The best USB-serial Interfaces for Linux are the ones with FTDI Chip inside. http://www.ftdichip.com/
http://www.ftdichip.com/Products/EvaluationKits/USB-Serial.htm Rainer

The best USB-serial Interfaces for Linux are the ones with FTDI Chip inside. http://www.ftdichip.com/ http://www.ftdichip.com/Products/EvaluationKits/USB-Serial.htm

Do they have the same latency as a normal serial port? I've tried several usb-serial ports, and they all have horrible latencies compared to an onboard (or PCI card).

We tried USB converters with prolific chipset and it hangs up then, so FTDI chips would be better. I read also somewhere a lack of latency. May be it is also a question of the Kerneldriver and the driver will improve more in the future.

I have two Prolific 2303 serial converters without problems. There is native USB support in the kernel (2.6.17). I have run am interested in your problems - maybe I can prevent some future problem.

John

Does anyone know about USB-to-Serial for DOS? I would be very interrested (Even Ethernet-to-Serial).

Andreas

We mostly use a serial (either using a RS422 converter or straight) to contact a PIC for the realtime part of our applications. The latency is also there under Windows, and messes up the realtime aspect of signaling. (actually, while I used the converters under Linux, I haven't latency benchmarked them yet)

For me the latency is not (very) important. I do not feel a lack of latency. We tried USB converters with prolific chipset and it hangs up then, so FTDI chips would be better. I read also somewhere a lack of latency. May be it is also a question of the Kerneldriver and the driver will improve more in the future.

Rainer

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It's more likely a general problem of USB.
A real serial port is always ready to receive and it triggers an

interrupt as soon as it has received a character, so the PC immediately fetches the received data.

On USB the converter must buffer all incoming data until the PC specifically asks it to do its next transfer. On USB1 there is no guarantee that the PC can do
1000 transfers per second.
USB1 can transfer a lot more than 1000 bytes per second, but not in 1000 transfers of only 1 byte each.
I don't know the exact number for USB2.
Also it depends on which other USB devides are connected because they all share the bus.

Klaus

I've come across a website discussing connection of a USB CD-ROM drive to a DOS system for booting purposes but I've not seen reference to serial devices. I think the people to ask about this might be Parallax since they use USB-connected serial ports for device programming, if anybody knows how to hook them onto older machines they will.

My own feeling if you /have/ to have a DOS environment and don't mean something like the '98 DOS box would be to see if you could run the code under either DosEmu or Qemu, both of which allow guest session ports to be mapped to whatever hardware is supported by the host. I've got one system here where DosEmu has been set up to allow software direct access to an lpt port so it can control an EPROM blaster, but obviously that sort of thing wouldn't work where the physical device types differed.

Thanks for the tip.

Actually, I use DOS directly. I use cheap off-the-shelf motherboard for an embedded system that our company uses. The motherboard talks the the system (which may be spread over kilometers) via a single serial port at 9600 baud. My problem is that there are cheap motherboards appearing that no longer have serial ports. I'm afraid that soon none will. Therefore I am looking for alternatives.

Andreas

We also had this problem, but in the end decided to stuff PCI serial cards into it. (typically they cost Eur 18 or so).

One of the main reasons were the high latency of the usb-serial (or straight USB to the PIC). The other option (go networked) is still on hold, since that requires way more work PIC side. (we use 8-bitters still)

You might find it easier to design a serial expansion module, alternatively migrate to something that supports the PC/104 interface which is likely to have serial modules available for the forseeable future. If it's for embedded work the last thing you want to do is add GOK how many thousands of gates and lines of driver code to replace a simple piece of hardware; having said that I'm in much the same position and have considered USB as well since it's significantly cheaper than an 8-port card.

Andreas Berger wrote

My problem is that there are cheap motherboards appearing that no longer have serial ports. I'm afraid that soon none will. Therefore I am looking for alternatives.

I'm running also a DOS Program and now it is ported to Linux.

Actually it runs on both platforms!

Graphical output is done with framebuffer mode and in Linux you can switch to runlevel 2 (text mode only) and if you had set the correct graphical mode in the bootloader you can switch into direct framebuffer mode from the console. Using a Knoppix live Linux CD installed at the harddisk switching off the KDE stuff.
It is not that hard that it may seems to port a DOS program to Linux I would say now in a rewiev.
In Linux you have the advantage that you don't have to search for drivers and so on...
I would like to add ISDN capability to the program. I don't now if it is that easy in DOS... The same with Internet connectivity... Also the Harddrive capabilities are not limited... Also you can make a diskless-system easier...
Autostart you can also do and many things more...
When I switch to Linux I thought about if it is possible just to switch power of without harddisc data corruption. With ext3 filesystem it is possible like in DOS!

But there ARE actually embedded motherboards with 4 serial ports, but not that cheap...

Rainer