N8VEM SBC V2 – Still awaiting shipment

Well, Mouser managed to send an email today letting me know that they have shipped my package which has the needed parts to get this board up and running. However, it looks like the package will not get to me until 1/13/18 (4 more days).  Even though I am only 4:30hrs away from their warehouse.  I’m going to be honest, I’m not very happy with their service this time around.  But I suppose every company is allowed to have a bad day from time to time…

I already have all of the sockets and passive components soldered. I’m just waiting on the chips to stick into the sockets.  As well as an oscillator. I plan on testing this board at 16mhz , but may drop the speed depending on how the initial testing goes.  I decided to go with ACT logic families, since they have a very fast propagation delay, low power consumption, and are CMOS and TTL compatible.

The bare SBC V2 Board

Missing only the chips, the CPU Clock, and a 1k resistor array (RR1).  Well, and it needs a bi-color LED…

I actually had several of the chips needed on hand.  The board currently has a 20mhz CPU (z80 of course), an 8255, an 16C550, and a MAX232CPE.  But I still need to have a few more ICs before this will be able to boot to CP/M.  Still waiting on Mouser…

As you may have noticed in the second picture above, I installed a machine pin DIP-8 socket in place of P4 (CPU Clock).  This allows me to try a variety of oscillators until I find one that works as desired.  The goal is to have a very fast processor, and be able to run the SCG (Sprints and Color Graphics) Card in this computer.  Though I hear that card prefers something in the range of 4mhz.  For some reason I have to believe it can handle more speed.  Maybe the person who suggest this used a slower logic family???

As soon as I have more to report I’ll be back with another post.

2nd Batch of Counterfeit GAL22V10s??? Or not???

Well, I discovered a package in the post today.  This time an order of GAL22V10B.  Upon opening the package I took note of how good the condition of the ICs were in comparison to the previous batches I have ordered in the past.  These really do look to be in good shape.  However, there are obvious signs that they have been previously used.  Such as slight wear on the pins.

But will they program, that is the question.  Well, I am here to tell you that the answer is…..  Nope, I couldn’t get so lucky.  I have only tried 10 or the 50 that I ordered, but I will tell you this, with this many that are bad I can’t see many of the others working.

So this brings me to my next question.  Why am I having so many problems with these PLDs???  Is it my programmer?  It’s worked fine on 16v8s and other 22v10s for some time.  But I have run into the problem before.  See the picture below:

I have run into this several years ago, and actually posted about it over on AtariAge, here is that post.  It’s mentioned in post #11.  And it’s the same problem we see here.  So that begs the question, are these “Re-Caps” that have been labeled as ‘GAL’ when they may actually be ATF22V10s???  That would explain the problem programming (Atmel variants use a different algorithm to program the PLD, but the JEDECs are compatible from my understanding).  But that is just speculation.

If anyone can shed light on this, I’d love to hear from you.  I’ve got about a dozen dozen of these things that are refusing to program that I’d love to salvage considering that they cost about a $1-3 depending on where you buy them.  But for now I am just assuming they’ve been programmed too many times.  The funny part is that they verify as blank…I’m wondering if they were erased and the lockbit was set?  Although I’m not sure that would make a difference….

If you’re interested to know where I got them, here is the eBay link:


Now here is another interesting bit, there are several feedbacks for this item from this seller, stating that everything was as it should be.  And the listing says that they’re 100% tested and working.  So now I have to wonder, is it the chips, or is it my programmer???

5v to 3.3v Logic Level Shifting Made Simple

When I first started playing around with electronics I was like the other 90% of people to do so.  I started by playing around with micro controllers and other simple items.  And while I had no idea what I was really doing for a long time, there was one thing I learned very early on.  And that is that level shifting is not only often a requirement, but is often confusing to the beginner.

Often a beginner needs to create a 3.3v signal from a 5v signal.  Ok, so you use a voltage divider.  No problem.  But what if you need to create a 5v signal from a 3.3v signal?  Well, then you get dozens of homebrewed circuits often times taking 2-4 resistors, a diode or more, or maybe transistors to invert logic.  It gets confusing.  And for someone needing to learn the basics, that is not a good thing.

Even after I had learned a lot about electronics I still struggled with what the best way to convert between voltage levels was.  90% of what I needed to do was based on 3.3v and 5v logic.  So I knew that I could narrow down my requirements to being simple, requiring very few components, and being easy to understand.  And that is when I discovered the 74LS07 IC.

The 74LS07 is an Open Collector Buffer.  Meaning that the buffer’s output has two logic levels.  And that is not 1 and 0.  No, instead it is High-Z or 0.  Meaning that it’s out put is either high impedance (meaning not connected to anything), or it is equal to ground.  What that means is that we can use a pull-up resistor to tie the output to whatever level it is that we want within the specifications of the part.  See the truth table here:

Great, so we can easily convert to 3.3v from 5v, but we still have to convert from 5v to 3.3v!  Well, that is taken care of in this design as well.  You see, the inputs on the LS07 accept input levels as low as 2v!!!  Thats right 2v inputs are able to activate the output!!!  Check out the recommended specs, here:

So that means that we can reverse the design to create a 3.3v signal from a 5v signal.  See the examples below.

Now, how does this work?  Well take a look at Texas Instrument’s Official circuit for each of the 6 buffers in a 74LS07.

Let me guess, if you’re a beginner you don’t understand what is going on, right?  Well, lets simplify this for you (keep in mind, this is just to give you an idea of what is essentially happening).

You see, a PNP transistor such as this would only “turn on” when the input is not receiving any current.  So, we can think of this for demonstration purposes as 0v.  And we can think of it as 5v when the transistor is “turned off”.  So when the input is at 5v, the out put is Hi-Z (or left floating if you will).  When the input is at 0v, the output shorts to ground through the transistor making the output 0v.

So by using a pullup resistor to bring the output to the desired output, we have now crafted a level shifter.  And per the datasheet, we can have output voltages as high as 30v!  I’m not sure what the maximum input voltage level is, as it is outside of what my needs are.  And I’m too lazy to look at the datasheet.  But I’m guessing it is a little above VCC at the minimum.

The simple use of this one IC and a few resistors completely takes care of most peoples needs for logic shifting!

But why use this rather than voltage dividers and the diode circuits?  Well, that is an easy question to answer.  Most of those circuits are SLOW.  And by that I mean that the rise and falling edges of the signal may work for some applications when they will not even come close to others.  Not to mention they can become inefficient and consume quite a bit of current.  But since this circuit is purpose built, the power consumption is lowered. And with the use of low value resistors we can increase the spead of the rise time of the signal (the falling edge speed is essentially TTL speed).

That means we have a circuit that uses less power, is faster, and uses less parts than the other options.  Sounds like a win/win to me.

The Quest for More

Prototyping has begun.  Working up a standard for using an SD Card is the end goal.  But not just that.  I actually have some other plans for a “project” to go along side the SD card.  Not something that will be added to the overall computer.  Rather something that will just be a fun project FOR the computer.

But to do this, I need more I/O.  A lot more.  Because of this I decided to add another 8255 PIO and a z80 PIO.  The latter for it’s Mode 3 operation which will come in very handy with the SD card.  Also, since we will be doing file handling routines, it might make sense to have a RTC so that we can determine the the current time.  I had several ICM7170s on hand, and with the addition of a watch crystal and a coin cell, I should be able to rig it to work.

Progress is still a little slow due to work, but updates will be posted regularly.   As progress is made, that is.

Also, changes have been made to the Product Pages for the G80-S computer to reflect some needed information.  And a download page for the software will be added shortly.  I ask that if any bugs are discovered that they be reported, and I will issue a patched version.

Do you have a project that you used the G80-S or the TinyBASIC 2.5g software for?  Shoot me an email.  I’d like to get a picture, and possibly do a write up about your project.  Better yet, shoot a video, and I’ll add it to the blog crediting you! (With your permission of course).

Got a Website centered around vintage technology, software, or other hardware projects?  Shoot me an email, with your website address.   I’ll add it to an upcoming “Links” page.

Studying for Mass Storage…

Now that TB 2.5g and G-DOS 0.50b are finalized and out there in the wild, it’s time to turn our focus to Mass Storage.  That’s right, we need to be able to add, remove, modify, and use files contained in some type of file system.  The type of file system may be up for debate.  But regardless of what we decide to do with this computer, we need a way to access binary files, BASIC programs, etc.

So the two main types of file systems of interest to us would be FAT or a CP/M file structure.  Considering that this computer only has 32k of RAM, that dissolves any idea of using CP/M without major modifications.  That’s another project for another day.  FAT on the other hand has several advantages.  Firstly, it is readily readable by a modern PC.  Which means that we should be able to write and transfer files between this computer and a PC with ease.  Secondly, it is highly documented.

Knowing this I set out to learn everything that I could about the hardware side of the SD format.  First thing I discovered is that there are two protocols for communicating with an SD card.  The first is SPI, a pretty straight forward protocol similar to what one would use with Serial Shift Registers. The second is SDIO, which is completely undocumented.  Knowing this I knew that I would be using SPI.  So I would need the following pins: Clock, MISO, MOSI, and Chip Select.  That is in addition to the 3.3v supply voltage.  Speaking of 3.3v, i would also need to level shift from 5v to 3.3v and vice versa.  Luckily I recently ordered 74LS07 Open Collector Buffers, so this is no problem.

But how would I drive these pins?  Well, that is when I began thinking about the onboard 8255 PIO.  Obviously it has plenty of pins…but I wanted to use that for general purpose I/0…  And besides, I do not want to dedicate one whole port to just one input pin!  But wait!  If I were to add a z80 PIO I could use it in Mode 3, or I/O mode!  That means I can specify in software whether a pin is input or output!  Fantastic, I have the hardware figured out.  Now onto the SD SPI Protocol.

And that is where I am at now.  Reading in the plethora of information available on the web, which doesn’t really give me much information about the hardware side (like do I write one byte, then read a byte? Or how do I specify where I want to read data from?).  That is until I found the resources below.  And while I am still trying to crawl through the information, I am taking many notes along the way.

If you’re interested in this type of stuff, I suggest giving it at least a once over.  You’ll probably learn something that is of no real use to you outside of this hobby.


Simple FAT and SD Tutorial Part 1

Simple FAT and SD Tutorial Part 2

Simple FAT and SD Tutorial Part 3

Simple FAT and SD Tutorial Part 4

Avaya ISAPC-00 ISA to PC Card Interface

While PC Cards (or PCMCIA Cards as they were mistakenly known) are a thing of the past, they can often be quite useful.  Take my Compaq SmartStation Laptop setup.  Being from the 486 era, and a laptop, there are not a lot of solutions for mass storage transfer.   There was no USB.  There are no commercially available adapters for installing a 5.25″ drive (although I made my own with my 3D printer).  The only solution you would normally have would be a Parallel Port Zip Drive.  But luckily for me, it does have two PC Card slots.  And since there now exists PC Card to CF Flash adapters, I have a solution for mass transfer.

But, in 1993, someone decided there was a need for a ISA to PC Card adapter.  In fact, there seems to be a few different controllers for them.  One of which is the controller in question here, the Vadem VG-469.  The other one, that I’m aware of, was made by Intel.  And is the basis for the Vadem product.

I believe this particular card, and others like it, were part of some industrial solution.  Someone needed interchangeability between a Laptop and a Desktop for their PC cards.  But the real reason I think this has to be an industrial design is due to the lack of drivers.  There seems to be enough information for a Windows 95 machine to use these controllers.  But not WFW 3.11, which would have been the default OS during the time this card was made.  Unless you were still primarily using DOS at the time (which there are also no drivers for).  That leads me to believe that it was likely for some other OS.  But that is speculation at best.  Maybe someone just needed a portable HDD, and this was the interface.  Thats right, PC Card HDD solutions did exist as well…

Whatever the case, it is an interesting piece of Tech History from the 1990s.  Check out the video below.  Enjoy.

G80-S Prototyping Boards Arrive!

Retro Depot is happy to announce that the G80-S prototyping boards have arrived. They’ll be added to the store in a day or two.

So far everything looks good. Although we would suggest that you use extra tall stackable headers. Otherwise clearance may be an issue. But your particular setup may give varying results.

These boards feature breakouts for both the z80 bus as well as the PIO ports, a location for a 1117 Regulator (for 3.3v source), power indicator LED, Micro SD location with breakout (including spots for 1208 capacitors), and just over 1000 pads in a standard .100” grid.

G80-S v1.0 PCBs Have Arrived!

Great news fans!  The PCBs have arrived, been tested, and passed!  That means that I’ll will be able to get them up on the store for sale very soon!  I know many of you are anxiously awaiting the availability of these boards.  I’m waiting on a shipment of capacitors and resistors.  That should be coming in the mail before too long.  But it does take time, and because of this, if you order one of the early boards, you may be forced to purchase without the capacitors/resistors (something I plan on offering free of charge with these boards).

If that is the case, they are easy to find.  They are SMD 0805 footprint.  100nF for the capacitors (total of 16), and 10k for the resistors (total of 6).  One could make through hole work in a pinch.  But the safe bet would be to wait until the caps/resistors are ready.  You’ll know as soon as I do.  In the mean time, here is the front and back of the boards.  You’re excited, admit it.   😉

Also, International Shipping rates have been added to the store.  It’s a 3 tier flat rate.  It seems that for anything under about 8oz I can ship it for about $15 USD.  Once you cross over to 9oz it goes up to about $24 USD.   Above that, it’s best to ask for a quote.  But if we’re talking about a couple of PCBs, I should be able to ship 2-4 for $15 USD (plus the cost of the boards).  If you have any questions, just ask.

G80-S v1.0 Boards In Production

That’s right boys and girls! The first production run of G80-S v1.0 board has been ordered, confirmed, and are currently in production.

Some of you may be wondering what changes were made between the Beta run and the v1.0 boards. Well, to answer that question, not many. Firstly, and the most important aspect, the IEI line has been fitted with a resistor to VCC. This will allow SIO/DART interrupts if desired. It doesn’t affect current G80-S software. The other changes were simply cosmetic changes to the silkscreen layer. Everything should look pretty now.

Once the boards arrive I’ll get them checked for issues, but the layout hasn’t changed. So the only issues, if any, should be cosmetic at this point. (I had put quite a bit of thought into the board when designing it).

Also, I have designed and ordered a first batch of prototyping boards for anyone who wants to tinker with other hardware. This board will have breakouts for both the z80 bus as well as the PIO pins.  And will have a place for a Micro-SD card and a 1117 3.3v regulator. These changes will simplify modification for CP/M or testing with other hardware by allowing the user a way to expand the board while keeping the same footprint.  With stackable headers you could add quite a few items to the computer.  Just food for thought.

Happy Computing!

Popular Request: Microphone Pop Filter

Well, after suggestions from several viewers on my YouTube channel concerning the issues with my microphone, I have decided to break down and buy an el-cheapo pop filter.  Nothing special, here is the one I decided to purchase:

Double Layer Studio Microphone Pop Filter

It’s nothing fancy, but hopefully it will work until I have a chance to do research and invest in an audio interface and better microphone.  We’ll see.  But the good news is that it should at least help!  So look forward to future “hopefully pop-free” videos.

And for the record, it has already been ordered.  Whether or not I can hold off until it arrives before shooting my next video, that is a question for another day.  Although I do have a video I am REALLY wanting to shoot before too long.  However I have to do a little more work to get ready for it.  Maybe I could stretch it out until this weekend?