Why did Roland disable Request Data on the LAPC-I and the SCC-1?

Discussion about old sound cards, MIDI devices and sound related accessories.

Why did Roland disable Request Data on the LAPC-I and the SCC-1?

Postby NewRisingSun » 2017-11-02 @ 18:18

Assuming proper hardware set-up and correct setting of standard DOS environment variables, a well-written DOS game could completely eschew a SETUP program and rely entirely on auto-detection capabilities to select the optimal output device all by itself, except for one thing: when you detect a Roland MPU-401 interface, you don't know whether a General MIDI or an MT-32 compatible device is attached.

Telling between the two is possible if the device is an external module: Just send a Request Data (RQ1) sysex with an MT-32 Model-ID; if you receive something back, you have an MT-32, otherwise assume General MIDI. However, the most common MT-32 compatible device will be the Roland LAPC-I, and just like the SCC-1, the LAPC-I will never respond to an RQ1 sysex (see pages 17 and 21). This means that the most common MT-32 compatible sound source cannot be detected, only the MIDI interface can. Why, Roland? Other MIDI cards and daughterboards, including the original Wave Blaster, have no problem responding to request messages.
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Re: Why did Roland disable Request Data on the LAPC-I and the SCC-1?

Postby firage » 2017-11-02 @ 18:54

The MT-32 itself had to have always been a lot more common than the LAPC-I.

Guess it was easily overlooked in those days, when no other MIDI devices were supported on the interface. Then it seems it was too hard to enforce with GM. What if you had multiple devices, SCC-1 + MT-32 or LAPC-I + SC-55?
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Re: Why did Roland disable Request Data on the LAPC-I and the SCC-1?

Postby Cloudschatze » 2017-11-02 @ 19:39

RQ1 isn't technically disabled on the LAPC-I or SCC-1. Rather, there's no physical "MIDI OUT" connection between the synth and MPU-401 sections of either card. I imagine this decision probably has more to do with the lack of input merging/switching circuitry on the MPU-401 side than anything else.
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Re: Why did Roland disable Request Data on the LAPC-I and the SCC-1?

Postby Great Hierophant » 2017-12-09 @ 15:02

In terms of the most common MT-32 compatible device that is not an MT-32, I could see the LAPC-I as the answer. However, I think this only applies to US/Europe. In Japan, I would think the CM-32L would have been more popular because PCs were not as popular there.

If you want to rip MIDI from a game, the LAPC-I is not the easiest choice. Because the LAPC-I has no MIDI Out capability, you cannot receive a dump of the patch memory as you can with every other true MT-32 compatible on request. You would have to recover the patches from the stream of MIDI data going to the MCB-1, which means you need the MCB-1 as well.
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Re: Why did Roland disable Request Data on the LAPC-I and the SCC-1?

Postby keropi » 2017-12-09 @ 15:28

I think firage raises a valid point and most likely it's the reason for this behavior.
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