Chuck Guzis wrote: Same place as the 9V DC wall warts ... I could not find one for love or money. Had to pick a universial adapter, instead today.

On Thu, May 28, 2009 at 17:57, Ethan Dicks <ethan.dicks at gmail.com> wrote: I thought it was too fuzzy to see, but I guess he typed http://en.wikipedia.org - this makes sense since otherwise he'd have gotten the language selection screen. Joe. -- Joachim Thiemann :: http://www.tsp.ece.mcgill.ca/~jthiem

David Griffith wrote: I have one of the same model as shown in the video (Livermore Data Systems model A). Component date codes in mine are 1969/70, the 1964 suggestion may be a little early, but I guess it depends on how long they were producing them for. Very elaborate woodwork for the task (solid teak or walnut with dovetail joints) but I suppose the wood case had some acoustic advantages. 13 transistors. (pedantic: His technical description was a little off, it's FSK, not an 'interrupted' tone.) Does anyone know if the frequencies for the 110 and 300 baud modem standards were the same or different?

On Fri, 2009-05-29 at 07:34 -0500, Chris Elmquist wrote: So, you can't see a possible set of circumstances where having the wrong voltage coming in the serial port could cause the frequency shift to be wrong? How clever do you think the tone generator side is? Gordon

Gordon JC Pearce wrote: It's not inconceivable and the circuit is not overly clever, but it is good enough to have a trip point over a 0.03 volt range, between +1.26 to +1.29 volts. The tones are pretty solid +/- 4 Hz between there and +/- 25 volts; +/-1 Hz for +/- 3 to 25 volts, so all well within RS-232 requirements. (As measured on my unit, I suppose the utube guy's unit could have a problem.) Here's the schematic for amusement (note measurements), pretty simple except for the specced coils: http://www3.telus.net/~bhilpert/tmp/LDSModelAModem.gif The reason the tone changes when he plugs in the RS-232 connector in the video is the open-circuit state for the modem modulator is SPACE, while idle-state for RS-232 is MARK.

On Saturday (05/30/2009 at 10:37AM +0100), Gordon JC Pearce wrote: Well, as Tony replied-- I think that the RS232 input is a logic level. It's not an analog level. So, you are going to get either the mark tone or the space tone and not something in between. I think this situation was just a poor explaination of what went wrong. Whatever miscable situation he had caused him to generate the opposite tone of what he was expecting but not a tone that was off frequency from one of the two possibilities. He was also off the mark (so to speak) by attempting to explain it as on-off keying rather than the FSK that it really is. Chris -- Chris Elmquist

Dave McGuire wrote: It's a very primitive originate-only modem, I beleive my previous post explained the mark-space tone behaviour the fellow was observing when he plugged the cable in. I don't see any unexpected behaviour from (my instance of) the modem. One would have to go through hoops to get mark/space reversed. If there was some other problem I think it must have been a configuration issue on the DTE/terminal-emulation end. As Chris says, his explanation was a little off.

On Mon, 2009-06-01 at 15:32 -0400, Mark G. Thomas wrote: Okay, let's try again. I have a circa-70s 300-baud modem, that will generate incorrect tones when it's plugged into a USB-to-serial converter, but not when it's plugged into a real serial port. Why might this happen? Gordon

Waht's the make and model of the modem? Have you measured the voltage on the RS232 TxD pin in both cases? -tony

Gordon JC Pearce wrote: I've had problems with USB serial devices feeding various things, but mostly things that draw too much current. Most USB devices seem to only have +/-5v swings and if you draw too much current the sag quickly. Older PC's seem to have much better +/-12v swings and can supply more current. I have some digital thermostats which draw from DTR and will only work with a pc - they won't work with the +/-5v of a USB device because the voltage sags too much. With these same "problem" devices I've also not had much luck with simple max232 style outputs; they give a nice +/-10v swing but also sag quickly. I think the drivers have wimpy NP caps (like .1uf). I could try beefing those up and seeing if that helps. -brad

On Thu, Jun 4, 2009 at 1:56 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote: One wonders if the in-house product test was more rigorous than connecting two devices with a 2m cable and sending a few characters at 9600 bps, or more likely, the engineers said that the design as given wouldn't meet the formal spec without spending $0.25 on more robust components and were told to keep it cheap since it would probably work for most customers, or at least work well enough that few customers would return the item. The USB serial devices I've seen have been a 1-chip design - presumably USB, UART, and level converters all on one die, with a few discretes for the DC-DC converter. I don't remember seeing any separate Maxim devices in them. We had something like that happen with our Qbus COMBOARDs when an early customer installed theirs into a Qbus backplane that didn't provide -15V (which is, ISTR, most of them). Things didn't make sense until we figured out the lack of negative voltage to the 1488s/1489s. Every Qboard after that had a DC-DC converter on it (and I still have dozens of those, new on the slab of foam). -ethan

On Fri, Jun 5, 2009 at 11:21 AM, Jochen Kunz <jkunz at unixag-kl.fh-kl.de> wrote: I think our issue (and maybe DEC's as well), is that old (16 bit?) Qbus backplanes provided -15V, but not the BA23 and newer. I might be mistaken, but we did start Qbus product development before we had a MicroVAX-I on site. We tested with a 4-slot LSI-11 box (and the Fluke 9010A I was talking about last week) for initial functional testing (CSR bits, DMA, local RAM/ROM, etc.) I do remember that the Rev 0 board had a DC-DC converter attached in dead-bug mode. -ethan

On Fri, Jun 5, 2009 at 3:46 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote: Or tell you just to reinstall the drivers. :-P I know there are "FTDI"-based USB seriual converters which would presumably also have either an external MAXnnn or a bunch of discretes for a charge-pump and level conversion, but I haven't dismantled any of those. The ones I have dismantled (by sliding the plastic housing away from the DE-9) were because they were ultra-cheap (like $4 at the Thrift Store) to see what it would take to route +5V from the USB cable over pin 9, since I have a few serial-interfaced devices, like a toolbooth terminal, that the only external connection is a DE-9 w/pins 2, 3, 5, and 9 passing in/out (TxD, RxD and GND on the expected pins, plus Vcc on pin 9). The hack would be simple - sever any connection between the DE-9 pin 9 and the PCB, then run a jumper wire across the inside of the adapter and reassemble (or in one case, mount inside the enclosure and run the USB cable out a new hole). I realize it's no standard, but I've seen power-over-pin-9 enough to want a simple hack instead of these reverse-Y-cables I've made to tap serial and either PS/2 or USB for power to run these items. The extra cable gets a little clunky after a while. -ethan

Small tip here: The FT-232 chip is a hell of expensive. Buy an old NOKIA data cable (one with the fun port connector) or like (siemens, maxom, any very old data cable) for $1 and you have the USB-to-TTL-Serial(needs max-232 to be a full usb to rs-232 cable) for a cheap. I do it everyday here. Greetz from Brazil, PU1BZZ Alexandre

(fast answer, I'm doing barbecue here, anyone served? :D) Since this info may interest other people, I'll do a small page with photos, drivers, etc and put it online, hope to do it this night, hold on. Usually they use the prolific chipset, I'll send more detailed info later today Gfb Alexandre, PU1BZZ

Gordon JC Pearce wrote: If you put enough voltage through a serial port signal, you'll break the modem. Then you'll probably get a fixed frequency regardless of the input, or no frequency at all. Other than that, no, having the wrong voltage won't cause the frequency shift to be wrong. Clever enough that its frequency isn't a linear function of the serial port signal voltages. Modems with EIA-232 (formerly RS-232) interfaces detect whether the transmit data signal has a voltage above or below a threshold, and generate one of two tones based on that. They don't feed the transmit data signal directly into a VCO, if that's what you were thinking. Doing it that way wouldn't result in a reliable modem, since an EIA-232 mark signal can be anywhere from -3V to -25V, and a space For current loop, it senses current rather than voltage, but the principle is the same. It doesn't base the tone on the precise amount of current flowing, because even in a loop that has a nominal current (i.e., 20mA), the actually current may be significantly different.

On May 28, 2009, at 7:04 PM, Eric Smith wrote: An eBay seller has a number of TMS99532s available at $2.75/ea, item # 110376664450. -Dave -- Dave McGuire Port Charlotte, FL

On May 28, 2009, at 9:00 PM, Chuck Guzis wrote: I honestly don't recall, but I seem to recall their having been more components than a TMS99532-based design would require. -Dave -- Dave McGuire Port Charlotte, FL

On May 28, 2009, at 9:26 PM, William Donzelli wrote: Wasn't that a baud rate generator? Or is that the 14411? -Dave -- Dave McGuire Port Charlotte, FL

No, the 14412 is a modem IC, and the 14411 is a buad rate generator. I've used both not that long ago... -tony

Fred wrote: Chuck wrote: Many ASR33s were equipped with an acoustic coupler to the right of the keyboard and printer, and they didn't have any cover to exclude outside noise. They worked fine even though the ASR33 itself was quite noisy, because 103 FSK modulation at 110 baud [*] had a lot of noise margin. Eric [*] These were actually 110 baud, since there was a one-to-one mapping of bits to modulation symbols. Later modems were often incorrectly described as 1200 baud, 2400 baud, 9600 baud, etc., when in fact the quoted number was their data transfer rate in bits per second, and the baud rate was a fraction of that.

On Thu, May 28, 2009 at 8:16 PM, Eric Smith <eric at brouhaha.com> wrote: I thought that started at 2400 bps (600 baud, 4 bits-per-baud)? -ethan