USB or Serial on the controller

Operaghost · Oct 4, 2009

So, what if your controller could only have a USB or serial connection but not both.

For years we have been dealing with serial ports and we have products and interfaces galore using those serial ports. If you had to select between a controller that had USB or serial but not both built-in, which would you choose.

What would be the downside if you choose the USB only version?

OG

Peter Nachtwey · Oct 4, 2009

I like USB

The only downside is the cable length is limited. That doesn't make any difference in my office but I bet it does to people in the field. This forces them to be close, within 5 meters, to the controllers.

Serial ports and cables are a support problem. Too many people try to make their own serial cables and can't do it so they call us and ask why they can't talk to our controllers when they should have bought a $10-15 pre made null modem cable from Radio Shack and saved us $30 worth of time.

That isn't a problem with USB cables because they are pre made.

USB transfer speeds are also MUCH faster and efficient than serial ports. More data gets sent per packet or interrupt using USB.

danw · Oct 4, 2009

Well, a controller port can be either used for
- configuration/programming
- troubleshooting
- HMI comm
- data comm
- remote communications for all the above via modem

I'm guessing that a controller with only one port is market targeted at the low end. At that low end remote comm might be a niche worth sacrificing.

But isn't HMI comm a high percentage of installations? What percentage of PLCs install blind nowadays?

I'm not sure the HMI market is USB ready.

For a strictly local programming connection, I love the ease and speed of USB. But USB-only might hamper viability of HMI comm.

geniusintraining · Oct 4, 2009

Mitsubishi is trying... the GOT 1000's (HMI) have a USB port on the front so you don't need to open the panel to hook up to the HMI, the Q series PLC's have a USB port built in to the CPU

The new Automation Direct PLC's also have the USB port on on the CPU, I think the market is moving toward USB's as a standard.

Operaghost · Oct 4, 2009

Ok, so I didn't intend for this to be a "Vendor A does this" thread.

I'm also not necessarily saying that the controller/system couldn't have Ethernet too. It is strictly USB vs Serial that I am curious about. What impact do you see if you could only use one.

I had forogtten about the distance limit of USB. That certainly could be a factor.

OG

SMOKE · Oct 5, 2009

Peter is a vendor. You almost can't buy a PC with a serial port. USB is how you should go (mostly to configure the Ethernet/IP). I actually wish there was a preset standard IP address. Since AB came up with it every Ethernet product should come pre-setup with an IP of 192.168.0.1.

rdrast · Oct 5, 2009

SMOKE said:
I actually wish there was a preset standard IP address. Since AB came up with it every Ethernet product should come pre-setup with an IP of 192.168.0.1.

Err...No.

chud · Oct 5, 2009

does mac addres ring a bell smoke?

geniusintraining · Oct 5, 2009

Operaghost said:
Ok, so I didn't intend for this to be a "Vendor A does this" thread.

I wasn't about to go there.... my point was that a lot of vendors are moving in that direction already and I think others will soon and that will be the norm.

I have a few USB repeaters... they are about 3 meters long, not sure how they would work if you chained them together

JesperMP · Oct 5, 2009

Re serial or USB.

Can I chose "neither" ?

henry5674 · Oct 5, 2009

I agree with the previous post "Neither" put ethernet in there instead. I use the new mitsubishi Q series which have built in USB and Ethernet. Very flexible. If i need RS232 comms i just slip a RS232 card in the rack.
but if i had to choose I would rather go for the RS232 because it is much more flexible even though the speeds are painful.

Operaghost · Oct 5, 2009

So part of what I was thinking when I started this thread was the loss of a serial port and how often that serial port is used for things other than a programming port. Things like:

Interfacing systems from different vendors
Connection to an HMI
ASCII input or output
Connections to legacy systems

With USB I would think that those options would have to be handled using an alternate communications method such as Ethernet.

Are we still using the serial port for anything other than a programming port?

OG

geniusintraining · Oct 5, 2009

Operaghost said:
Are we still using the serial port for anything other than a programming port?

Yes... and other then HMI connection, I have done a lot of other (data display's) but I also think in the big picture its a small portion... most vendors sell some form of serial add on to the PLC's, so yes I think we could get rid of the serial but still need an option of a serial module

Fast track and other sigma tools are big into feed back such as tact time, this can be easily displayed with a serial port and a cheap display... but I have also done this over the ethernet

JesperMP · Oct 5, 2009

You guys are forgetting something,
Serial could be interconnected any which way.(edit: as long as the partners had male ports, and the cable was crossed)
With USB you must chose USB A (host) or USB B (device).
Which one do you have in mind ?
No matter if you chose USB A or B, it excludes the "interconnecting" part.

Besides, there does not exist a standardized way of simply exchanging data via USB. If the PLC is a USB B device, then you need a windows driver to connect to it from your PC, or HMI, or whatever. That driver can only come from the original vendor, which effectively excludes 3rd party vendors. Do you want that ?

The best attempt at establishing a universal and open standard for data exchange is OPC UA, and this more or less demands an ethernet connection.

S7Guy · Oct 5, 2009

If I had to choose between USB and serial, I would use a different device. USB was cool in 1998 when an ethernet adapter was still an option in many PCs, but in 2009, it just doesn't bring much to the table. Even with serial, I would be able to use a ethernet to serial adapter 99% of the time.

USB or Serial on the controller

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