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The purpose of KILLGA aka JyDs is pretty well documented here insofar as the SMS is concerned, but I'm interested in whether any known carts (or indeed expansion peripherals) actually drive it.

In particular I'm interested in whether it's treated as wired-OR by convention or whether carts / peripherals assume they are the only ones driving it and therefore do so directly.

Any insights appreciated!

Probably not what you are asking, and you already know it (as you are specifying SMS), but it is used by the keyboard (SK-1100) when connecting to the SG1000 or Mark III.

kamillebidan wrote

Probably not what you are asking, and you already know it (as you are specifying SMS), but it is used by the keyboard (SK-1100) when connecting to the SG1000 or Mark III.

Thanks @kamillebidan, that's very interesting.
I had a look at some schematics Wasup posted some years ago but couldn't immediately see where KILLGA comes in. Still, it's late and I'm tired — will look again tomorrow!

I'm only aware of peripherals like FM Sound and Keyboard that have IO ports mapped in the $C0-$FF region using it. But someone may know for sure if any cartridges or cards did in fact use it and chime in.

Good practice would be to have a 330 or 1K series resistor in any device that drives the line. I didn't put one in the circuit for Lionheart but I have a note about it at the bottom of the diagram.

asynchronous wrote

I'm only aware of peripherals like FM Sound and Keyboard that have IO ports mapped in the $C0-$FF region using it. But someone may know for sure if any cartridges or cards did in fact use it and chime in.

Thanks @asynchronous!

I had thought FM sound uses it, but from what little I could scrap together on it (are there schematics anywhere of systems that have it built in??) I wondered if it relied on the software switch in port $3e rather than the than KILLGA; indeed even whether it needed to disable the GA at all since does the FM control only require writes in that range?

asynchronous wrote

Good practice would be to have a 330 or 1K series resistor in any device that drives the line. I didn't put one in the circuit for Lionheart but I have a note about it at the bottom of the diagram.

Agreed, that was my fallback position but was idly trying to dream up something that felt more "orchestrated". It's mildly annoying that the logic to disable the GA is active high, as it would fit my plans nicer as active low and I could use one of my spare open drain buffers to drive it. Oh well!

FM sound unit provides one read/write port to both enable and is used for automatic detection. KILLGA has to be used to prevent a bus conflict when reading from that.

Later consoles (GG, Megadrive in Mark3 mode) neither provide nor need KILLGA because they don't drive the data bus during reads from I/O address $F2.

Enri's notes seem to imply that the Japanese SMS fully decodes the I/O ports (like the GG and Megadrive) instead of having 32 mirrors that need to be disabled.

lidnariq wrote

FM sound unit provides one read/write port to both enable and is used for automatic detection. KILLGA has to be used to prevent a bus conflict when reading from that.

Later consoles (GG, Megadrive in Mark3 mode) neither provide nor need KILLGA because they don't drive the data bus during reads from I/O address $F2.

Enri's notes seem to imply that the Japanese SMS fully decodes the I/O ports (like the GG and Megadrive) instead of having 32 mirrors that need to be disabled.

Thanks @lidnariq! Based on these clues I've managed to do a little more digging although I have to say that it's tough finding all the documentation for FM sound in one place here, perhaps it might be worth me putting together a collating wiki article at some point.

I actually didn't realise that the GG decoded the full I/O address although it would make sense since the ASIC takes all the address lines anyway. What is much more surprising is that the JP SMS does also, but I agree that does appear to be implied.
(EDIT: and the schematic referenced below also confirms that all 16 address lines appear to be available to be decoded)

I'm still a little confused though, since you mention that KILLGA has to be used to avoid contention, but surely it's just as easier to use port $3e and software for that, since port $f2 is used by software for FM detection.

In fact, port $3e is used in this FM chip detection routine to presumably avoid the contention.

Also, perhaps not completely reliable (and my eyesight might be failing me), but if I look at the schematics for the JP SMS posted here, I can't see KILLGA being driven by anything. I can see it going into the GA, and I can see it on the expansion port but I can't see the FM unit driving it or indeed anywhere else, including the cartridge port.

Author	Message
willbritton Joined: 06 Mar 2022 Posts: 671 Location: London, UK	Anyone know of any carts that use KILLGA / JyDs? Posted: Sun Sep 03, 2023 2:11 pm
	The purpose of KILLGA aka JyDs is pretty well documented here insofar as the SMS is concerned, but I'm interested in whether any known carts (or indeed expansion peripherals) actually drive it. In particular I'm interested in whether it's treated as wired-OR by convention or whether carts / peripherals assume they are the only ones driving it and therefore do so directly. Any insights appreciated!

kamillebidan Joined: 25 Feb 2013 Posts: 384 Location: Osaka	Posted: Sun Sep 03, 2023 11:33 pm
	Probably not what you are asking, and you already know it (as you are specifying SMS), but it is used by the keyboard (SK-1100) when connecting to the SG1000 or Mark III.

willbritton Joined: 06 Mar 2022 Posts: 671 Location: London, UK	Posted: Sun Sep 03, 2023 11:59 pm
	kamillebidan wrote Probably not what you are asking, and you already know it (as you are specifying SMS), but it is used by the keyboard (SK-1100) when connecting to the SG1000 or Mark III. Thanks @kamillebidan, that's very interesting. I had a look at some schematics Wasup posted some years ago but couldn't immediately see where KILLGA comes in. Still, it's late and I'm tired — will look again tomorrow!

asynchronous Joined: 14 Aug 2000 Posts: 742 Location: Adelaide, Australia	Anyone know of any carts that use KILLGA / JyDs? Posted: Mon Sep 04, 2023 2:52 am
	I'm only aware of peripherals like FM Sound and Keyboard that have IO ports mapped in the $C0-$FF region using it. But someone may know for sure if any cartridges or cards did in fact use it and chime in. Good practice would be to have a 330 or 1K series resistor in any device that drives the line. I didn't put one in the circuit for Lionheart but I have a note about it at the bottom of the diagram.

willbritton Joined: 06 Mar 2022 Posts: 671 Location: London, UK	Posted: Mon Sep 04, 2023 7:00 am Last edited by willbritton on Mon Sep 04, 2023 7:36 pm; edited 1 time in total
	asynchronous wrote I'm only aware of peripherals like FM Sound and Keyboard that have IO ports mapped in the $C0-$FF region using it. But someone may know for sure if any cartridges or cards did in fact use it and chime in. Thanks @asynchronous! I had thought FM sound uses it, but from what little I could scrap together on it (are there schematics anywhere of systems that have it built in??) I wondered if it relied on the software switch in port $3e rather than the than KILLGA; indeed even whether it needed to disable the GA at all since does the FM control only require writes in that range? asynchronous wrote Good practice would be to have a 330 or 1K series resistor in any device that drives the line. I didn't put one in the circuit for Lionheart but I have a note about it at the bottom of the diagram. Agreed, that was my fallback position but was idly trying to dream up something that felt more "orchestrated". It's mildly annoying that the logic to disable the GA is active high, as it would fit my plans nicer as active low and I could use one of my spare open drain buffers to drive it. Oh well!

lidnariq Joined: 24 Mar 2021 Posts: 120	Posted: Mon Sep 04, 2023 7:00 pm
lidnariq Joined: 24 Mar 2021 Posts: 120	FM sound unit provides one read/write port to both enable and is used for automatic detection. KILLGA has to be used to prevent a bus conflict when reading from that. Later consoles (GG, Megadrive in Mark3 mode) neither provide nor need KILLGA because they don't drive the data bus during reads from I/O address $F2. Enri's notes seem to imply that the Japanese SMS fully decodes the I/O ports (like the GG and Megadrive) instead of having 32 mirrors that need to be disabled.

willbritton Joined: 06 Mar 2022 Posts: 671 Location: London, UK	Posted: Mon Sep 04, 2023 7:47 pm
	lidnariq wrote FM sound unit provides one read/write port to both enable and is used for automatic detection. KILLGA has to be used to prevent a bus conflict when reading from that. Later consoles (GG, Megadrive in Mark3 mode) neither provide nor need KILLGA because they don't drive the data bus during reads from I/O address $F2. Enri's notes seem to imply that the Japanese SMS fully decodes the I/O ports (like the GG and Megadrive) instead of having 32 mirrors that need to be disabled. Thanks @lidnariq! Based on these clues I've managed to do a little more digging although I have to say that it's tough finding all the documentation for FM sound in one place here, perhaps it might be worth me putting together a collating wiki article at some point. I actually didn't realise that the GG decoded the full I/O address although it would make sense since the ASIC takes all the address lines anyway. What is much more surprising is that the JP SMS does also, but I agree that does appear to be implied. (EDIT: and the schematic referenced below also confirms that all 16 address lines appear to be available to be decoded) I'm still a little confused though, since you mention that KILLGA has to be used to avoid contention, but surely it's just as easier to use port $3e and software for that, since port $f2 is used by software for FM detection. In fact, port $3e is used in this FM chip detection routine to presumably avoid the contention. Also, perhaps not completely reliable (and my eyesight might be failing me), but if I look at the schematics for the JP SMS posted here, I can't see KILLGA being driven by anything. I can see it going into the GA, and I can see it on the expansion port but I can't see the FM unit driving it or indeed anywhere else, including the cartridge port.

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