MSX Assembly Page

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By sd_snatcher

Prophet (3470)

sd_snatcher's picture

19-06-2015, 02:09

BTW, there's very little information about this DAC or the MIDI interface on the NMS-1205. Where can I find some programming docs about them?

Is this DAC at 0Ah 8bit signed or unsigned?

By Grauw

Ascended (10055)

Grauw's picture

19-06-2015, 18:23

Quote :

Where this information is sourced, from what official documentation, I do not know unfortunately.

By tvalenca

Paladin (747)

tvalenca's picture

19-06-2015, 18:31

What about this datasheet? http://www.analog.com/media/en/technical-documentation/data-...
It's an unsigned DAC, like the COVOX.

By Grauw

Ascended (10055)

Grauw's picture

19-06-2015, 18:45

Well the DAC itself is simple enough, just enable by outputting 1 on the Y8950’s IO0 pin and then write bytes to 0AH, as described by the first of the two (Dutch) links above. Going by the Dutch description, I think the data is unsigned so it’ll have a +0,256 DC offset, although that shouldn’t matter much and I wouldn’t rely on the accuracy of that tidbit.

It’d be nice if someone is aware of any official documentation from Philips which describes this, I could include it on the MAP. Always better to reference official docs rather than relying on community documentation.

By tvalenca

Paladin (747)

tvalenca's picture

19-06-2015, 19:00

sd_snatcher wrote:

Tip: The I/O ports overview page doesn't list the NMS-1205 2nd DAC (Covox-like) at (AFAIK) I/O port 0Ah.

Grauw wrote:

Quote :

Where this information is sourced, from what official documentation, I do not know unfortunately.

Well, I'm looking at Music Module's service manual right now and it seems quite bizarre to me. It is not decoding A0, A1, A2 and A4 while it is decoding A7, A6, A5 and A3 for DAC writes (A3 is not decoded by default on a MSX system). This way, any write from 08H to 0FH and from 18H to 1FH will write to DAC. There's also a repeated gate for IC6, so I think it's best to look inside the MM.

By sd_snatcher

Prophet (3470)

sd_snatcher's picture

19-06-2015, 21:47

@tvalenca

Are you sure? I've read the datasheet once and AFAICR this DAC could be configured for either signed or unsigned.

Have you checked how's it configured in the NMS-1205 service manual? I couldn't be sure since I'm no expert in analog circuitry, but I had the impression that it was configured for 8bit signed. Could you please explain why you reached the conclusion that it's configured as so?

By sd_snatcher

Prophet (3470)

sd_snatcher's picture

20-06-2015, 23:48

Confirmed: the DAC is indeed unsigned. Thanks, tvalenca!

By sd_snatcher

Prophet (3470)

sd_snatcher's picture

16-08-2015, 04:20

A small correction: The I/O ports overview page lists the bit-6 of the System control port as "Wait pin", but in fact it's related to the Light Pen. The subrom checks for the presence of an external Light Pen interface on I/O port BBh, and if there's one present it resets the bit6 of the F5h port.

By Grauw

Ascended (10055)

Grauw's picture

16-08-2015, 14:24

Thanks, corrected, katakana can be hard sometimes! Wink

Can you tell me which MSX systems those bits are set on, MSX2+, MSX2?

[Edit: removed silly question which I had already answered myself on the MAP Smile]

By Manuel

Ascended (18125)

Manuel's picture

16-08-2015, 17:26

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