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.

Contemplating Graphics

I’ve been thinking about graphics the last week or two. One of the items on my list of things to do is to build a video board for the G80-S. However, graphics pose a new problem…

Video Processors of the time period that this computer would exist were very primitive in respect to their capabilities. Wanting to have a machine similar in capabilities to an MSX, this requires me to use a chip compatible with the TMS9918A. The problem with this chip is that it doesn’t have the greatest of text modes. 40×25 characters just doesn’t work for the Monitor program, or any future aspirations of CP/M or DOS, which typically require 80×24 or 80×25 text modes.

There is a solution to this. Grant Searle’s adaptation of Daryl Rictor’s AVR video processor to 80-column text Mode is perfect for CP/M or DOS. But the problem is that: 1) It’s not compatible with the TMs9918A graphics, 2) the graphics mode leaves quite a bit to be desired.

That leaves me contemplating what should be done. I’ve got some ideas, but I figured in the mean time I would play around with a few different projects, at least until my new boards come…

One of the things that I’ve been wanting to play with was a 128*64 pixel graphics display. I bought one off of eBay a while back, and I’ve never toyed with it. 128*64 pixels isn’t a lot to work with. But I figured I should at least be able to get the G80-S to utilize it for it’s display…at least for TinyBASIC. I’d like to have 32-columns at the minimum. At 8-rows that should give a decent display. But cramming 32 characters in a 128 pixel wide display is a chore.

But with luck I came up with what I though would be a decent character set. I’ve attached the images below for your critique. The characters are 4×8 (width x height). That should allow for a 32×8 display and still permit normal graphics. Now I just have to write some code to test it.




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!

TinyBASIC: Variables, Memory, and Expansion

In my last blog post I shared that I have managed to integrate TinyBASIC into my monitor for the G80-S in a ‘mostly stable’ way. Now that has progressed from mostly stable to very stable. But further, the IN instruction has been revised to use variables. Which is quite handy, as it allows the programmer to not only write to I/O, but to also read from it, and make branches in his/her program as a result of those reads.

This is a big step, as it is the basis for other routines that can expand on the original TinyBASIC source code. Routines such as PEEK or POKE may need to use variables, and the ability to use variables to OUT to I/O is also important from a programmers viewpoint. And these routines just simply were not included in the original source, and I desire to have them available in my software. So as such, I’m further modifying TinyBASIC as I see fit.  And yes, when it is done I will release it into the wild.

Variables in TinyBASIC are straight forward once you understand them. To read from or write to a variable one simple needs to understand that they are nothing more than a predefined area of memory, and that they have a given structure.

This area of memory is defined as VARBGN in the TinyBASIC source. And in my personal example of code resides in 55 bytes of data starting from 0xFF00. Now, each variable is broken into two (2) bytes. However, they are not organized as you would assume, with the MSB being first, and the LSB being second (i.e. the way one would read the memory if layed out in from of him). No, TinyBASIC addresses variables just like the z80 addresses memory. I.e. if we refer to location FF88 in memory it will be listed as 88FF. Likewise, if we refer to a variable (for the sake of examples let say it is listed as 01h) in memory, it will be addressed like this:  01h 00h.  Strange, but ok.

Further, the first address of the variables is not ‘A’. I believe that it is ‘@‘ which I also believe is a pointer. But I have not confirmed this. One step at a time…

Now, this means that if we want to use variables it is as simple as figuring out which variable we want to use, and reading from or writing to that area of memory. Simple right!

As a result I have rewritten the IN instruction so that it now operates as a tool for loading a given variable for use by the program. It can be used in the following ways:

IN hh V
IN hh,V
IN hh=V
IN hhV

Where ‘hh’ is the port to write to in Hexadecimal, and V is the Variable ranging from ‘A’ to ‘Z’.

I’m still working on patching the OUT instruction to use variables. Sometimes the best way to solve a problem is to step back and let your eyes rest. And that is where I am at currently. I needed to step back until my eyes are fresh. But as of right now it can output a byte to a port.

The rest of the functions are still a work in progress. I have added a CLS function that can be used either direct or within code. I have also added a QUIT function which serves to exit TinyBASIC. So it is coming along.

Overall, my work on expanding TinyBASIC to be more usable, while maintaining a small foorprint, is progressing at a pleasing rate. And while this project centered around my G80-S computer, need is the mother of invention.  And as a result I will release the source once I decide that it is complete enough for release.

But for now, I leave you curious…

Integration of TinyBASIC

It’s been a productive weekend!   I’ve been able to integrate TinyBASIC into the monitor program.  Btw, if case you were wondering why the monitor states that it is G-DOS, it is motivation (and my intent) to integrate a FAT file system into the computer.  Likely using a SD card.  I’m currently working on the design.

But wait!  Integrating TinyBASIC into my monitor program is not all that I’ve done!  I’ve also been working on expanding TinyBASIC with the following items: IN, OUT, PEEK, POKE, and CALL.  That’s right, TinyBASIC will actually have some use other than just printing to the screen.  This will be a great tool for testing hardware designs.

As it is right now, I’ve added the IN and OUT routines.  OUT performs exactly how you’d expect:  ‘OUT NN NN’ where NN is a two digit hexadecimal number.  IN on the other hand I’m still working on.  The routine itself works, but I’m unsure how to finish it off.  What I mean by that is that I need a way to be able to assign a variable, and I haven’t looked deep enough into the code to be able to determine how to do so at this time.  For now, it simply writes the value to a specific address in memory: 0x8015. Which required me toying with memory locations built into the original TinyBASIC source.

Once I can figure out how to assign a variable to the command, it will become much more useful.  And that same scheme can be applied to the PEEK command as well.  POKE on the other hand should be as straight forward as OUT.  And this gives TinyBASIC a new level of functionality, and no more limitations on variables, as you’d be able to access memory directly.

And the best thing about this is that I believe that after expanding TinyBASIC I can keep the entire ROM (including filesystem routines) under 8K. Currently with the Monitor and BASIC the ROM is just under 5K (5013 bytes). I do not see why I wouldn’t be able to keep the I/O routines for an SD card and the Filesystem routines under 3k.  And I should only need a few hundred more bytes for the additional commands.  Of course one must also take into consideration the ability to save files from BASIC and load them again.  Who knows, but 8k is my goal.  We’ll see how well we can accomplish this.

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?

TinyBASIC for the z80 – TinyBASIC 2.0g

In celebration of 41 years of Li-Chen Wang’s TinyBASIC (the original Open Source Operating System), and the fact my G80-S Computer needed a version of BASIC, I am proud to announce the z80 port of TinyBASIC.

Version 2.0g was derived from the original TinyBASIC 2.0 source.  The method of it’s conversion was thorough.  First the original source was compiled in 8080 mnemonics.  It was then disassembled, and compared to the original source.  It was then modified for the z80 Instruction Set.  And finally, streamlined in order to make it a little more portable.  The link to the download is below.

TinyBasic_2.0g

However, if you’d like the assembly file for the G80-S computer, here is the link to that source code.  Enjoy!

G80S_tinyBASIC_2_0g

G80-S Runs Microsoft Basic 4.7b (sort of…)

As a followup to my post on interrupts, I decided to have a go at modifying Grant Searle’s I/O routines for his 7-chip z80 Computer. After quite a bit of work, I had the routines in his handler changed to conform with his code (at least I think), and function as intended (at least as far as I was able to test).

The next task was to try it with his modified version of the Nascom Rom.  And, after splicing the code, I compiled and tested…..and tested…..and tested…..

Well, the short of it is that it kind of works.  The video above says it all.  The serial routines seem to work fine up until BASIC starts up.  And at that point, my serial routines work fine, but there is some disconnect with Grant’s code that either doesn’t like my own code, or is simply amiss.

The video really does say it all.  If anyone has any ideas, or has ported Grants work over to using either the DART or SIO, I’d love to see your code.  Help a brother out… But seriously, watch the video.  It’s hilarious….

On the Subject or Intereupts

Although I have learned a lot by designing my own z80 computer, I have yet to learn much about interrupts. It’s just not something that I initially saw a strong need for.

However, since I have been looking at porting other people’s code over to my system I have come to realize just how important other people see interrupts to be. In fact, from what I can tell,  more often than not this is the case. At least with the code I have examined.

This means, that if I am to port some of the code I would like to use, I need to learn about interrupts.

The first thing of note is the hardware situation. On my first run of boards, what I’m calling the Beta Boards, the IEI line on the DART was left disconnected/floating. As it turns out, this is a no-no. This pin is the Interrupt Enable Input. Meaning it’s the enable on the SIO for interrupts. Without a High signal on this pin, there are no interrupts. So, I’ve fixed this issue on my new design by adding a resistor between IEI and VCC, and I’ve used a bodge resistor as a solution on my Beta Board.

The second thing to note is the different types of interrupt modes on the z80. There are three: Mode 0, Mode 1, and Mode 2. From what I can tell, Mode 1 is the most straight forward. In this Mode a low on INT will call the z80 to perform a RST 38H instruction. Which is essentially the same thing as a CALL 0038H. However, in order to return from this instruction the system requires a RETI instruction. So keep that in mind.

Mode 2 is interesting because it allows you to jump to a specific routine pointed to by a reset vector. In this Mode the upper 8-bits of the address is held in a register. And the lower 8-bits is placed onto the data bus by the peripheral. Trying to understand this Mode almost caused my head to explode. A little complex for our needs.

Mode 0, as I understand it, is a reset mode that is designed to be compatible with the 8080. Where in the peripherals place data on the data bus. I’m not going to presume to understand anything about this Mode.

So therefore we’ll be using IM 1 where polling is not usable. But wait, what if we need multiple devices? Well, luckily there is a way around this. Although I suppose it could be a little slow. When the z80 receives an interrupt the routine checks all the peripherals before deciding how to react. Good thing our system clock is at 6mhz. We may even need a little more speed. But in the end, if we have to, we can always use IM 2.

Here is an example of working code of Interrupt Mode 0.  I found interrupts a little difficult to understand at first.  But hopefully a very simple example of an interrupt routine will be enough to help the beginner.

IM 1 Example

G80-S Micro Schematic and Source

I’ve been meaning to upload the source and the schematic for the G80-S Micro for some time now.  I just haven’t gotten around to it.  However, I had some time to do so this evening.  So attached here is the schematic, and the source code.  It’s the v0.25b version of the software.  Use them well.

Also, a link to the Source has been placed on the product’s page in the store for the Beta boards.  So if you want to buy a board, you can download the software there.  If you don’t want to buy a board, but want to play with my design, the schematic is here and the source as well.  Have fun!