Oh the memories. In the late 1970s I had some schematics to build an 8080 computer. I thought I would go leading edge high tech, changed things up and built a computer based on the Z80. I used wire wrap sockets. I eventually got it working. The 2k static ram and an eprom was all I could afford for memory. I skimped on the toggle switch interface and just used 3 dip switch modules. I got pretty fast at programming by flipping dip switches with the end of a pencil. My intent was to put together a bank of 16 + 8 toggle switches and plug into the dip switch sockets but I never got around to it. I got it out about 20 years ago and it was still working. This video is motivating me to dig it out again and carry on with my decades old project.
I had a buddy that created a flash strobe controller board using an EPPROM. His project was crashing each time the strobe ignited. He searched and searched, convinced it was a power surge making his board crash. Finally found it was the light hitting the EEPROM just enough to crash the memory but not enough to erase it. Make sure those stickers on the EPROMs are really opaque ! 😂
Back in the late 70s I built a Z80 computer using 24 by 1*16k 4116 dram chips (48k). The site where I worked had a fab plant and rejected 1000s every week, I grabbed a few most worked well enough (they were so expensive, no way could I afford them). It also used 2708 UV eproms 1k * 8 (27V programmable). About 5 years ago I pulled it from the garage, I replaced 2 faulty dram chips, a UART and some power supply caps. The main issue was not having an analog TV to hook the RF video into. I used an Arduino nano to convert the parallel data into the video controller into serial USB for connecting to a pc. Every few months I fire it up, it's still working after 40+ years.
For someone starting playing with these as a hobby those 28 series EEPROMs seem to be the ticket. Also even though I've been looking at SRAM and EEPROM chip datasheets this whole covid summer, this hands-on run-through really made this information in my head a lot clearer. Great vid thanks!
Because my first programming for my Father was an HP plotting calculator, I invented my own Reverse Polish Notation Interpreter as an extended emulator for HP. Never did Forth itself, but yeah, awesome.
I have great memories as kid in the late 70's of buying and soldering 2114 static RAM chips onto a memory board to get my computer up to 16K of RAM. Each chip was half a kilobyte and sucked a ton of power. Just ten years later I could buy eight chips to get 64K of RAM which would have been 128 of those 2114 chips.
Good for you. I have the thought that everyone who wants to use a PC should have to assemble one of those systems in order to get their 'permit' to operate a PC (not exactly the language that I'm looking for, so jj) (or at least have to set up a modem and make it work to connect to the internet.). I put my first "PC" together in 1977 with a soldering pencil (Altair) and looking back on it, it was a lesson in insanity (I was 13 at that time) and those things were just crazy to even get started up . It took me a year to get everything together but I certainly did. The hardware that you have is incredbly beautiful compared to what I was working with at the time. I'd have never thought that we would make so much progress so rapidly...
Bank Switching. That's where some memory chips occupy the same address space as others, but there is a way (often through using I/O ports) to switch the access signals on or off so that only one set of memory chips get the access signals at any time. With the Z80, it was common on multi-user systems to have 16K of common memory occupying the top of the memory space and the bottom 48K of address space could be switched in 16K "blocks" to provide 128K or more of virtual bank-switched memory. Whenever the OS time-shared to a different user's programs, it would switch out the previous user's programs and switch in the next user's programs by bank switching the RAM.
I use Arduino Mega as system controller, to preload ROM image into SRAM (with Z80 in BUSRQ state), before letting Z80 to start. So, need no ROM, yet. Z80-MCB2 uses similar method start-up method.
Wow, man does that take me back! I cut my teeth on the Commodore C=128. I had just become disabled, and about a year before had purchased a 128 for my kids. Well the 128 became my entertainment system as the doctors worked on getting me back on my feet following a line of duty accident while working on the police force. The Commodore came with an extensive book on how to program with BASIC, and with nothing on the TV but soap operas during the day, I found myself teaching myself basic. Soon it became known that I knew about computers and folks with every sort of PC were calling me to come to their businesses and work on their early computer systems. Most were old IBM machines as well as the occasional Compaq running CPM so I learned those Operating systems as well. Now I play with micro controllers as I am not that far behind you in our hobby. Thanks for the great videos! They expand my learning from long, long ago.
Randomly came across your channel in my recommended feed and have really enjoyed the couple of videos I've watched so far. Subscribed and looking forward to seeing more. Cheers!
Very good. Back in the early 80s I was doing something similar with the 6502. At that time the smaller capacity 6116 ( 2k x 8 bit ) sram was more affordable. But my application was embedded inside medical instrumentation, so one 6116 and a 2764 EPROM was enough
12V for programming? I remember when it was 25V. I built a programmer that worked with an Acorn Atom in the school computer class, the thing was entirely software driven, having the 8 bit data from the user port and 3 lines from the printer port (reset counter, step counter, program pulse). The programming mode was armed by a switch on the unit which engaged the VPP supply - a really weird setup that used a 6-0-6V transformer driving a bridge rectifier from half of it and a voltage doubler from the whole, adapted from a circuit I found for producing a parasitic negative rail with a FULL BRIDGE RECTIFIER providing positive Did it get used for nefarious purposes? Of course!
As even 512KB SRAMs are dirt cheap these days (AS6C4008 5V 32 pin PDIPs are sub $7 in lots of 1) then you might as well add a little extra hardware and use bank switching.
The 27C256 without the window is still an an EPROM, same as the 27C256 with the window (except no way to erase it). The windowless version is referred to as OTP - one time programmable. They were cheaper than the erasable versions. The ones I had at work were plastic packages rather than the ceramic packages of the windowed chips.
Weird that this has popped into my feed lately, but I like it. :) Also, another possibility for a ton of storage is the M-Systems DiskOnChip 2000. It comes in the 32pin (sorta) standard JEDEC pinout and is mapped into 8k of address space. They're usually used in PC/XT's for solid state storage, but I have seen them used in embedded MIPS/Power architecture machines. They are 8bit, so there's no reason they can't be used in Z80, 68k, etc.
My Z80 computer uses a 128KB Flash ROM, the SST39SF010, like all of my 8-bit computers. I guess I'm just different. However, I can use jumpers to select between 8 different programs from the same chip, which is pretty cool.
On my Z80 Playground system the options I went for are 64K ram with 32k rom overlaying part of the ram. You can then switch the rom on/off from software. I think this gives the best range of options, as you can copy part of the rom into ram then turn the rom off. You can see it here: ua-cam.com/video/y9HNbJzdbpE/v-deo.html
On my selfmade Z80 I used M28F101 FlashROM and MCM6206DP20 SRAM, both from scrap computers. That was back in year 2000. Too bad, on todays scrap computers you will never get components like this.
@@KennethFinnegan I originally purchased an AT27C256R but then realised it was 1 time programmable. I also think it might need a 12V supply for programming. So I've now got an AT28C256 which I believe can be re-programmed multiple times and only requires a single 5V supply. I'm still uncertain about this stuff and have not used either chip yet. But it is the next job on my list.
If you don't have old chips to start from, the 32-pin flash chips are a good way to go. Cheap and lots of capacity. Nearly the same pinout as the 28 series EEPROMs
I've been looking for my "perfect" hobby computer. I can't really decide if I want Z80 or 6502 based CPU. I built Ben Eater's kit, but got tired of futzing with the breadboard connections. Removing the ROM over and over again to program would pull some address lines. I just want a simple computer that I can hold in my head while programming. Eventually, I'll learn enough KiCAD to design my own with a ZIF socket for ROM and maybe a built-in max232 so I can just plug in a usb cable for power and comms. Maybe the RC2014 would do for my wants/needs but, I'm not really interested in running retro software so the memory map doesn't need to match old systems. Z80 is interesting because there are models that run 20MHz and I/O isn't necessarily mapped into memory space.
I have a couple of EPROMs and I wanted to erase them, but I don't own an eraser for them. I don't really plan on getting any more since the flash chips and eeprom chips with the same pinout are usually cheaper, so I left them on the deck in the sun for two days. No bit flips, all the data is still there...
If the Zilog Z800 had been used as the default chip for all home personal computers then maybe they might have been on a power with the likes of Motorola 68000 with the ability to do multiply and divide without having to reinvent the wheel.
i'm using an Arduino Nano instead of an EEPROM for my Z80 project. Problem I had had is, the Arduino is not a tri-state device. The digital pins behave OK input mode, but the analog pins still draw too much current in input mode and therefore kept pulling my data bus down. I found a 74LS245 bus transceiver didnt work satisfactory, but 74ls241 buffer does enable me to bridge the Arduino Nano to the data bus. Bonus for using the Arduino Nano is, My "ROM" emulator code can also disassemble on the fly, which has been amazing for debugging (helped by M1 signal) This is limited to 512 bytes of address space for Z80 code on the Arduino, but my Z80 assembly coding is pretty awful and I havent written a program that big yet lol
I had fun with a Z8 chip which has onboard Basic. For memory I use a 32 kB SRAM that was wired to appear as ROM in the lower 32 K and as RAM in the upper 32 K. Unfortunately the breadboard wiring put too much of a capacitive load onto the Z8 and it overheated and failed. Were I to experiment again I would devise a PCB, not use a breadboard.
one problem with uv eproms, especially lower capacity and 'older' type numbers is they need fairly high voltage to program, and many modern programmers cant do them ... and not all of a particular type number are the same , some manufacturers may use different programming voltages to others...
I use EEPROMs as they're simpler to reprogram. So I am curious why you use EPROMs, is their an advantage over EEPROMs? Edit: Never mind, you addressed it at the end of the video.
You know, if you put a battery on the power pins of one of those 64k byte chips it becomes a permanent memory device (as long as the battery holds out). Write whatever "ROM" code you want to it and use the rest of it for RAM. Suddenly you have a full compliment of memory (both "ROM" and RAM) in one chip. Yeah it will take a bit of finagling with the power pin. But so what. A simple diode to keep it from feeding the rest of the circuit usually works. Play with it.
Is there a single chip solution that read and writs like ram but also holds its memory? bettery backed stuff makes me iffy. a z80 board with a single mem chip
Not sure if it exists but a chip with 8K ROM (erasable) and 56K RAM in 1 chip would be nice to cut down on components and wiring. Maybe only suitable for hobbyists so not economically viable. Or other combinations like 16/48 etc.
Hmm, I thought you might have covered pagable memory. Way back in the day I had I think it was a TRS-80 Model IV that had 128K of memory and I seem to remember that it could legally or by hack was expandable to 265K. This was before the IBM PC's really were released. Mine was 64k on board but if paging was enabled and the address pointer was pointing to C000-FFFF it would use whatever was in the D-Latch. So even though it was 16-bit addressing for the CPU it could be tricked to use 20-bit addressing by a hardware trick. But you only could access it in 16k pages. Most of the time it was some sort of data as you couldn't point a program counter to it and think it would work but I guess if you were careful in it's design that would be possible as well. The problem that would have to be solved is that's where CPM placed it's kernel was in the upper memory space so you would have to move it in memory so it wouldn't cause a problem.
Never heard of it. It seems to be a variant of 29F series flash? And yeah, 29 series is a perfectly valid choice that I just didnt happen to cover in this video. Particularly handy when you want to be able to save back to the chip on a running system. I'm tinkering with a 29C010 chip to see if I can get it working as persistent storage for this computer.
@@KennethFinnegan well, 39SF is still manufactured, and can be purchased on DigiKey for under $2. As of "storage", you could play the NES trick and just use 6264 RAM with a simple 3.3V lithium battery to hold it up. That's how Legend of Zelda, for example, worked.
I use 39 series ROMs in my projects. They are quite cheap for a lot of bits, even if you don't need to use them all - just tie the unused address lines low, or to some headers or other logic for banking/paging. I've also got a collection of 27 series with windows that I have pulled from electronics over the years, but no eraser (yet). I may get one in the future if I want a really retro look for one of my projects, but for now I consider them a bit of a faff.
so: prom = program once and it now is rom eprom = use uv light to erase then can be reprogrammed eeprom = you can use electricity to erase and then you can reprogram i get that right? 0:-)
Is there a fully static core version of the Z80? I wanted very much to do some Z80 projects but I had to switch to 6502 which seems to perform well at very low clock speeds, while the Z80 became unstable.
Yes. That’s the joke. You know some poor bastard needs rom 3 of 6 to get his gear running. And you erased it! Lol!! I like your vids. You were a YT random for me, now I’m here. Thank the Google.
Haha. Fair. Pretty much all of them came from work, and I don't think they would have appreciated me posting ROMs online for prototype builds from the 90s. Glad you're enjoying it here! :)
i havent blown any chips due to static ....yet...... worst thing is when you buy them and they arrive stuffed in a bit of polysytrene, instead of something reasonably antistatic ...
Yeah. Depends on your needs for the project, but the main thing is to appreciate that all of these SRAMs are about the same price, so no point in using multiple lower density chips to save money like many of the original designs recommend. If you want 64k of RAM, get a 64kB chip. I just didn't happen to have any 64kB wide DIP SRAMs, which is why I showed an 8kB SRAM. I haven't happened to buy any of this; all from e-waste.
Oh the memories. In the late 1970s I had some schematics to build an 8080 computer. I thought I would go leading edge high tech, changed things up and built a computer based on the Z80. I used wire wrap sockets. I eventually got it working. The 2k static ram and an eprom was all I could afford for memory. I skimped on the toggle switch interface and just used 3 dip switch modules. I got pretty fast at programming by flipping dip switches with the end of a pencil. My intent was to put together a bank of 16 + 8 toggle switches and plug into the dip switch sockets but I never got around to it. I got it out about 20 years ago and it was still working. This video is motivating me to dig it out again and carry on with my decades old project.
A couple hours of bright sunlight will erase the 27 series prom.
I had a buddy that created a flash strobe controller board using an EPPROM. His project was crashing each time the strobe ignited. He searched and searched, convinced it was a power surge making his board crash. Finally found it was the light hitting the EEPROM just enough to crash the memory but not enough to erase it. Make sure those stickers on the EPROMs are really opaque ! 😂
Back in the late 70s I built a Z80 computer using 24 by 1*16k 4116 dram chips (48k). The site where I worked had a fab plant and rejected 1000s every week, I grabbed a few most worked well enough (they were so expensive, no way could I afford them). It also used 2708 UV eproms 1k * 8 (27V programmable). About 5 years ago I pulled it from the garage, I replaced 2 faulty dram chips, a UART and some power supply caps. The main issue was not having an analog TV to hook the RF video into. I used an Arduino nano to convert the parallel data into the video controller into serial USB for connecting to a pc. Every few months I fire it up, it's still working after 40+ years.
For someone starting playing with these as a hobby those 28 series EEPROMs seem to be the ticket. Also even though I've been looking at SRAM and EEPROM chip datasheets this whole covid summer, this hands-on run-through really made this information in my head a lot clearer. Great vid thanks!
That's what Ben Eater is using for his 6502 board
Ha Ha, just got to the bit in the video where Ken mentions Ben Eater and his using EEPROMs :D
I highly recommend investigating Forth as a fascinating alternative to / marked improvement on Basic.
Because my first programming for my Father was an HP plotting calculator, I invented my own Reverse Polish Notation Interpreter as an extended emulator for HP. Never did Forth itself, but yeah, awesome.
I have great memories as kid in the late 70's of buying and soldering 2114 static RAM chips onto a memory board to get my computer up to 16K of RAM. Each chip was half a kilobyte and sucked a ton of power. Just ten years later I could buy eight chips to get 64K of RAM which would have been 128 of those 2114 chips.
These SRAMs can be found on 386 and 486 mainboards. They are used as external CPU cache.
Good for you. I have the thought that everyone who wants to use a PC should have to assemble one of those systems in order to get their 'permit' to operate a PC (not exactly the language that I'm looking for, so jj) (or at least have to set up a modem and make it work to connect to the internet.). I put my first "PC" together in 1977 with a soldering pencil (Altair) and looking back on it, it was a lesson in insanity (I was 13 at that time) and those things were just crazy to even get started up . It took me a year to get everything together but I certainly did. The hardware that you have is incredbly beautiful compared to what I was working with at the time. I'd have never thought that we would make so much progress so rapidly...
Bank Switching.
That's where some memory chips occupy the same address space as others, but there is a way (often through using I/O ports) to switch the access signals on or off so that only one set of memory chips get the access signals at any time.
With the Z80, it was common on multi-user systems to have 16K of common memory occupying the top of the memory space and the bottom 48K of address space could be switched in 16K "blocks" to provide 128K or more of virtual bank-switched memory. Whenever the OS time-shared to a different user's programs, it would switch out the previous user's programs and switch in the next user's programs by bank switching the RAM.
I use Arduino Mega as system controller, to preload ROM image into SRAM (with Z80 in BUSRQ state), before letting Z80 to start.
So, need no ROM, yet.
Z80-MCB2 uses similar method start-up method.
Wow, man does that take me back! I cut my teeth on the Commodore C=128. I had just become disabled, and about a year before had purchased a 128 for my kids. Well the 128 became my entertainment system as the doctors worked on getting me back on my feet following a line of duty accident while working on the police force. The Commodore came with an extensive book on how to program with BASIC, and with nothing on the TV but soap operas during the day, I found myself teaching myself basic. Soon it became known that I knew about computers and folks with every sort of PC were calling me to come to their businesses and work on their early computer systems. Most were old IBM machines as well as the occasional Compaq running CPM so I learned those Operating systems as well. Now I play with micro controllers as I am not that far behind you in our hobby. Thanks for the great videos! They expand my learning from long, long ago.
Awesome! Glad you enjoyed them. More videos to come, at the pace of it being a hobby. :)
Randomly came across your channel in my recommended feed and have really enjoyed the couple of videos I've watched so far. Subscribed and looking forward to seeing more. Cheers!
UA-cam recommended this video to me today. As a Z80 fanboy, ZX81 and Amstrad CPC464 owner.
Very good. Back in the early 80s I was doing something similar with the 6502. At that time the smaller capacity 6116 ( 2k x 8 bit ) sram was more affordable. But my application was embedded inside medical instrumentation, so one 6116 and a 2764 EPROM was enough
12V for programming? I remember when it was 25V.
I built a programmer that worked with an Acorn Atom in the school computer class, the thing was entirely software driven, having the 8 bit data from the user port and 3 lines from the printer port (reset counter, step counter, program pulse). The programming mode was armed by a switch on the unit which engaged the VPP supply - a really weird setup that used a 6-0-6V transformer driving a bridge rectifier from half of it and a voltage doubler from the whole, adapted from a circuit I found for producing a parasitic negative rail with a FULL BRIDGE RECTIFIER providing positive
Did it get used for nefarious purposes? Of course!
Damn you're old
As even 512KB SRAMs are dirt cheap these days (AS6C4008 5V 32 pin PDIPs are sub $7 in lots of 1) then you might as well add a little extra hardware and use bank switching.
The 27C256 without the window is still an an EPROM, same as the 27C256 with the window (except no way to erase it). The windowless version is referred to as OTP - one time programmable. They were cheaper than the erasable versions. The ones I had at work were plastic packages rather than the ceramic packages of the windowed chips.
Weird that this has popped into my feed lately, but I like it. :)
Also, another possibility for a ton of storage is the M-Systems DiskOnChip 2000. It comes in the 32pin (sorta) standard JEDEC pinout and is mapped into 8k of address space. They're usually used in PC/XT's for solid state storage, but I have seen them used in embedded MIPS/Power architecture machines. They are 8bit, so there's no reason they can't be used in Z80, 68k, etc.
Just binge watched the z80 series... well done and fun. If you ever create more i will watch! Liked and subscribed...
Memories of my days in college as an EE major. Stumbled upon your channel, great stuff.
Some of the PROM chips with no window are EEPROM chips. Where you can reprogram with a programmer.
Yes, but it's all in the part number. 27 series with no window are OTP, but 28, 29 or 39 series are reprogrammable.
My Z80 computer uses a 128KB Flash ROM, the SST39SF010, like all of my 8-bit computers. I guess I'm just different. However, I can use jumpers to select between 8 different programs from the same chip, which is pretty cool.
On my Z80 Playground system the options I went for are 64K ram with 32k rom overlaying part of the ram. You can then switch the rom on/off from software. I think this gives the best range of options, as you can copy part of the rom into ram then turn the rom off. You can see it here: ua-cam.com/video/y9HNbJzdbpE/v-deo.html
Yeah! I've been enjoying your video series and always looking forward to the next one. :)
On my selfmade Z80 I used M28F101 FlashROM and MCM6206DP20 SRAM, both from scrap computers.
That was back in year 2000. Too bad, on todays scrap computers you will never get components like this.
A GALLON of EPROMS! 🤣 That's what I call thinking *_BIG_*
This is really useful info. I should have watched this before purchasing the wrong chip for my project.
Ah bummer! What did you buy vs now realize you should have gotten?
@@KennethFinnegan I originally purchased an AT27C256R but then realised it was 1 time programmable. I also think it might need a 12V supply for programming. So I've now got an AT28C256 which I believe can be re-programmed multiple times and only requires a single 5V supply. I'm still uncertain about this stuff and have not used either chip yet. But it is the next job on my list.
Yes. The 27C256 chips that don't have a UV window are one time programmable. 28 series can be erased electrically and reprogrammed.
If you don't have old chips to start from, the 32-pin flash chips are a good way to go. Cheap and lots of capacity. Nearly the same pinout as the 28 series EEPROMs
I've been looking for my "perfect" hobby computer. I can't really decide if I want Z80 or 6502 based CPU. I built Ben Eater's kit, but got tired of futzing with the breadboard connections. Removing the ROM over and over again to program would pull some address lines. I just want a simple computer that I can hold in my head while programming.
Eventually, I'll learn enough KiCAD to design my own with a ZIF socket for ROM and maybe a built-in max232 so I can just plug in a usb cable for power and comms. Maybe the RC2014 would do for my wants/needs but, I'm not really interested in running retro software so the memory map doesn't need to match old systems. Z80 is interesting because there are models that run 20MHz and I/O isn't necessarily mapped into memory space.
I have a couple of EPROMs and I wanted to erase them, but I don't own an eraser for them. I don't really plan on getting any more since the flash chips and eeprom chips with the same pinout are usually cheaper, so I left them on the deck in the sun for two days. No bit flips, all the data is still there...
If the Zilog Z800 had been used as the default chip for all home personal computers then maybe they might have been on a power with the likes of Motorola 68000 with the ability to do multiply and divide without having to reinvent the wheel.
i'm using an Arduino Nano instead of an EEPROM for my Z80 project. Problem I had had is, the Arduino is not a tri-state device. The digital pins behave OK input mode, but the analog pins still draw too much current in input mode and therefore kept pulling my data bus down. I found a 74LS245 bus transceiver didnt work satisfactory, but 74ls241 buffer does enable me to bridge the Arduino Nano to the data bus.
Bonus for using the Arduino Nano is, My "ROM" emulator code can also disassemble on the fly, which has been amazing for debugging (helped by M1 signal)
This is limited to 512 bytes of address space for Z80 code on the Arduino, but my Z80 assembly coding is pretty awful and I havent written a program that big yet lol
Yea giving me 70'80' flash backs..
I had fun with a Z8 chip which has onboard Basic. For memory I use a 32 kB SRAM that was wired to appear as ROM in the lower 32 K and as RAM in the upper 32 K.
Unfortunately the breadboard wiring put too much of a capacitive load onto the Z8 and it overheated and failed. Were I to experiment again I would devise a PCB, not use a breadboard.
We aren't in the early 80s anymore...Music was great but electronics cost a fortune. :(
OOO.... BRB busting out my Queensryche...
one problem with uv eproms, especially lower capacity and 'older' type numbers is they need fairly high voltage to program, and many modern programmers cant do them ... and not all of a particular type number are the same , some manufacturers may use different programming voltages to others...
A trip down Memory Lane.
I use EEPROMs as they're simpler to reprogram. So I am curious why you use EPROMs, is their an advantage over EEPROMs? Edit: Never mind, you addressed it at the end of the video.
Kenneth, I have a question about the Qi receiver you built. The question is connecting this to a lithium ion battery to charge and to power a device.
I'm more wondering why you asked this question on a totally different video.
Great video. Super useful.
You know, if you put a battery on the power pins of one of those 64k byte chips it becomes a permanent memory device (as long as the battery holds out). Write whatever "ROM" code you want to it and use the rest of it for RAM. Suddenly you have a full compliment of memory (both "ROM" and RAM) in one chip. Yeah it will take a bit of finagling with the power pin. But so what. A simple diode to keep it from feeding the rest of the circuit usually works. Play with it.
Is there a single chip solution that read and writs like ram but also holds its memory?
bettery backed stuff makes me iffy. a z80 board with a single mem chip
Not sure if it exists but a chip with 8K ROM (erasable) and 56K RAM in 1 chip would be nice to cut down on components and wiring. Maybe only suitable for hobbyists so not economically viable.
Or other combinations like 16/48 etc.
Hmm, I thought you might have covered pagable memory. Way back in the day I had I think it was a TRS-80 Model IV that had 128K of memory and I seem to remember that it could legally or by hack was expandable to 265K. This was before the IBM PC's really were released. Mine was 64k on board but if paging was enabled and the address pointer was pointing to C000-FFFF it would use whatever was in the D-Latch. So even though it was 16-bit addressing for the CPU it could be tricked to use 20-bit addressing by a hardware trick. But you only could access it in 16k pages. Most of the time it was some sort of data as you couldn't point a program counter to it and think it would work but I guess if you were careful in it's design that would be possible as well. The problem that would have to be solved is that's where CPM placed it's kernel was in the upper memory space so you would have to move it in memory so it wouldn't cause a problem.
For ROM options, what are your thoughts on 39SF series? Prices look good and they follow similar pinouts.
Never heard of it. It seems to be a variant of 29F series flash? And yeah, 29 series is a perfectly valid choice that I just didnt happen to cover in this video. Particularly handy when you want to be able to save back to the chip on a running system. I'm tinkering with a 29C010 chip to see if I can get it working as persistent storage for this computer.
@@KennethFinnegan well, 39SF is still manufactured, and can be purchased on DigiKey for under $2. As of "storage", you could play the NES trick and just use 6264 RAM with a simple 3.3V lithium battery to hold it up. That's how Legend of Zelda, for example, worked.
I use 39 series ROMs in my projects. They are quite cheap for a lot of bits, even if you don't need to use them all - just tie the unused address lines low, or to some headers or other logic for banking/paging.
I've also got a collection of 27 series with windows that I have pulled from electronics over the years, but no eraser (yet). I may get one in the future if I want a really retro look for one of my projects, but for now I consider them a bit of a faff.
so: prom = program once and it now is rom
eprom = use uv light to erase then can be reprogrammed
eeprom = you can use electricity to erase and then you can reprogram
i get that right? 0:-)
You got it!
Is there a fully static core version of the Z80? I wanted very much to do some Z80 projects but I had to switch to 6502 which seems to perform well at very low clock speeds, while the Z80 became unstable.
Wish this video was around a few years ago when I attempted to build a Breadboard Computer.
Use X-Ray to erase windowless EPROMs
Think of all that data you’ve erased. The data archivist in me is crying! /j
Which data? On the ROMs I pulled from e-waste?
Yes. That’s the joke. You know some poor bastard needs rom 3 of 6 to get his gear running. And you erased it! Lol!!
I like your vids. You were a YT random for me, now I’m here. Thank the Google.
Haha. Fair. Pretty much all of them came from work, and I don't think they would have appreciated me posting ROMs online for prototype builds from the 90s. Glad you're enjoying it here! :)
Curious if that's a static-safe surface. I used to think it didn't matter until I did RAM tests :(
Given the stakes here, it does not matter. I'm enjoying myself playing with chips I got out the e-waste.
@@KennethFinnegan Yeah, i still have a big box of cache chips from broken motherboards.
i havent blown any chips due to static ....yet...... worst thing is when you buy them and they arrive stuffed in a bit of polysytrene, instead of something reasonably antistatic ...
Don't bother with 8kB of SRAM, you can get 64kB SRAM on ebay and pretty cheap too.
Next step: Bank switching and adding even more RAM
Yeah. Depends on your needs for the project, but the main thing is to appreciate that all of these SRAMs are about the same price, so no point in using multiple lower density chips to save money like many of the original designs recommend. If you want 64k of RAM, get a 64kB chip.
I just didn't happen to have any 64kB wide DIP SRAMs, which is why I showed an 8kB SRAM. I haven't happened to buy any of this; all from e-waste.
There are even 611024 chips in existence. ;)