On Sun, 17 Feb 2019 02:08:06 -0800 (PST), gnuarm.deletethisbit@gmail.com wrote:>I'm working to improve a test program for the hardware I use to test some boards I make. These boards are tested using a test fixture controlled over an RS-232 port from the PC. So I don't need to lug hardware around with me I emulate the test fixture on the same PC I run the test program. I need comm port emulation software that will emulate a bridge between two serial ports to connect the test program and the test fixture emulator. > >One I've been using is called, oddly enough, "Free Virtual Serial Ports". It is free to use, but only in a limited configuration which will do the job, but just barely. I have also noticed that if my programs are not closed properly (or some other cause) this bridge software will hang one of the ports. > >I don't want to emulate the serial port connection in my test fixture emulator because if I take the program down a lot while testing, I will have to continually restart both the test program and the emulator program. There are a few initialization steps that become tedious after doing them a few dozen times. > >Is there a serial port bridge program that works well and is not expensive?You might want to take a look at a logic analyzer. E.g. at banggood.com search for "USB logic analyzer 8ch" . There is an 8 channel one for $10, and there is a software download presumably with protocol analysis of various protocols, if I look at the documents. If you scroll a little down, there is a "8. infos download from here" which gets you a .rar file of 57M. In it are installers for various OSses (Win, Mac, Ubuntu), and PDFs. What I cannot determine is which input voltages it allows. Scrolling down further on that page are some FAQ from which I gather that it does not handle 12V, 3.3V and 1.8V , so presumably TTL level only (0 or +5V). In that case, you might need level converters such as from Maxim. There are also such things on Banggood, search for 3-5V RS232 to TTL converter, or equivalent. I don't have the analyzer myself, just stumbled across it. The price is certainly OK! Mat Nieuwenhoven
Serial Port Emulation
Started by ●February 17, 2019
Reply by ●February 18, 20192019-02-18
Reply by ●February 18, 20192019-02-18
On 2/18/19 4:49 AM, David Brown wrote:> On 18/02/2019 09:38, Tauno Voipio wrote: >> On 17.2.19 22:16, David Brown wrote: >>> On 17/02/2019 17:54, Tauno Voipio wrote: >>>> On 17.2.19 12:08, gnuarm.deletethisbit@gmail.com wrote: >>>>> I'm working to improve a test program for the hardware I use to test >>>>> some boards I make. These boards are tested using a test fixture >>>>> controlled over an RS-232 port from the PC. So I don't need to lug >>>>> hardware around with me I emulate the test fixture on the same PC I >>>>> run the test program. I need comm port emulation software that will >>>>> emulate a bridge between two serial ports to connect the test >>>>> program and the test fixture emulator. >>>>> >>>>> One I've been using is called, oddly enough, "Free Virtual Serial >>>>> Ports". It is free to use, but only in a limited configuration >>>>> which will do the job, but just barely. I have also noticed that if >>>>> my programs are not closed properly (or some other cause) this >>>>> bridge software will hang one of the ports. >>>>> >>>>> I don't want to emulate the serial port connection in my test >>>>> fixture emulator because if I take the program down a lot while >>>>> testing, I will have to continually restart both the test program >>>>> and the emulator program. There are a few initialization steps that >>>>> become tedious after doing them a few dozen times. >>>>> >>>>> Is there a serial port bridge program that works well and is not >>>>> expensive? >>>>> >>>>> Rick C. >>>>> >>>> >>>> Get a USB serial port adapter and a null modem cable, >>>> so the test program does see any difference. >>>> >>> >>> "Null modem cable" ? He doesn't need RS-232 converters and 9-pin >>> DSUBs here. A couple of USB to TTL Uart cables is what he needs, with >>> the wires tied together. >>> >>> <https://www.ftdichip.com/Products/Cables/USBTTLSerial.htm> >>> >>>> The virtual serial ports are probably more part of the >>>> problem set than part of the solution set. >>>> >> >> >> Most of the off-the-shelf USB serial dongles have the 9 pin connectors >> with RS-232 DTE signals, which do need null modem to connect together. >> > > I guess it depends on which shelf you look on :-) > > It is /many/ years since I have had need of an RS-232 serial dongle. > But TTL level UART to USB converters - we go through these at a high > rate. Adding standard RS-232 to a board is big and expensive - you need > RS-232 drivers and a bulky DSUB connector, and then the cables. Adding > a TTL level UART is practically free - you need the Tx and Rx pins on > the microcontroller (many of which have several UARTs - finding one > spare is not nearly the challenge it used to be), and you need a 3-pin > header. For convenience, when we have the space, we use a 6-pin header > that matches the FTDI cables. > > So /my/ shelf has lots of FTDI TTL-level UART cables - and a single > RS-232 dongle gathering dust in the corner. > >I think if you look at what is commercially available, the most common device is RS232 levels, not TTL, because most commercial devices you want to talk to that have an external connector us RS232 levels, TTL is mostly used internally or known very short distances. With the advent of things like the Raspberry Pi, Arduino, and the like, the TTL version is getting more common, but those still mostly show up in electronic specialty shops, while the RS232 version show up many more places (like the electronics department of office supply stores, or even hardware stores).
Reply by ●February 18, 20192019-02-18
On 18/02/2019 13:25, Richard Damon wrote:> On 2/18/19 4:49 AM, David Brown wrote: >> On 18/02/2019 09:38, Tauno Voipio wrote: >>> On 17.2.19 22:16, David Brown wrote: >>>> On 17/02/2019 17:54, Tauno Voipio wrote: >>>>> On 17.2.19 12:08, gnuarm.deletethisbit@gmail.com wrote: >>>>>> I'm working to improve a test program for the hardware I use to test >>>>>> some boards I make. These boards are tested using a test fixture >>>>>> controlled over an RS-232 port from the PC. So I don't need to lug >>>>>> hardware around with me I emulate the test fixture on the same PC I >>>>>> run the test program. I need comm port emulation software that will >>>>>> emulate a bridge between two serial ports to connect the test >>>>>> program and the test fixture emulator. >>>>>> >>>>>> One I've been using is called, oddly enough, "Free Virtual Serial >>>>>> Ports". It is free to use, but only in a limited configuration >>>>>> which will do the job, but just barely. I have also noticed that if >>>>>> my programs are not closed properly (or some other cause) this >>>>>> bridge software will hang one of the ports. >>>>>> >>>>>> I don't want to emulate the serial port connection in my test >>>>>> fixture emulator because if I take the program down a lot while >>>>>> testing, I will have to continually restart both the test program >>>>>> and the emulator program. There are a few initialization steps that >>>>>> become tedious after doing them a few dozen times. >>>>>> >>>>>> Is there a serial port bridge program that works well and is not >>>>>> expensive? >>>>>> >>>>>> Rick C. >>>>>> >>>>> >>>>> Get a USB serial port adapter and a null modem cable, >>>>> so the test program does see any difference. >>>>> >>>> >>>> "Null modem cable" ? He doesn't need RS-232 converters and 9-pin >>>> DSUBs here. A couple of USB to TTL Uart cables is what he needs, with >>>> the wires tied together. >>>> >>>> <https://www.ftdichip.com/Products/Cables/USBTTLSerial.htm> >>>> >>>>> The virtual serial ports are probably more part of the >>>>> problem set than part of the solution set. >>>>> >>> >>> >>> Most of the off-the-shelf USB serial dongles have the 9 pin connectors >>> with RS-232 DTE signals, which do need null modem to connect together. >>> >> >> I guess it depends on which shelf you look on :-) >> >> It is /many/ years since I have had need of an RS-232 serial dongle. >> But TTL level UART to USB converters - we go through these at a high >> rate. Adding standard RS-232 to a board is big and expensive - you need >> RS-232 drivers and a bulky DSUB connector, and then the cables. Adding >> a TTL level UART is practically free - you need the Tx and Rx pins on >> the microcontroller (many of which have several UARTs - finding one >> spare is not nearly the challenge it used to be), and you need a 3-pin >> header. For convenience, when we have the space, we use a 6-pin header >> that matches the FTDI cables. >> >> So /my/ shelf has lots of FTDI TTL-level UART cables - and a single >> RS-232 dongle gathering dust in the corner. >> >> > > I think if you look at what is commercially available, the most common > device is RS232 levels, not TTL, because most commercial devices you > want to talk to that have an external connector us RS232 levels, TTL is > mostly used internally or known very short distances.RS-232 is short distance too (though a bit longer than TTL) - for long distances you use RS-485 or RS-422. RS-232 is a legacy standard - there is plenty of old stuff the still has it, but it would be a strange choice for anything new.> > With the advent of things like the Raspberry Pi, Arduino, and the like, > the TTL version is getting more common, but those still mostly show up > in electronic specialty shops, while the RS232 version show up many more > places (like the electronics department of office supply stores, or even > hardware stores). >It is so many years since RS-232 has been in common use that I'd be surprised to find many real shops stocking dongles. But I agree that you are more likely to find one in a big computer shop than to find a TTL level UART dongle. However, this is comp.arch.embedded, and people here will already have shops, suppliers, webshops, etc., for which TTL level cables are on stock.
Reply by ●February 18, 20192019-02-18
On Monday, February 18, 2019 at 4:49:07 AM UTC-5, David Brown wrote:> On 18/02/2019 09:38, Tauno Voipio wrote: > > On 17.2.19 22:16, David Brown wrote: > >> On 17/02/2019 17:54, Tauno Voipio wrote: > >>> On 17.2.19 12:08, gnuarm.deletethisbit@gmail.com wrote: > >>>> I'm working to improve a test program for the hardware I use to test > >>>> some boards I make. These boards are tested using a test fixture > >>>> controlled over an RS-232 port from the PC. So I don't need to lug > >>>> hardware around with me I emulate the test fixture on the same PC I > >>>> run the test program. I need comm port emulation software that will > >>>> emulate a bridge between two serial ports to connect the test > >>>> program and the test fixture emulator. > >>>> > >>>> One I've been using is called, oddly enough, "Free Virtual Serial > >>>> Ports". It is free to use, but only in a limited configuration > >>>> which will do the job, but just barely. I have also noticed that if > >>>> my programs are not closed properly (or some other cause) this > >>>> bridge software will hang one of the ports. > >>>> > >>>> I don't want to emulate the serial port connection in my test > >>>> fixture emulator because if I take the program down a lot while > >>>> testing, I will have to continually restart both the test program > >>>> and the emulator program. There are a few initialization steps that > >>>> become tedious after doing them a few dozen times. > >>>> > >>>> Is there a serial port bridge program that works well and is not > >>>> expensive? > >>>> > >>>> Rick C. > >>>> > >>> > >>> Get a USB serial port adapter and a null modem cable, > >>> so the test program does see any difference. > >>> > >> > >> "Null modem cable" ? He doesn't need RS-232 converters and 9-pin > >> DSUBs here. A couple of USB to TTL Uart cables is what he needs, with > >> the wires tied together. > >> > >> <https://www.ftdichip.com/Products/Cables/USBTTLSerial.htm> > >> > >>> The virtual serial ports are probably more part of the > >>> problem set than part of the solution set. > >>> > > > > > > Most of the off-the-shelf USB serial dongles have the 9 pin connectors > > with RS-232 DTE signals, which do need null modem to connect together. > > > > I guess it depends on which shelf you look on :-) > > It is /many/ years since I have had need of an RS-232 serial dongle. > But TTL level UART to USB converters - we go through these at a high > rate. Adding standard RS-232 to a board is big and expensive - you need > RS-232 drivers and a bulky DSUB connector, and then the cables. Adding > a TTL level UART is practically free - you need the Tx and Rx pins on > the microcontroller (many of which have several UARTs - finding one > spare is not nearly the challenge it used to be), and you need a 3-pin > header. For convenience, when we have the space, we use a 6-pin header > that matches the FTDI cables. > > So /my/ shelf has lots of FTDI TTL-level UART cables - and a single > RS-232 dongle gathering dust in the corner.The RS-232 adapters are much easier to locate. RS-232 is not hard to add to any circuit, it's just one chip and a very common chip at that. Adding yet another special connector that has to be documented and shown to an operator is even more work. The DB-9 serial port connector is still very common and not used for much else so hard to mix up with anything else. My only regret is not using a right angle connector on the board so the cable didn't stick up in the air, but rather laid flat. But none of that is important at this point. I found the com0com software that lets me use the test fixture emulator without any hardware at all, including the USB serial port adapters. Yea! Rick C.
Reply by ●February 18, 20192019-02-18
On 2019-02-18 David Brown wrote in comp.arch.embedded:> > header. For convenience, when we have the space, we use a 6-pin header > that matches the FTDI cables.That's what we do as well if space allows it! Just so much easier to order an FTDI cable from (for example) Farnell and plug it straight in instead of having to mount your own connector.> So /my/ shelf has lots of FTDI TTL-level UART cables - and a single > RS-232 dongle gathering dust in the corner.I use both types quite often. -- Stef (remove caps, dashes and .invalid from e-mail address to reply by mail) "Ninety percent of baseball is half mental." -- Yogi Berra
Reply by ●February 19, 20192019-02-19
On 2019-02-18, David Brown <david.brown@hesbynett.no> wrote:> > RS-232 is short distance too (though a bit longer than TTL) - for long > distances you use RS-485 or RS-422. RS-232 is a legacy standard - there > is plenty of old stuff the still has it, but it would be a strange > choice for anything new.I'm genuinely interested to hear people thoughts on this. Personally if I anticipate a true long life interfacing requirement - 20, 30, 40 years - RS232 is my preferred option, ideally (if appropriate to the use case) with a command line on it. My rationale has always been that RS232 isn't going anywhere, terminal emulators are always going to be around, so that combination makes fewest assumptions about hardware or software. Even if serial ports are no longer standard equipment they'll always be easy enough to add and at moderate cost. The relative simplicity of the technology and the simplicity of the host software makes me feel sure of that. It's also what's always made me feel slightly uneasy about USB. In many ways it is a nice standard but it depends on quite a thick layer of software on the host side. If it falls out of favour and support gets dropped over time re-adding that software layer is problematic even if the hardware is to hand. It may seem difficult to imagine now but I can see it coming - try reading the original USB spec and seeing what a big play it makes of the single cable with just one upstream and one downstream connector. Now there are so many possible combinations of port and cable it makes parallel SCSI look posivitely straightforward. And yes, I do see this creating confusion among non-technical users: the original B plug has been poorly recognised for years, and I've heard a few people recently see an A plug and respond along the lines of "No, that's a charger plug, I need a _USB_ plug...". Full size A sockets are already disappearing from laptops, in a few years someone is bound to drop USB entirely in favour of something else to "improve" things for the consumer. The software issue is similar for the other hardware that I can't see disappearing, namely ethernet. Specific media may change in popularity but you should be able to interface older stuff easy enough, just as it still isn't _too_ difficult to track down a 10Mbit hub with AUI and/ BNC connectors if you need modern stuff to connect to coax. My concern there it that we'll be transitioning to IPv6 any decade now. Realistically when is imposssible to predict but I feel sure once a certain critical mass develops IPv4 will seem obsolete in 5-10 years. If we use that in our though processes large amount of equipment and plant may well not be even halfway through its expected life when that timespan elapses. Dual stack is one possibilty but I'll admit I don't understand IPv6 well enough yet and I don't like the sound of the complexity. I don't pretend to have answers in the general case, just interested in what peoples thoughts are. -- Andrew Smallshaw andrews@sdf.org
Reply by ●February 19, 20192019-02-19
On Tuesday, February 19, 2019 at 11:10:16 AM UTC-5, Andrew Smallshaw wrote:> On 2019-02-18, David Brown <david.brown@hesbynett.no> wrote: > > > > RS-232 is short distance too (though a bit longer than TTL) - for long > > distances you use RS-485 or RS-422. RS-232 is a legacy standard - there > > is plenty of old stuff the still has it, but it would be a strange > > choice for anything new. > > I'm genuinely interested to hear people thoughts on this. Personally > if I anticipate a true long life interfacing requirement - 20, 30, > 40 years - RS232 is my preferred option, ideally (if appropriate > to the use case) with a command line on it. My rationale has always > been that RS232 isn't going anywhere, terminal emulators are always > going to be around, so that combination makes fewest assumptions > about hardware or software. Even if serial ports are no longer > standard equipment they'll always be easy enough to add and at > moderate cost. The relative simplicity of the technology and the > simplicity of the host software makes me feel sure of that. > > It's also what's always made me feel slightly uneasy about USB. > In many ways it is a nice standard but it depends on quite a thick > layer of software on the host side. If it falls out of favour and > support gets dropped over time re-adding that software layer is > problematic even if the hardware is to hand.You raise some interesting points. I don't know how easy it is to add RS-232 to a PC other than through a USB interface which adds back all those layers of software even if you don't need to deal with them. The last RS-232 board I've seen was for the PCI bus which is no longer used in PCs. Even so, desktops are waining and laptops are sold in much greater numbers. I wouldn't design anything that required a desktop to work. So I think you are stuck with USB either as the actual interface or an intermediate interface.> It may seem difficult to imagine now but I can see it coming - try > reading the original USB spec and seeing what a big play it makes > of the single cable with just one upstream and one downstream > connector. Now there are so many possible combinations of port > and cable it makes parallel SCSI look posivitely straightforward. > And yes, I do see this creating confusion among non-technical users: > the original B plug has been poorly recognised for years, and I've > heard a few people recently see an A plug and respond along the > lines of "No, that's a charger plug, I need a _USB_ plug...". Full > size A sockets are already disappearing from laptops, in a few > years someone is bound to drop USB entirely in favour of something > else to "improve" things for the consumer.I think there is nothing any other interface can do better than USB other than possibly wireless. USB is fast and stable and here for the long haul. Heck, it has ramped up from 1.0 to 1.1, 2.0, 3.0, 3.1... what is going to replace it? The type C connector is a significant improvement and with enough time will become the dominant interface although I think displacing the type A connector will take a long time. As you say, it's a charger defacto interface.> The software issue is similar for the other hardware that I can't > see disappearing, namely ethernet. Specific media may change in > popularity but you should be able to interface older stuff easy > enough, just as it still isn't _too_ difficult to track down a > 10Mbit hub with AUI and/ BNC connectors if you need modern stuff > to connect to coax. My concern there it that we'll be transitioning > to IPv6 any decade now. Realistically when is imposssible to > predict but I feel sure once a certain critical mass develops IPv4 > will seem obsolete in 5-10 years. If we use that in our though > processes large amount of equipment and plant may well not be even > halfway through its expected life when that timespan elapses. Dual > stack is one possibilty but I'll admit I don't understand IPv6 well > enough yet and I don't like the sound of the complexity.It's dual stack now. There is nothing that will make IPv4 become inoperable. Just as the routers hide the IP address of local devices, IPv6 can be used in the entire rest of the world and IPv4 can be used locally.> I don't pretend to have answers in the general case, just interested > in what peoples thoughts are.I expect USB will survive for decades more even if only to interface to mice and printers. In fact, newer laptops seem to have more USB connectors with many having four while the typical number used to be three. I'm just glad the PCMCIA interface is gone. Rick C.
Reply by ●February 19, 20192019-02-19
On Tue, 19 Feb 2019 16:10:12 -0000 (UTC), Andrew Smallshaw <andrews@sdf.org> wrote:>On 2019-02-18, David Brown <david.brown@hesbynett.no> wrote: >> >> RS-232 is short distance too (though a bit longer than TTL) - for long >> distances you use RS-485 or RS-422. RS-232 is a legacy standard - there >> is plenty of old stuff the still has it, but it would be a strange >> choice for anything new.The problem with both TTL and RS-232 is the ground potential issues. Any ground potential noise will directly deteriorate the noise margins. High speed RS-232 is also problematic, since the impedance levels are too high for typical cable impedances. No such problems with RS-422/485, but of course common mode voltage range must be considered and galvanic isolation may be needed.>I'm genuinely interested to hear people thoughts on this. Personally >if I anticipate a true long life interfacing requirement - 20, 30, >40 yearsLooking back, RS-232 and 20 mA was popular. The nice thing about current loops was that you nearly always had galvanic isolation (relays, optoisolators).>40 years - RS232 is my preferred option, ideally (if appropriate >to the use case) with a command line on it. My rationale has always >been that RS232 isn't going anywhere, terminal emulators are always >going to be around, so that combination makes fewest assumptions >about hardware or software. Even if serial ports are no longer >standard equipment they'll always be easy enough to add and at >moderate cost. The relative simplicity of the technology and the >simplicity of the host software makes me feel sure of that.<Skipped about USB>>The software issue is similar for the other hardware that I can't >see disappearing, namely ethernet. Specific media may change in >popularity but you should be able to interface older stuff easy >enough, just as it still isn't _too_ difficult to track down a >10Mbit hub with AUI and/ BNC connectors if you need modern stuff >to connect to coax.These days, many even small microcontrollers have Ethernet interface. In a simplest cases just use raw MAC frames or UDP . Surprisingly small micros have web servers, so they have at least a rudimentary TCP stack.>My concern there it that we'll be transitioning >to IPv6 any decade now. Realistically when is imposssible to >predict but I feel sure once a certain critical mass develops IPv4 >will seem obsolete in 5-10 years. If we use that in our though >processes large amount of equipment and plant may well not be even >halfway through its expected life when that timespan elapses. Dual >stack is one possibilty but I'll admit I don't understand IPv6 well >enough yet and I don't like the sound of the complexity.The ARP (Address Resolution Protocol) program for mapping between MAC and IPv4 addresses is less than one page long, the MAC to IPv6 mapping shouldn't be much more complex.>I don't pretend to have answers in the general case, just interested >in what peoples thoughts are.
Reply by ●February 19, 20192019-02-19
On Tue, 19 Feb 2019 09:12:14 -0800 (PST), gnuarm.deletethisbit@gmail.com wrote:>On Tuesday, February 19, 2019 at 11:10:16 AM UTC-5, Andrew Smallshaw wrote: >> On 2019-02-18, David Brown <david.brown@hesbynett.no> wrote: >> > >> > RS-232 is short distance too (though a bit longer than TTL) - for long >> > distances you use RS-485 or RS-422. RS-232 is a legacy standard - there >> > is plenty of old stuff the still has it, but it would be a strange >> > choice for anything new. >> >> I'm genuinely interested to hear people thoughts on this. Personally >> if I anticipate a true long life interfacing requirement - 20, 30, >> 40 years - RS232 is my preferred option, ideally (if appropriate >> to the use case) with a command line on it. My rationale has always >> been that RS232 isn't going anywhere, terminal emulators are always >> going to be around, so that combination makes fewest assumptions >> about hardware or software. Even if serial ports are no longer >> standard equipment they'll always be easy enough to add and at >> moderate cost. The relative simplicity of the technology and the >> simplicity of the host software makes me feel sure of that. >> >> It's also what's always made me feel slightly uneasy about USB. >> In many ways it is a nice standard but it depends on quite a thick >> layer of software on the host side. If it falls out of favour and >> support gets dropped over time re-adding that software layer is >> problematic even if the hardware is to hand. > >You raise some interesting points. I don't know how easy it is to add RS-232 to a PC other than through a USB interface which adds back all those layers of software even if you don't need to deal with them. The last RS-232 board I've seen was for the PCI bus which is no longer used in PCs.It is very easy with Ethernet to RS-232/422/485 converters. I have used 1, 2, 4 and 8 line Moxa serial line converters and I think 16 line modules are also available. Just point Telnet to the converter IP-address and use it as Hyperterminal :-). A large system had one Ethernet cable feeding seven 8 line Eth(RS-232 converters feeding 50 RS-232 to current loop converters controlling 50 legacy devices. Early smaller systems used a few dozen serial lines directly from two PCI RS.232 cards. That was a nasty bundle of serial cables coming out of the PC :-), but the largest system had only one additional Ethernet port.>Even so, desktops are waining and laptops are sold in much greater numbers. I wouldn't design anything that required a desktop to work. So I think you are stuck with USB either as the actual interface or an intermediate interface.Better design for smart phone controllability. That would be wireless and Ethernet.
Reply by ●February 19, 20192019-02-19
On 2019-02-19, upsidedown@downunder.com <upsidedown@downunder.com> wrote:>>You raise some interesting points. I don't know how easy it is to >>add RS-232 to a PC other than through a USB interface which adds >>back all those layers of software even if you don't need to deal >>with them. The last RS-232 board I've seen was for the PCI bus >>which is no longer used in PCs.There are still plenty of choices for PCI-express serial boards (up to 32-ports per board): https://comtrol.com/products/rocketport-multi-port-serial-cards/rocketport-express> It is very easy with Ethernet to RS-232/422/485 converters. I have > used 1, 2, 4 and 8 line Moxa serial line converters and I think 16 > line modules are also available. Just point Telnet to the converter > IP-address and use it as Hyperterminal :-).They're generally available with up to 32 ports: https://comtrol.com/products/devicemaster-ethernet-device-servers Disclaiming: my employer makes the PCI-express boards and Ethernet attached serial ports linked to above, and I maintain Linux drivers for them and the firmware for the Ethernet-attached products. [The Linux drivers all support up to 256 ports.] That said, modern USB-attached serial ports all seem to work fine. At least under Linux, the kernel has had built-in drivers for all the popular chipsets for decades. -- Grant Edwards grant.b.edwards Yow! Like I always say at -- nothing can beat gmail.com the BRATWURST here in DUSSELDORF!!
