Correct usage of VDP ports following the standard

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By gdx

Prophet (3023)

gdx's picture

12-06-2017, 10:11

Most cartridge games seems works without too much keyboard issues but this is not the case for games on floppy disks.

I think it is not good to promote the MA-20 and clones. The standard is not suitable for this type of extension. The idea of moving the Bios is not a good idea because the ROM also contains information about the keyboard, etc and can control specific hardware.

The standard should have kept the principle that stipulates that the Bios must necessarily be in the primary slot 0 or the secondary 0-0. This greatly simplifies the handling of the slot.

I don't understand the choices that have been made. For exemple the variable MNROM added at 0FCC1h in the table EXPTBL. They did not even think of adding a pointer to indicate the matrix of the keyboard nor move information about keyboard, clock and VDP ports should have been moved to system variables.

MSX were not thought to be upgrated by users. The MA-20 is just a gadget.

By sd_snatcher

Prophet (3068)

sd_snatcher's picture

12-06-2017, 16:12

Quote:

I think it is not good to promote the MA-20 and clones.

Sorry to disagree. I think it's up to the users to decide what's best for themselves.

Quote:

I don't understand the choices that have been made. For exemple the variable MNROM added at 0FCC1h in the table EXPTBL. They did not even think of adding a pointer to indicate the matrix of the keyboard nor move information about keyboard, clock and VDP ports should have been moved to system variables.

There are many choices that can be questioned, like:

- Why did they choose the Z80 instead of the i8088 that had a more promising future?
- Why did they choose to use the TMS9xx8 instead of ?
- Why did they added that waitstate in the M1 cycle, when no other Z80 computer had that anymore at that time?
- Why didn't they raised the clock or the minimum required RAM for the MSX2+?

I hear so much destructive criticism about the MSX platform that I wonder what is the motive for such people to keep such disgraceful machine around, without doing anything to improve.

Quote:

MSX were not thought to be upgrated by users.

You're entitled to your opinion. But the MSX I know was designed to be very flexible and expandable. It was *the* major differential of the platform against its competitors.

Quote:

The MA-20 is just a gadget.

Reality check: And what related to +30 years old computers isn't?

Curiously enough, I saw no hostile resistance with the release of many other extensions not related to the MSX spec (*1) than one that is 100% compliant. Can anyone rationally explain why some few are so vocal against standard MSX extensions?

*1: Franky, SN76489, RPi cartridges/adapters, just to name a few. And no, I don't have anything personal against those.

By Piter Punk

Master (202)

Piter Punk's picture

12-06-2017, 18:27

gdx wrote:

I think it is not good to promote the MA-20 and clones. The standard is not suitable for this type of extension. The idea of moving the Bios is not a good idea because the ROM also contains information about the keyboard, etc and can control specific hardware.
...
MSX were not thought to be upgrated by users. The MA-20 is just a gadget.

I can't agree with that. The standard have the provisioning to the alternate VDP and to change the BIOS address. So, it's clear that it was thought with this kind of upgrade in mind. And that strategy is used by MA-20 and by internal upgrades in machines with the VDP integrated in MSX Engine, which needs to use the alternate VDP ports.

I guess the alternate VDP ports are used by many 80 columns cards, too.

By Grauw

Ascended (8439)

Grauw's picture

13-06-2017, 10:39

sd_snatcher wrote:

Curiously enough, I saw no hostile resistance with the release of many other extensions not related to the MSX spec (*1) than one that is 100% compliant. Can anyone rationally explain why some few are so vocal against standard MSX extensions?

*1: Franky, SN76489, RPi cartridges/adapters, just to name a few. And no, I don't have anything personal against those

That is an easy one to answer; because it asks people to change their ways. And you know how well that sits with people. Especially among MSX users, who have resisted changing their ways for 30+ years! Big smile

I say, just release the hardware, if the user base grows enough then support will follow. And if an MSX2 title chooses not to support it, well then the user base is no bigger than it is today (shame missing out on those people though), and the users know that not having 100% compatibility is part of the fine print.

By msxholder

Champion (336)

msxholder's picture

12-06-2017, 22:48

There is a NTSC 80 collums (60 HERZ) cartridge in my collection.
But never tested it with the MA-20
Thank's never thought of that ! Gonna try it.

By gdx

Prophet (3023)

gdx's picture

13-06-2017, 03:17

You are right, the users decide indeed what's best for themselves. It is a good thing to make know the MA-20 (if we do not hide his defects) but I prefer to advise all MSX1 owner to keep it and take in addition an MSX2 if they desire. This is by far the best solution. It was the cas even when the MA-20 was released at the time.

sd_snatcher wrote:

You're entitled to your opinion. But the MSX I know was designed to be very flexible and expandable. It was *the* major differential of the platform against its competitors.

You are right but not for the case we are talking about.

sd_snatcher wrote:

Reality check: And what related to +30 years old computers isn't?

I mean it's that it's a gadget sold at the time. Now it's become a curiosity.

By ARTRAG

Enlighted (6242)

ARTRAG's picture

13-06-2017, 12:16

It would be fun to see how the ma-20 toy deals with rom replacement.
I see two options:
Or its rom assumes usual ports for audio, keyboard and other i/o devices, so it does not respect the msx standard,
or it does a multiple jump with slot swap back and forth for any bios and isr call.
In the former case the sacred standard would be violated and you could incurr in troubles with the machines that will be produced in the future (by unwise designers naturally).
In this latter case, as the original bios is called, compatibility is safe but you add a huge overhead to any single action involving the bios.
In both cases it is better to make clear to the potential users that they are going to waste their money if the purpose of their buy is anything different by collecting such a card

By Poltergeist

Champion (273)

Poltergeist's picture

13-06-2017, 16:45

We can all concentrate on the MA-20 (I wouldn't want to call it a toy or gadget, it's probably a fine piece of hardware, and had it's use back then) but although MSX is a standard. We've seen that between MSX1 machines (software which runs on the one MSX, but not on the other), and various MSX2 machines (in which the sony HB500 with three external slots comes to mind) there are also compatibility issues. We would accept that software did not always work, and go running another game from tape.

And true: most issues could have been solved if the software was written correctly. But still, it could be possible to keep to the MSX standard, and run into problems with an exotic or future MSX. If you relied heavily on the cassetteport with your MSX1 software, it would not work on Turbo-R...

I didn't think that was a big problem back then, so why should it now?

That being said: a gameengine which runs for certain on al targeted MSX computers would be great also. Maybe I can create something nice also

By Piter Punk

Master (202)

Piter Punk's picture

13-06-2017, 18:02

msxholder wrote:

There is a NTSC 80 collums (60 HERZ) cartridge in my collection.
But never tested it with the MA-20
Thank's never thought of that ! Gonna try it.

To do an MA-20 'like' upgrade. Your cartridge will need:

1. The V9938 video chip (some 80 columns cards used other video generators)
2. At least 64KB VRAM (the ones with V9938 sold in Brazil had only 16KB VRAM on-board)
3. Use the alternate video ports.

You will also need the MA-20 BIOS and the MSX2 sub-rom somewhere. Some (many?) 80-columns carts had a EPROM with an software inside. You can use this EPROM to store the MSX2 sub-rom. Any separated cartridge with the MA-20 BIOS should be OK. So, your MSX machine needs to have at least two external slots.

Luca's aproach to don't need the two external slots is to provide the BIOS+SUBROM+V9938 in a all-in-one cartridge, with an internal slot expander. The prototype pictures shows that he also provides an slot conector in the cart itself. So, in a machine with only one (primary) slot you can connect the MA-20 clone and still have one (secondary) slot available. In a machine with two slots you have a better yet situation, with two slots (one primary and one secondary available).

Again, you're talking as the MSX1->MSX2 upgrade was a new or an yet to do thing. But even in the MSX good times it was the most popular way to have a MSX2 in Brazil. To do it in Hotbit or Expert with discrete components was "easy", you can remove the MSX1 VDP and put the MSX2 VDP in the same ports.

But do this upgrade in Expert Plus/DD Plus you can't remove the MSX1 VDP, which is integrated in MSX Engine. So, the upgrade kits of the 90's for those machines already used the VDP alternate ports. And most japanese software worked fine.

By msxholder

Champion (336)

msxholder's picture

13-06-2017, 19:47

Piter Punk wrote etc.
You did not get it what i want to do.
I have a ma-20 .
I do have an obscure 80 columns adapter works only in an 60 Hz MSX.
never used them in one computer.

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