Reliable Com Ports

[Colin Carpenter 10]

Five or six years ago, I installed a PC running Windows NT with a SCADA system that currently "talks" to three separate serial ports, each one of which talks to a RS232/RS485 converter which then "talk" to a Mitsubishi, a Field, and a Modbus multidrop loop. The company want to upgrade the PC to a newer Windows XP machine, but the PC hardware only allows for half height PCI cards, and, in common with most modern PCs, it doesn't even have one serial port available. I know that there are "good and bad" com port solutions out there, so could anyone please tell me if they have had good experiences with a solution to add three serial ports to one modern PC. I assume that USB is the easiest way, but also know that some work and some don't. Thanks.

[Crossbow 297]

Mitsubishi recommends the Keyspan USA-19 USB to serial adapter. It works with all of their current software. Personally I use a CP Technologies CP-US-03 USB to serial adapter with Mitsubishi and several other vendors. But for many ports, I would recommend looking at some kind of Digiboard. They make them with 2, 4, or 8 ports. I haven't had to use one in years, but that's an option.

[Colin Carpenter 10]

Thanks, those Digiboard options look pretty good, though pretty expensive. I remember the days when a 1 MB of ram cost £25 and serial cards were £5, now 256MB of ram costs £17, and serial cards are about £300. Times change.

[netdomain 0]

Just buy a PCI card with 8 Serial Ports. Amazon is selling one for $118 USD. You might find it cheaper other places. here's the link http://www.amazon.com/8-Port-Pci-Serial-Card/dp/B0006TLENC

[JRoss 84]

If this is an unattended computer that you need to collect data, I highly recommend getting PCI serial cards like this one (quick search on Google, feel free to shop around). Make sure to search for "half-height" so you find something that will fit. The reason being that a USB to Serial adapter can be flaky, which is why some work and others don't. Even the ones that work can be temperamental. For instance, I've found that letting my computer go into standby with the Mitsubishi Servo software running causes my computer to lock up. I have been told that's because I'm using a USB-to-serial adapter. I've since gotten a PCMCIA card for my laptop, but haven't tested it with that software. Now this may be because Mitsu didn't write their software to handle that properly, but on the other hand, who does? I'd also recommend using single-port serial cards, so that if one blows, you can replace it. Also, my two-port PCMCIA card has a tendency to swap COMs every startup. It's set for COM1 and COM2, but I never know which is which!

[panic mode 246]

imho priority with pc hardware selection goes first to the cards and then PC that will serve as host, not the other way around but there are ethernet based devices with four RS232 ports. personally first thing I look at is the isolation (got burned few times with PC locking up, we install some 30-50 PCs a year, each is part of custom machine, different from previous one...). we used LAVA cards and many other brands. they all worked fine with older PCs. newer PCs are much too sensitive for experimenting with something in industrial setting (there are things inside PC are running at only 1.2V or so and everything is part of the chipset anyway, dedicated multiport cards are also just one big chip running at low voltage with internal memory etc. this stuff is NOT to be underestimated - it will bite you when you least expect). the only TRULY isolated multiport comm cards i came accross are from Meilhaus. 4-port unit like ME9100C/42 was about $600. eight port version like ME9100C/82 was only $100 more. all other brands and models i came accross are only isolating two signals (Rx/Tx but not handhake lines). Nowdays also B&B makes isoalted USB to RS232 converters for about $100-120 each but they are single port (not sure if they have multiport). Bad thing about USB to RS232 converters is that they keep migrating from one to another port every time they are plugged to different USB port. either label everything nicely of good luck explaining over the phone how to fix things once they pulled one or more cables by "accident". I haven't try that one yet but we try avoid USB devices for installations because so many of them have that random blip that normally doesn't cause any issues but then they do it when not expected. This includes need to be plugged after PC is booted or in case of comm card occasional one or two random characters at powerup. Many such things are not an issue - most of the time but manufacturers of USB devices are far from being perfect... www.meilhaus.de (they have distrubutors everywhere, in USA it's ICS). also check Moxa external Ethernet to 4xRS232 port server http://www.moxa.com/product/NPort_5410.htm