement. I love this channel and I loved this video. Yes, more, please!

blue solder

I remember the C64 as having static RAM not dynamic, specifically 2114L-30 RAM chips

Dave's Garage

2y↑1

I think just the color ram, but I could be wrong. I was fairly sure the VIC chip did the DRAM refresh.

Keith Gaughan

One of the key design differences between the VIC-20 and the C64 is that the C64 ended up needing DRAM to keep the cost down. The VIC-II handles DRAM refreshes, which is probably why the C64 can't have the concept of "contended RAM", as all RAM is contended on the C64. Imagine what could be done if, as with the Spectrum, only the bank of memory shared to the screen hardware resulted in a slowdown: while you wouldn't be able to double the 6510's clock speed - some bus arbitration still needs to happen, it would've allowed a nice speed bump to the machine.

piwex69

2y↑1

just for the screen color memory afaik

Robert K

Interesting differences between what you say on-screen and what the subs say :-). Also, the subs spell kernel as KERNAL (including caps) all the time. Just a nitpick but I suspect it would annoy you as well, Dave ;-). Nonetheless, another fine piece of infotainment! Thanks Dave.

Dave's Garage

2y↑2

The correct spelling is KERNAL :-)

Mike's Vegan Life

If you really want to get deep, you should also understand how electronics were, how voltage works, how transistors work, resistors, and various devices. Because all those fancy chips are just made up of some of those devices, and because of that many of their limitations are bound to the limitations of saying how transistors work. For example, why refresh memory? Well because if you don't it'll forget. Ah yes, but why does it forget? And further, how does it remember at all? We need a CPU processor designer who is as interesting to listen to as you are.

EJ Harrop

Thank you, my brain hurts in a nice way. Cheers

Matthew Suffidy

Actually the no one person argument is becoming interesting in the ability to actually do crazier things like genetic engineering. Is this really doable?? seems to be working in computers.

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