USB to 9pinD serial adapters?
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From: Pd on 11 Feb 2010 20:35 Jaimie Vandenbergh <jaimie(a)sometimes.sessile.org> wrote: > Serendipitously, here's an interestingish diagram of ports over the > years: > http://www.appleinsider.com/articles/10/02/08/inside_apples_ipad_vga_video_out > put.html I love timeline stylee diagrams like that. -- Pd
From: Pd on 11 Feb 2010 20:36 Jaimie Vandenbergh <jaimie(a)sometimes.sessile.org> wrote: > The little holiday I just took was partly to get back into diving, and > I've never dived outside the UK before so it was spectacularly > impressive. And nice'n'warm. I was surprised how simple it is diving > wetsuit instead of drysuit... and 23'C rather than 4'C! The dive leader at Sodwana said she wouldn't get in the water if it was less than 26�C. Bloody Southern Hemisphere softies. Although I'm coming around to that way of thinking. -- Pd
From: David Empson on 11 Feb 2010 21:09 Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > Jaimie Vandenbergh <jaimie(a)sometimes.sessile.org> wrote: > > > I've just got back into scuba diving (thanks to a short holiday > > bobbing up and down in the red sea), and need to get my dive computer > > connected to slurp out my dives. It's a Suunto Vyper, and it's got an > > old 9 pin D shell serial connector. Nasty. > > > > I can buy a proper USB lead from the manufacturer, for a mere 65quids > > (which includes the software that I already have). Or I can buy a 3rd > > party USB cable for it which appears to be a builtin USB-serial > > converter, but that needs a driver - and they haven't got a Snow > > Leopard one yet. And it's 25 quid, anyway. > > http://www.customidea.com/shop/product_info.php?products_id=99 > > > > USB to serial adapters get a bad rep, rightly so, due to using 5V > > where serial should be 7-12V or some such. > > Wot? > > USB *IS* serial. But has almost nothing in common with simple serial interfaces like RS-232, apart from data travelling over two wires. USB is more than just a physical interface - it is an entire protocol suite (and not exactly a simple one). RS-232 is just an electrical and signalling standard. > You're talking about the ancient big iron and modem era RS232 standard, > superseded *in the 1970s* by backward compatible tech more suitable for > the world of modern microcomputer PCs in the 1970s but - alas - still with > us. EIA-232-D was introduced in 1986, superseding EIA-232-C (1969) and bringing it in line with V.24, V.28 and other standards. I have a book handy (from 1992) which covers that revision of the standard. RS-232 (or equivalent) has been the predominant standard in embedded systems for point to point short range connections until quite recently. It is still used for some devices that want to keep costs as low as possible, or for older products which are still being sold. RS-485 tends to get used for multi-drop and longer range applications. Some are using RS-422 or RS-423 instead of RS-232. (The Mac's serial ports were RS-422 and can be used as RS-423 by tying the RX+ line to ground and leaving TX+ unconnected.) In the last few years it has been possible to get off the shelf chips which implement a USB serial port on a chip, which can be added to an existing design to allow it to be connected to a computer via USB instead of RS-232 or similar. The device still uses asynchronous serial communication internally between the USB serial port and the CPU in the device (at logic levels, not needing RS-232 voltage conversion). Some microcontrollers have direct support for USB (as a peripheral), avoiding the need for a separate chip. They would typically be used in new designs. > The RS232 spec requires +/- 3V minimum tranmission voltage; spec says > -/+ 2.5V minimum reception thresholds, so 5V is marginally `you should > pick this up, but...' RS-232 transmitters must generate at least +/- 5V and receivers aren't required to handle anything less than +/- 3V. This means the Mac serial ports are not RS-232 compliant. They only transmit at about +/- 4.5V (which is fine for RS-422/423). > But: > > DC-DC converters to deal with this were standard fittings in the 1980s. The MAX232 (and similar chips) using a 4-capacitor charge pump are quite common from late 1980s in equipment we were making at work. It effectively gives you +/- 8V (or thereabouts, after loading) from a +5V rail. Earlier equipment used chips which required +/- 12V supply rail voltages for the transmitter (e.g. MC1488), but the receiver was able to operate off +5V (e.g. MC1489). > So there shouldn't be a problem - because this one should be dealt with > in a single chip that takes USB in at one end and chucks pukka > RS232-type signals out the other. I can't see any reason why not, not > these days. You can get a USB to RS-232 serial adapter, as per this thread. It is implemented by a chip in the adapter which acts as a USB peripheral, implements a UART (Universal Asynchronous Receiver/Transmitter), and is mapped to be a serial port on the host computer. Drivers usually need to be installed on the host. Additional circuitry is typically required in the adapter, such as a charge pump to get decent voltages. This is the same sort of chip I mentioned above which some devices used to "tack on" USB support to an existing product. > Rowland. > (who can't quite recall the /maximum/ RS232 voltage, but thinks it's > about 25V sending (+/- 12.5V) and 30V (+/- 15V) receiving. +/- 25V is the absolute maximum voltage for RS-232 (receiving). Transmitters are limited to +/- 15V. -- David Empson dempson(a)actrix.gen.nz
From: Rowland McDonnell on 11 Feb 2010 23:36 Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: [snip] > > RS422/423/etc uses balanced signalling like USB (and pretty much every > other sane serial comms link using wires). [snip] <thunk> And I checked before posting, /then/ realised my mistake. RS423 is the single-ended version of RS422, innit? Durr. Rowland. -- Remove the animal for email address: rowland.mcdonnell(a)dog.physics.org Sorry - the spam got to me http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking
From: Chris Ridd on 12 Feb 2010 01:46
On 2010-02-11 22:40:06 +0000, Elliott Roper said: > Snow Leopard want to add it as a modem, I just ignored that. GPSy X That's about the only problem with it - every time you connect it SL seems to want to add it as a new networking device. The latest 2.6b3 software may have fixed that... I'm pretty impressed that Keyspan have kept updating their drivers over the years, from PPC-only to PPC+Intel, and 64-bit Intel. -- Chris |