Sharp C1 cannot use expansion audio?

[NewRisingSun]

As I am gathering Namco 163 cartridges for my expansion audio level measurement, I noticed that every single one of them mentions that it cannot be used with the Sharp C1. None of these games use the color deemphasis bits, to my knowledge, so I wondered what the reason would be. Then I looked at the Japanese Wikipedia page on the Sharp C1, which stated:

「ワギャンランド」などの後期に出されたナムコの作品や「燃えろ!!プロ野球」など、一部遊べないゲームが存在する。カセットが差し込まれているかの判定に、音声用の信号線を使用しているためである。拡張音声が使われているゲームでは、ソフトが差し込まれていないと判定され遊ぶことができない。イジェクトスイッチはない。前面からカセットを差し込む構造上、ディスクシステムやデータックは使用できない。

Machine translation:
There are some games that can not be played, such as Namco's work in the late stage such as "Wagan Land" and "Burning !! Professional Baseball". This is because a signal line for voice is used to judge whether a cassette is inserted. In a game where extended sound is used, it is determined that software is not plugged in and it can not play.

As I understand the machine translation, the Sharp C1 somehow uses the audio in and out pins to determine whether a cartridge is plugged in, and apparently the expansion audio interferes with this somehow. (The part about Wagyan Land must be a mistake however, as Wagyan Land does not have expansion audio.)

I had not read about this before at all.

[tepples]

Two guesses:

1. N163 games might be wired for sound mixing even if the game doesn't use it.
2. The deck also uses VRAM /CE out, like some of the OneBus famiclones do.

Do other games using cart nametable memory have this notice, such as Napoleon Senki and After Burner?

[nothingtosay]

I can't offer any insight myself, but this surprises me because Namco composer Hiroyuki Kawada said on Twitter that the company used C1s for Famicom development. Guess those who were working on expansion audio games must have used different hardware.

[NewRisingSun]

I do not have the manuals for all these carts, but the manual for megami tensei 2 has C1 screenshots, while the Youkai Douchuuki manual obviously has composite screenshots, both in color.

I also don't quite understand why the C1 would would need to specifically detect whether a cartridge is inserted or not. But I suppose Namco eventually figured out how to bridge that circuit in order to use it for development, or they just used a devboard without expansion audio.

[Great Hierophant]

I find it curious that the article mentions "Burning !! Professional Baseball", a.k.a. Moero!! Pro Yakyuu, which is a Jaleco game from 1987. That game bridges CIRAM /CE & PPU /A13 like most games do.

The NES CartDB does show that some Namco 163 games that use do not use the expansion audio bridge the audio pins (Dragon Ninja) and some do not (Dokuganryuu Masamune)

Would this issue cause any of these games not to work in a NES with a Fami-to-NES converter?

[lidnariq]

I assume the C1 automatically boots the cart and switches from TV mode to Famicom mode when a cartridge is inserted... or perhaps doesn't allow you to switch to the Famicom when there's no cart.

I don't see any reason to think the presence/absence of a short between those pins would cause a problem with anything other than the C1.