UART Question... - PLCS.net

Eric Nelson · May 26th, 2002, 10:14 PM

I'm getting tired of the constant cable-swapping zzzzz so I'm adding a few additional serial ports to my desktop (Having only 2 just doesn't cut it anymore).

While shopping around, I see that I have a choice of specifying 16550, 16650, or 16850 UARTs. Of course, as the size of the buffer goes up, so does the cost.

I only use these serial ports for communication to PLCs, HMIs, servo drives, etc. (you know, the stuff we program for a living), and rarely need to exceed 19.2 kbps.

So my question is: Does it really make a difference which UART I choose? IOW, are there any advantages (that I'll notice?) by having a larger buffer?

With the lack of Legacy ports on many new laptops, there's been a lot of confusion as to which serial adapters (USB and PCMCIA) are compatible with which PLC hardware. Though my question shouldn't be related to this, I just don't want to get stuck with a useless serial card. mddr

TIA for any input,

-Eric

Ken Roach · May 27th, 2002, 12:05 AM

If you're connecting to Allen-Bradley products, especially if you're going to attempt the 1747-PIC driver in RSLinx, go with good old 16550 UARTs.

The biggest serial port expander I've seen tested was just a 4-port PCI expander. RSLinx handled those 4 ports fine.

I use an older Quatech 2-port PCMCIA card and its performance has been perfect with all applications (RSLinx and many ASCII and Modbus utilities) I've tried on it.

rsdoran · May 27th, 2002, 12:40 AM

The thing you gotta watch out for is being capable of using more serial ports. A serial port needs an IRQ, do you have 2 more that you can allocate.

I know, you can use a PCI card that "should" eliminate that problem. Verify that everything will comply.

You didnt mention 16750 or 16950...shouldnt matter overall, they "should" be backward compatible. If you dont see a need for faster than 57.6kps than stick with a standard card but from the prices I have seen checkout if the 16750 and up can go below 115k, if so there is no reason not to try one.

http://www.byterunner.com/why.html

http://www.quatech.com/

Both those sites have info on the chips and cards.

Eric Nelson · May 28th, 2002, 09:06 PM

Thanks Guys.... Exactly the responses I was looking for.

Just so happens I was looking at Quatech stuff!

beerchug

-Eric

P.S. Ron, that byterunner link was very informative!

May 26th, 2002, 10:14 PM	#1
Eric Nelson Lifetime Supporting Member + Moderator Join Date: Apr 2002 Location: Randolph, NJ Posts: 4,070	UART Question... I'm getting tired of the constant cable-swapping zzzzz so I'm adding a few additional serial ports to my desktop (Having only 2 just doesn't cut it anymore). While shopping around, I see that I have a choice of specifying 16550, 16650, or 16850 UARTs. Of course, as the size of the buffer goes up, so does the cost. I only use these serial ports for communication to PLCs, HMIs, servo drives, etc. (you know, the stuff we program for a living), and rarely need to exceed 19.2 kbps. So my question is: Does it really make a difference which UART I choose? IOW, are there any advantages (that I'll notice?) by having a larger buffer? With the lack of Legacy ports on many new laptops, there's been a lot of confusion as to which serial adapters (USB and PCMCIA) are compatible with which PLC hardware. Though my question shouldn't be related to this, I just don't want to get stuck with a useless serial card. mddr TIA for any input, -Eric

May 27th, 2002, 12:40 AM	#3
rsdoran Lifetime Supporting Member Join Date: Apr 2002 Location: Birmingham, AL Posts: 7,372	The thing you gotta watch out for is being capable of using more serial ports. A serial port needs an IRQ, do you have 2 more that you can allocate. I know, you can use a PCI card that "should" eliminate that problem. Verify that everything will comply. You didnt mention 16750 or 16950...shouldnt matter overall, they "should" be backward compatible. If you dont see a need for faster than 57.6kps than stick with a standard card but from the prices I have seen checkout if the 16750 and up can go below 115k, if so there is no reason not to try one. http://www.byterunner.com/why.html http://www.quatech.com/ Both those sites have info on the chips and cards. __________________ http://www.patchn.com Industrial Electrical & Maintenance @ www.patchn.com "Tell me and I forget, show me and I remember, involve me and I understand."

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May 27th, 2002, 12:05 AM	#2
Ken Roach Lifetime Supporting Member + Moderator Join Date: Apr 2002 Location: Seattle, WA Posts: 8,563	If you're connecting to Allen-Bradley products, especially if you're going to attempt the 1747-PIC driver in RSLinx, go with good old 16550 UARTs. The biggest serial port expander I've seen tested was just a 4-port PCI expander. RSLinx handled those 4 ports fine. I use an older Quatech 2-port PCMCIA card and its performance has been perfect with all applications (RSLinx and many ASCII and Modbus utilities) I've tried on it.

May 28th, 2002, 09:06 PM	#4
Eric Nelson Lifetime Supporting Member + Moderator Join Date: Apr 2002 Location: Randolph, NJ Posts: 4,070	Thanks Guys.... Exactly the responses I was looking for. Just so happens I was looking at Quatech stuff! beerchug -Eric P.S. Ron, that byterunner link was very informative!

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