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Thread ID: 43911	2004-03-31 10:58:00	USB to Serial Convertors	Billy T (70)	Press F1

Post ID	Timestamp	Content	User
226233	2004-03-31 21:07:00	I've been using a DSE one of these for 9 months with no problems, but now you guys have got me worried!	falvrez (390)
226234	2004-03-31 21:35:00	I've been using a DSE one for about 12 months. No problems. One thing. They seem only to work with Windows apps. Anything designed around DOS com port asignments seems to have problems.	paulw (1826)
226235	2004-03-31 23:04:00	Ahhh......... You might have nailed one of the issues there Paul. :( Some of my instruments have Windows software and some have DOS, however while this doesn't alter the fact that my current DSE convertor is deader than Monty Python's parrot, it does explain some of my difficulties. As a matter of interest, I have a D-Link DU-H3SP USB hub on my PIII box and that has serial and parallel ports on the back. The parallel port works OK, but I hadn't tried the serial before so I gave it a run this morning and found that it would download data from a Windows instrument OK but wouldn't accept data from a DOS program. It would create the correct file name and write the header info, but that comes from the program itself. It was the data transfer that failed, and I don't understand this because to my simple mind it is either a serial port or it isn't. To my way of thinking the instrument should see a standard serial port (emulating Com 3 in this instance) and how the USB end delivers the data to the correct file address shouldn't matter. Maybe they haven't been formally introduced and the proper handshaking isn't taking place. Any ideas on why the communication might be failing on an otherwise working convertor? Cheers Billy 8-{)	Billy T (70)
226236	2004-03-31 23:15:00	Its a "virtual" serial port. DOS usually requires a "real" serial port. DOS does not understand USB, and this is where the virtual port is mapped from as I understand it. I have had no success with DOS applications using converters and made sure when I purchased a laptop that it had a "real" RS232 port.	godfather (25)
226237	2004-04-01 00:45:00	Do you think that This (www.amazon.com) might be a viable solution? Specs are a little below the image. I'll download & read the manual. Cheers Billy 8-{)	Billy T (70)
226238	2004-04-01 00:48:00	Bugger! Manual was for the MAC version only. Cheers Billy 8-{(	Billy T (70)
226239	2004-04-01 00:54:00	> Its a "virtual" serial port. > DOS usually requires a "real" serial port. > > DOS does not understand USB, and this is where the > virtual port is mapped from as I understand it. > > I have had no success with DOS applications using > converters and made sure when I purchased a laptop > that it had a "real" RS232 port. I second godfather on that one. Having written a number of DOS based applications that use the serial port to communicate with embedded devices I was forced to try these USB adapters and found that they all failed... Odly enough even attempting to use many of them in windows as a standard serial port, using standard serial APIs, produced some strange results so after some research I found it was necessary to open the "virtual" port a bit differently from a "real" serial port. One thing was very clear from my research, the USB devices REQUIRE handshaking to work properly.	ugh1 (4204)
226240	2004-04-01 02:42:00	I learnt very early to write code to access the serial port registers direct, rather than through the DOS COMx: devices. It might not be "device independent" programming, but it works. :D Even using Windows programmes, which can talk through a USB adapter, it might pay to ensure that the plugs from slave equipment supply the jumpering which the "DOS standard" wants on the status lines, rather than just the Rx, Tx, gnd which you can get away with if you use bare-metal programming.	Graham L (2)
226241	2004-04-01 02:45:00	> One thing was very clear from my research, the USB > devices REQUIRE handshaking to work properly . So how do we ensure that handshaking takes place? I have now completed some fairly intensive research and it appears that some users have achieved reliable DOS connectivity with legacy devices using a dos emulation box under the USB com port properties . There is a distinct lack of "how to" involved and it appears that some application-specific software may have been written in one case to set up the interface . The problem is recognised and solutions appear to exist, but I haven't located anything solid enough to invest any more time on yet . It also appears that there are only five or so manufacturers of USB to Serial convertors and just about everything I found looked like a house branded example of one of those 5 except for DSE and Radio Shack . What I have discovered is that there are a number of non RS232 compliant serial ports around, some predating USB, with voltage swings as low as +/- 5 volts instead of +/- 12 volts (or so they say) . Only one brand of USB to serial adapter claims full compliance with the RS232 spec so that looks like a promising product to buy . One of my instruments is very picky indeed about interface conditions, so much so that it will not work at all on my Libretto 50CT on batteries but works every time on mains power . I had a similar problem on my old 486 which had two cards and four ports . It would only work reliably on one card and there was a 75% failure rate on the other . By chance the compliant model is available from a local retailer :D so I can try it and see, and return it if it doesn't work . I guess I could even try it in-store if they'll let me . Cheers Billy 8-{)	Billy T (70)
226242	2004-04-01 02:50:00	> I learnt very early to write code to access the > serial port registers direct, rather than through the > DOS COMx: devices . Can you provide some pointers on that Graham? > It might pay to ensure that the plugs from slave > equipment supply the jumpering which the > "DOS standard" wants on the status lines, > rather than just the Rx, Tx, & gnd And expand a little on this point too please . No hurry :D Cheers Billy 8-{)	Billy T (70)
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