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POKEY, two-tone mode, 1030 tone dialing, and the 400


hunmanik

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In the 1030 Modem Owner's Guide Atari states (page 7; pdf page 9):

 

If you have an Atari 400 Home Computer, you cannot use the tone (push-button) dialing feature to dial from your computer's keyboard.

 

What is unique about the 400 to result in this limitation?

 

Since I understand that POKEY generates the tones for tone dialing for the 1030, does this reflect something unique about the way POKEY is connected in the 400?

 

 

Related question is, does POKEY generate the dial tones for the 1030 in a similar way to its generation of the Mark and Space tones for recording to cassette? That is, using two-tone mode to produce sound over SIO serial data out pin 5?

 

I barely grasp how two-tone mode for cassette recording works as it is, and now I'm further trying to understand how two-tone mode would be applied to generating a full set of dial tones.

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400 and 800 should have identical serial capabilities, and the Pokey chip itself is the same throughout the entire range.

 

The thing with 2 tone mode is that only one tone is ever played at a time. Phone DTMF systems generally use 2 simultaneous notes to represent numbers and symbols. Although Pokey can do this just fine, the serial output only supports either 0/5V logic or the 2-tone mode with the restriction I mentioned before.

 

Additionally, the keyboard on 400 though membrane vs full stroke otherwise functions identically to the 800.

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How big is the modem software? I'm thinking perhaps it loads in modules and detects your amount of memory so if your Atari 400 was an early model with just 8K RAM, the part of software that does tone dialing might be excluded? I understand later 400's as well as the 600XL of course came with 16K RAM which may be the lower end for all functions to be included.

 

The fact that you must not use a tape recorder, and any floppy drive you have installed must remain powered off, would greatly limit the use of the 1030 modem for downloading software unless you can power on the floppy drive to store what is downloaded to memory, power it off to download more data etc.

 

Edit: Aha, the ModemLink software is in ROM so the amount of RAM might not be a factor, in particular since the software doesn't have any means of file transfer.

 

I did find an Antic article though, that doesn't single out the 400 for lacking tone dialing capacity.

http://www.atarimagazines.com/v4n4/1030modem.html

Edited by carlsson
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According to Jerzy Sobola's schematic, SIO Pin 11 (Audio In) is piped into the EXI (external audio input, pin 17) pin of the modem chip. Well, that's odd since it's supposed to an audio input into the computer.

 

http://www.syntax.com.tw/upload/pdf/IC-TMS99532.pdf

http://www.dereatari.republika.pl/atarisch/1030.zip

 

Are they relying on Pokey leakage out of this pin for tone dialing? It would make more sense to do it with the 8048 controller in the modem.

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In ANTIC interview #10 with Mark Rustad, he explains they did exactly that - amplifying pokey leakage. The R: routine has tables of digitized 4-Bit DTMF sine waves which would the POKEY would play back, and the 1030 would amplify off the AUDIO IN line, to get a wave 'close enough' to pass Bell certification. He also mentioned there was something about a slightly different table needed for the 1200XL due the non-linear amplitudes associated with the POKEY.

 

A total hack haha. After all that effort for Bell certification for USA, no wonder they never released modems in other countries outside north america - where they'd have to repeat the certification process all over again.

 

Maybe the POKEY leakage hack just didn't work on 400's?

 

http://ataripodcast.libsyn.com/antic-interview-10-the-atari-8-bit-podcast-mark-rustad

Edited by Nezgar
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Re-listened to the Rustad interview just now, thanks!

 

And, outstanding! I guess I didn't appreciate the hack involved when I heard him explain it the first time.

 

So, the tones for 1030 tone dialing are generated by POKEY using its 4-bit PCM Volume Only mode, and the 1030 manages to pick up the sound as noise over the SIO audio INPUT line, SIO pin 11.

 

It sounds like they almost had to come up with unique routines for each computer model, or at least the 1200XL needed a different implementation for its unique sound circuit characteristics.

 

As to why not on the 400... Not enough audio output signal leakage onto the SIO audio input line on the 400 would seem the most likely explanation.

 

Does 1030 tone dialing work on XE computers? It seems like it would almost be a fluke if it does. It would depend on how similar XE sound circuitry is to that in the earlier machines.

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Personally I've never had a 1030 (I started with an Avatex 1200bps and a P:R: connection) I would think the XM301 is pretty much the exact same deal as the 1030, and I did borrow one from a friend back in the day just to try on my 130XE, and it sure seems like that trick was in use, hearing the DTMF tones and phone line sounds coming out of the TV speaker.

 

So based on that I would presume the 1030 would work just fine on a 130XE or other newer machines.

 

Funny that the software DTMF was basically a hardware cost savings measure... and the 'apparently better' audio separation on the 400 burned them haha.

Edited by Nezgar
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  • 3 years later...
On 8/2/2017 at 12:40 PM, Nezgar said:

A total hack haha. After all that effort for Bell certification for USA, no wonder they never released modems in other countries outside north america - where they'd have to repeat the certification process all over again.

Total thread necro, but I can remember seeing SX212s for sale at the main Atari retailer in Dublin, Peats.  Other countries may have also received them; I want to say that I have vague recollections of them being advertised by UK retailers for use with the ST range (though they probably needed an RJ11 to whatever-it-was-BT-used-on-their-flat-plug adapter or cable).

 

A lot of countries really didn't care about local certification as long as they collected import duties on them when they came in.  Enforcement would be more of a pain than it was worth, though that didn't prevent it happening in some.

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@x=usr(1536) I think my comments mostly pertained to not releasing the "older" modems like 830, 835, 1030 outside of North America... The 835, 1030 and XM301 at least seemed to be internal Atari designs, whereas the SX212 was more of a re-branded hayes compatible chipset. I believe the 830, which was really just a rebranded "CAT" modem was only available for a short time in the 80-81 era before the 835 model was available/approved...

 

As far as distribution, the XM301 & SX212 came out later in the Tramiel era, so it would make sense to have been more widely distributed outside of North America...

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9 hours ago, Nezgar said:

@x=usr(1536) I think my comments mostly pertained to not releasing the "older" modems like 830, 835, 1030 outside of North America...

Yep, understood.  And my experience may (read: probably doesn't) match what others may have seen in their countries.  Certainly, I can't remember seeing an Atari-branded modem prior to the SX212 in Ireland, but I'm sure a few made it in from people who bought them on holiday in the US.

 

As an aside, we technically weren't supposed to have self-purchased modems until about 1988 or so - they were meant to have been rented from Telecom Eireann.  Nobody apart from larger businesses really bothered with that and I can't think of anyone who was ever prosecuted for using an unapproved modem.

9 hours ago, Nezgar said:

The 835, 1030 and XM301 at least seemed to be internal Atari designs, whereas the SX212 was more of a re-branded hayes compatible chipset. I believe the 830, which was really just a rebranded "CAT" modem was only available for a short time in the 80-81 era before the 835 model was available/approved...

The SX212 was definitely a rebrand, though I can't remember of whose modem.  Ditto the 830, which I believe you're correct was a CAT.  From what I recall, it was basically the same as the AppleCAT modem.

9 hours ago, Nezgar said:

As far as distribution, the XM301 & SX212 came out later in the Tramiel era, so it would make sense to have been more widely distributed outside of North America...

True.

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