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Messages - dangerman

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Interface / Re: Internal memory expansion
« on: 2020.September.16. 10:34:15 »
Unfortunately, I was too optimistic about EXP2. I can close the top, but it bends the plastic out about 1mm.

Yes - I found that out the hard way too :(

Btw., I was not able to use a standard double-row header on EXP1. It seems the distance between the two rows is off. I used two single rows instead.

I had forgotten this, but I remember having a slight problem too! I seem to recall that the official boards in the EP128 are directly attached by 28 individual tall pins, so for them the off-spacing wasn't a problem.

Hardware / Re: Enterprise Deployment Attempt Over FPGA.
« on: 2020.September.12. 11:19:17 »
Well I just wired the VSYNC interrupts directly to the INT signal of the CPU, but I guess it's not correct. I'm not sure about how interrupts work in general. I have read about Dave's registers, but I am not sure how they work. For example, what is connected to INT1 or INT2?

On the Enterprise, interrupts are connected to the DAVE chip and then DAVE controls the INT signal of the CPU. Interrupts are latched by DAVE so they can get passed to the CPU (eventually) even if they occur when Z80 interrupts are temporarily disabled.

DAVE has 4 sources of interrupts...

1. Variable frequency interrupt - either 50Hz, 1kHz or a variable frequency specified by the tone generator (ie the pitch of sound)
2. An interrupt at 1Hz
3. INT1 - this is connected to the Nick chip interrupt
4. INT2 - I think this is connected to the network port, so you probably don't need to worry about it.

You can find out what interrupts have occurred by reading DAVE register $B4.
You enable/disable the different interrupt sources and clear interrupt latches by writing to DAVE register $B4.

Hardware / Re: Enterprise Deployment Attempt Over FPGA.
« on: 2020.September.12. 11:00:49 »
as i saw Nick interrupt is on int1, and nothing on int2

It's been a while but I seem to remember that int2 is connected to the network port, so that networked Enterprises can be alerted if another machine is sending data.

Interface / Re: Internal memory expansion
« on: 2020.September.12. 10:54:00 »
Awesome news :smt041

I agree with Pear. The input voltage to the regulator 78L12 is too low, so I'd try replacing TR2

Interface / Re: Internal memory expansion
« on: 2020.August.30. 16:47:08 »
One thing I've not yet understood is how the Enterprise senses the amount of RAM available. Does it probe memory on startup or is there logic in the RAM expansion to indicate how much RAM is present?

At startup, the EXOS ROM tries writing to each segment to check if there is RAM there. The hardware doesn't provide any extra information, it's tested by software.

Interface / Re: Internal memory expansion
« on: 2020.August.29. 17:43:54 »
Excellent work. :smt041

Btw, what program did you use to do the design?

My first instinct would be the two voltage regulators (7805) to see if the machine is getting enough power. They are however fine. The next would be to recap the machine. Capacitors does not age well.

If the 5V is fine, have you got a volt meter and checked the 12V coming out of the 78L12 regulator? It could be that you're not getting 12V to the motherboard. Apparently the most common fix with 12V is to replace TR2 and C9.

Interface / Re: Internal memory expansion
« on: 2020.August.29. 10:42:08 »
I've been looking at this all day, and I'm afraid that I can't find any way to add that PDIP socket for the FLASH chip, and still end up with any kind of sensible board layout.

If you're going to program the chip in situ on the actual Enterprise, then you can still use the trick of swapping the order of address lines and data lines.

But maybe it's still too complicated to add the FLASH.

Interface / Re: Internal memory expansion
« on: 2020.August.24. 21:18:27 »
Thanks for the info. Starts to make sense now.

Good luck with adding the Flash ROM. I expect you know already but the original EXOS will only find ROMs in segments which are multiples of 16. So you'll need Zozosoft's unofficial EXOS upgrade to recognise system ROMs that don't start on 256k boundaries. 

Interface / Re: Internal memory expansion
« on: 2020.August.24. 11:35:35 »
Wow - great work! :smt041 Not worrying about the order of the address and data lines makes life much easier doesn't it?

I'm afraid I'm not good enough at electronics to reliably check it. Although I do have a question for my own learning if that's okay. Why are there 3 capacitors? When I designed my [amateur] expansion I just had one capacitor to smooth the supply to the 512k chip. So it turns out I should have put one on the ATF16V8 as well. But why the 3rd capacitor?

Basically I didn't really know what I was doing and was amazed that what I did worked at all. :)

Hardware / Re: SymbiFace3 is near your Enterprise...
« on: 2020.August.13. 23:13:39 »
FYI... EXOS, EXDOS and Cyrus Chess also write to their own ROM! :roll: :twisted:

Was Cyrus Chess officially made as a ROM? I always assumed the ROM version was a hacked version of the cassette :?:

Interface / Re: Internal memory expansion
« on: 2020.August.13. 22:12:30 »
but honestly, both the Lattice and Atmel GALs have a 20 year rating for the programming, and I really don't like the idea of a new memory expansion board on a 35 year old computer having a built-in time limit that will eventually cause the board to fail.

Yes, I'd forgotten about the time limit. That would be very annoying indeed. You make a good case for using standard parts.

Interface / Re: Internal memory expansion
« on: 2020.August.10. 11:41:08 »
Don't follow this if you later want to add some FlashRom to your expansion.

Good point about the FlashRom - that wouldn't work with my home-made expansions!  I guess it all depends how easy you want the routing on your memory expansion to be ;-)

Other 5V GALs, such as Atmel's ATF16V8B, are still widely available and affordable, but then that would be a change in Saint's design, and I don't know if that would work.

Then, whichever GAL is used, someone has to have the right equipment, and then take the time, to program it.

Do we know what GAL Saint used? Pinouts are often pretty standard so Atmel's ATF16V8B might just be a drop in replacement.

Alternatively if you were making a new board, I believe many circuit manufacturers will programme the GALs for you when get the board made up. (Although I don't know what that does to the cost and IMHO, there's nothing wrong with your 74HCT138 idea.)

Incidentally, the ATF16V8B is exactly the one that I used in my internal memory expansion. They're very easy to program using cheap universal programmers.

Interface / Re: Internal memory expansion
« on: 2020.August.10. 11:18:12 »
I think a simple external RAM expansion connected to the right side port of the computer would be nice as well, without needing to solder and modify the original HW.

Sadly, the problem with an external RAM expansion (and why I decided to build an internal one as well) is that you need some kind of bus board or pass-through to connect an EXDOS as well. Maybe it doesn't matter if you have the cartridge SD card reader, but I can see why some people would prefer to solder something internally instead.

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