Multi-BIOS 7800 feasibility?

[+x=usr(1536)]

Some time ago, in digging around A8 stuff, I ended up looking into 4-in-1 switchable OS boards.  Specifically, this one:

 

 

It struck me at the time that this should be doable on a 7800 as well.  There are definitely use cases (particularly in testing and/or development) where having four switchable onboard OSes would be handy, but it could also be used for starting a game if no cartridge is present, etc.

 

Any thoughts?

[Overange]

Great idea

 

This could done like the Region Mode switcher for the Sega Consoles, I modded this so pressing and holding down the an A8s Reset button it uses a Pic to switch the TKII Stereo on and off, whilst using the Power LED as a status Indicator.

 

In this instance you could hold down reset, wait for LED to flash, this in turn will select the Kernal, let go and system will restart into that mode.

 

Very much like this one for the C64

 

https://github.com/tebl/C64-Kernal-Switcher

 

Maybe this design could be rejigged for the 7800 or even other A8s?? 

 

 

 

 

 

 

[juansolo]

Should be easy to do as long as they're all of the the same type otherwise you'd have to move some jumpers at the same time. If they're all EPROMs it should be as simple as lifting the CS pin on each chip and running it through a switch to select the active ROM. I plan to do exactly that if I ever get hold of a Kiloparsec ROM and switch between that and the Asteroids one I already have in there.

 

It won't achieve much to be honest other than having a different game on boot as making a 7800 truly region switchable would be really complicated. Sure you can put the PAL/NTSC ROM which removes the NTSC region lock. But it doesn't make a NTSC machine PAL or vice versa and you will have compatability problems.

[+DrVenkman]

3 minutes ago, juansolo said:

But it doesn't make a NTSC machine PAL or vice versa and you will have compatability problems.

Yep. 

 

Effectively, a “BIOS switcher” for the 7800 would really only devolve to a way to boot with/without a built-in game, and potentially select among several built-in games or none at all. So kind of an internal multi-cart I guess?

 

Not a whole lot of point to it really, but since when has that stopped any true retro-hobbyist? 

[gambler172]

Well....my system can change its Bios easily.

Just plug out the actual Bios

and put in another one. Cause I got different

Bios from a former Atari Engineer.

I will show a picture during the next 

days.

[+x=usr(1536)]

10 hours ago, juansolo said:

It won't achieve much to be honest other than having a different game on boot as making a 7800 truly region switchable would be really complicated. Sure you can put the PAL/NTSC ROM which removes the NTSC region lock. But it doesn't make a NTSC machine PAL or vice versa and you will have compatability problems.

And that's a fair point.  I was pretty much just using it as an example, but you are correct in that if the hardware isn't there to support the scan type it's not going to work correctly.

10 hours ago, DrVenkman said:

Effectively, a “BIOS switcher” for the 7800 would really only devolve to a way to boot with/without a built-in game, and potentially select among several built-in games or none at all. So kind of an internal multi-cart I guess?

Ehh, dunno if I'd see it as 'devolving' necessarily, but your point is valid.  For the most part, I was looking at it from the, "hm, this looks doable..." standpoint and sort of letting what it gets used for be figured out as things go.  BIOSes were just what popped into my mind at first.

6 hours ago, gambler172 said:

Well....my system can change its Bios easily.

Just plug out the actual Bios

and put in another one. Cause I got different

Bios from a former Atari Engineer.

I will show a picture during the next 

days.

So, what are the differences between the two?

[alex_79]

17 hours ago, juansolo said:

If they're all EPROMs it should be as simple as lifting the CS pin on each chip and running it through a switch to select the active ROM.

Or just use a single larger eprom and switch the higher address pins.

[Stephen Moss]

17 hours ago, juansolo said:

If they're all EPROMs it should be as simple as lifting the CS pin on each chip and running it through a switch to select the active ROM.

Presumable you would be connecting all the all the I/O pin of the different BIOS chips in parallel, if so that would only reliabley work if the output pins of the deselcted ROMs are known to go to a tri-state condition when the ROM is deslected. Otherwise the deselected ROMs will be trying to drive the data lines either High or Low which would result in contention on the line when the active ROM tries to drive the line to the opposite state.

[juansolo]

Good point. I'll have to have a ponder.

[gambler172]

Here is mine. Easy to install and the different Bios s can be used

[+-^CrossBow^-]

11 minutes ago, gambler172 said:

Here is mine. Easy to install and the different Bios s can be used

I figured you were using a zif socket for this. But I believe the OP wants something fully self contained that can swap using a switch without opening the 7800 each time.

 

[gambler172]

12 minutes ago, -^CrossBow^- said:

I figured you were using a zif socket for this. But I believe the OP wants something fully self contained that can swap using a switch without opening the 7800 each time.

 

My 7800 is always open. 😉

[+x=usr(1536)]

Exhuming this thread because I ran across a case earlier today where being able to switch from the Kiloparsec BIOS I'm running to a stock OS ROM would have been extremely useful.

 

As mentioned, this 7800 has the Kiloparsec BIOS installed, which means that a) all 28 BIOS pins are available, b) the BIOS ROM is socketed, and c) there's a 74LS04 piggybacked onto the 74LS08 with attendant wire to pin 22 of the BIOS socket attached.

 

Is there anything in this configuration that may preclude a 4-in-1 OS board from working?  I'm guessing that there isn't, since the actual switching is handled on the 4-in-1 PCB.

 

Late edit: decided to just go ahead and order the @Mr Robot 4-in-1 PCBs; they should be here in about 2-3 weeks.  Got 10 each of the two different offsets:

 

[+bent_pin]

Were I doing this, I would use a ROM 4 times the size of the original, then use the highest 2 addressing pins to switch which BIOS was visible to the system. 

[+x=usr(1536)]

6 minutes ago, bent_pin said:

Were I doing this, I would use a ROM 4 times the size of the original, then use the highest 2 addressing pins to switch which BIOS was visible to the system. 

I'll know more when the boards arrive, but based on what I've read so far, using a 27c256 (32K) or 27c512 (64K) should allow for this to work.  27c256s seem to be thin on the ground right now, at least at a price I'm willing to pay for them, so chances are it'll be a 64K EPROM configuration.

 

Both ICs have two CE/CS pins.  The jumpers on the board control pin selection, permitting up to 4 BIOSes to be run from it.  In theory, it should also be possible to have a two-position jumper which would allow for two 32K BIOSes on a single EPROM, but that's getting ahead of things a bit.

 

The plan is to use a BCD switch to select the BIOS to use.  Power off, set the switch, power on, et voilà.  Should be pretty simple.

 

Before any of this happens, though, I need to replace my previous EPROM burner, which apparently disappeared the last time we moved house.  Probably going with something USB and minipro-compatible; don't want to throw a ton of cash at this since I'm just experimenting right now.

[+bent_pin]

15 minutes ago, x=usr(1536) said:

Before any of this happens, though, I need to replace my previous EPROM burner, which apparently disappeared the last time we moved house.  Probably going with something USB and minipro-compatible; don't want to throw a ton of cash at this since I'm just experimenting right now.

Got an arduino mega or due? You can whip one up on a breadboard in no time.

[+x=usr(1536)]

2 hours ago, bent_pin said:

Got an arduino mega or due? You can whip one up on a breadboard in no time.

Not anything I can free up; my wife used our last Arduino for I-can't-remember-what.  By the time I order one, it's getting up there in price near the lower-but-OK end of EPROM programmers.

 

What I'm looking at is one of these.  For what I need and want to do both now and in the future, it should be able to pay for itself in a reasonable amount of time.

[+bent_pin]

4 minutes ago, x=usr(1536) said:

Not anything I can free up; my wife used our last Arduino for I-can't-remember-what.  By the time I order one, it's getting up there in price near the lower-but-OK end of EPROM programmers.

I keep them in stock for my students and whatever projects that I'm working on. I have piles of them. That's cool that you and your wife share a hobby.

 

7 minutes ago, x=usr(1536) said:

What I'm looking at is one of these.  For what I need and want to do both now and in the future, it should be able to pay for itself in a reasonable amount of time.

That's a fine machine. You've given me some ideas to thing about for the hybrid machine.

[+x=usr(1536)]

10 minutes ago, bent_pin said:

I keep them in stock for my students and whatever projects that I'm working on. I have piles of them.

We typically have a couple laying around, but lack of availability in the recent past meant that neither one of us was doing the sorts of projects that needed them, so they never got replenished.

10 minutes ago, bent_pin said:

That's cool that you and your wife share a hobby.

It's more that we have interests that intersect at times   She's not as much into older hardware as I am, but has a background in BattleBots going back to when she was a teenager.  As a result, we tend to do similar stuff but in different ways or for different reasons.

10 minutes ago, bent_pin said:

That's a fine machine. You've given me some ideas to thing about for the hybrid machine.

Glad to hear it; I am buying semi-blind on this one having never used that specific model before and am going by what I've read in reviews (Amazon and elsewhere), watched in videos, and found in the way of software for it.  Still, it looks like a good bet - lots of flexibility at a reasonable price.  Exactly what's needed for getting back into the saddle.

[+bent_pin]

1 hour ago, x=usr(1536) said:

Glad to hear it; I am buying semi-blind on this one having never used that specific model before and am going by what I've read in reviews (Amazon and elsewhere), watched in videos, and found in the way of software for it.  Still, it looks like a good bet - lots of flexibility at a reasonable price.  Exactly what's needed for getting back into the saddle.

You'll be happy with that one.

 

1 hour ago, x=usr(1536) said:

We typically have a couple laying around, but lack of availability in the recent past meant that neither one of us was doing the sorts of projects that needed them, so they never got replenished.

I will take an inventory in the next few weeks, and if you'd like I'll be happy to sell you a box full.

[juansolo]

Finally got an EPROM programmer so it'd have been rude not to have done this. Got the PAL/NTSC Asteroids BIOS and the Open Kiloparsec BIOS on there. Slide switch to flip between the two.