Cartridges using WAIT and CLK lines?

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Door WORP3

Paladin (863)

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06-01-2022, 10:44

With all of the clock modifications and slot expanders out there. Is it still save to use the CLK and/or open collector WAIT signal that are available on the cartridge slot?
Are there any known cartridges out there that already have used those signals and still work?

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Van ducasp

Hero (580)

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06-01-2022, 13:52

WAIT is really ok to use, and also consider using BUSDIR if your cartridge contains I/O devices that are accessed through IN/OUT, otherwise there is a risk that the data won't be read properly on expanded slots.

CLK is something that should be ok, as long as you don't expect it to be a certain value, as it is specified to be the CPU clock, so, it is not fixed in speed, and that is what makes quite a few cartridges fail or not work properly on machines that have turbo cpus / etc... If you need a fixed clock of a certain speed for your device, have your own clock generator, if you want to sync with the CPU clock, use the cartridge CLK signal.

That is my understanding.

Van sdsnatcher73

Prophet (3552)

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06-01-2022, 14:25

Ooh, what are you working on @WORP3… but yeah I agree with what ducasp said.

Van Grauw

Ascended (10623)

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06-01-2022, 15:31

I don’t think the cartridge CLK is specified to be the CPU clock. Just look at the Panasonic MSX2+ or turboR computers, it’s always 3.58 MHz.

The only situation where the cartridge slot CLK is not 3.58 MHz is for aftermarket 7 MHz upgrade mods. I guess preserving the 3.58 MHz clock on the cartridge slot is not practical for those, but as a result many modules that rely on CLK (like sound modules) fail to work properly, and the user will switch back to 3.58 MHz for any game or application that has music.

Oh, the 1chipMSX also incorrectly puts the CPU clock on the cartridge slot in turbo mode. Because of this my Yamaha SFG-05 only works in it at normal speed.

Van WORP3

Paladin (863)

afbeelding van WORP3

06-01-2022, 15:42

Thank for the input, so in general WAIT should be ok but it's better not to use the CLK as something that is synchronous to the CPU itself.

@Ducasp, always using the BUSDIR signal for cartridge outgoing signals.

@SdSnatcher73, Working on Paradoxs off-coarse Big smile

Van ducasp

Hero (580)

afbeelding van ducasp

06-01-2022, 17:28

Grauw wrote:

I don’t think the cartridge CLK is specified to be the CPU clock. Just look at the Panasonic MSX2+ or turboR computers, it’s always 3.58 MHz.

The only situation where the cartridge slot CLK is not 3.58 MHz is for aftermarket 7 MHz upgrade mods. I guess preserving the 3.58 MHz clock on the cartridge slot is not practical for those, but as a result many modules that rely on CLK (like sound modules) fail to work properly, and the user will switch back to 3.58 MHz for any game or application that has music.

Oh, the 1chipMSX also incorrectly puts the CPU clock on the cartridge slot in turbo mode. Because of this my Yamaha SFG-05 only works in it at normal speed.

The MSX Technical Data Book references the CLK on the slot as the CPU clock, also says the speed because at that moment it was fixed... So, I think that Panasonic took the easy way to keep compatibility with old cartridges that rely on the clock speed being 3.5x.... But since it is meant to be the CPU clock, if the CPU is driven by a faster clock, the correct approach would be to have the faster clock there... At least that is my interpretation, of course, that causes issues because since most (if not all) MSX machines had 3.5x CPU clock, interface designers might have took the assumption route that it would always be like that... Tongue

Van sdsnatcher73

Prophet (3552)

afbeelding van sdsnatcher73

06-01-2022, 19:11

Yeah it would be nice to know what the Victor HC-90/95 put on CLK in their Z180 turbo mode (CPU clock is a little over 6 MHz in that mode).

Van Danjovic

Champion (267)

afbeelding van Danjovic

06-01-2022, 20:41

WORP3 wrote:

With all of the clock modifications and slot expanders out there. Is it still save to use the CLK and/or open collector WAIT signal that are available on the cartridge slot?
Are there any known cartridges out there that already have used those signals and still work?

Do you intend to design/build a brand new peripheral that need both signals?

Van WORP3

Paladin (863)

afbeelding van WORP3

07-01-2022, 09:06

sdsnatcher73 wrote:

Yeah it would be nice to know what the Victor HC-90/95 put on CLK in their Z180 turbo mode (CPU clock is a little over 6 MHz in that mode).

That's one of the reason I was asking about this. In the meantime their are so much expansions that not always follow the original specifications that proper working of the clk is not always guaranteed. Handling the Wait signal depends largely on a good timing with respect to the CPU CLK. This all get's more complicated if you can't trust the CLK.

Van WORP3

Paladin (863)

afbeelding van WORP3

07-01-2022, 09:08

Danjovic wrote:
WORP3 wrote:

With all of the clock modifications and slot expanders out there. Is it still save to use the CLK and/or open collector WAIT signal that are available on the cartridge slot?
Are there any known cartridges out there that already have used those signals and still work?

Do you intend to design/build a brand new peripheral that need both signals?

Not necessarily want to use those signals, just looking at possibilities for a new challenge Wink

Van gdx

Enlighted (5714)

afbeelding van gdx

07-01-2022, 09:55

The standard specifies that the CLK on the slot is the CPU clock, and that the CPU clock is 3.58 MHz. So, the turbo modes are not standard except on the MSX Turbo R and on this computer the CLK on the slot is always 3.58 MHz. And this makes sense because a lot of hardware does not support changing frequencies.

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