Created Date: December 19,2011

Created by: Do-more PE

It depends on what your goals are. Both utilize the same format, the Ethernet packet is essentially just a serial packet with a TCP wrapper. For the most part Serial over Ethernet is a personal preference, but I will break down the pros and cons for each for you to try to help you out.

Pros:

Ethernet - Easy to wire. Good speed and data throughput. Easy to configure. Wiring and connectors are easy to find.

Serial - It is more deterministic than Ethernet, you know that once you send the packet it will be at the end device right away. Fairly easy to configure. Speed can be good and occasionally faster than Ethernet at high baud rates.

Cons:

Ethernet - Non-deterministic, once you send the packet it may take a while to get there depending on the network configuration.

Serial - Speed is dependent on various factors including baud rate supported by both devices, noise, etc. Wiring can be a hassle, correct wire type is needed.

With that being said, I always advise people to put Ethernet coms to devices that are being controlled onto their own network. This cuts down on the non-deterministic side of Ethernet and helps to insure that packets have as little delay as possible. Personally, I use Ethernet whenever possible because I dislike troubleshooting serial problems. Ethernet just works.

Created Date: December 21,2011

Created by: jackson

If you go with Ethernet and you don't have any specific personal preference between the PAC 3000 and the Direct Logic series, I would choose the PAC.

The way it performs Ethernet communications is more efficient (faster) than the way Direct Logic does it.

The PAC 3000 can/will send concurrent requests to multiple devices on the Ethernet network where the Direct Logic can only complete 1 transaction to a device at a time.

The PAC also has a few more features/flexibility with Modbus TCP over the Direct Logic.

Just my opinion....

Created Date: December 24,2011

Created by: clasentech

I was very disappointed in the speeds of the comms between my 2 Emerson Servos and my DL260 with a ECOM100 (TCP). You can only do one comm per scan. So if your scan time is 50 ms and you have 10 drives you need to constantly poll a read and a write that means you only get back to the original/first read (or write) after 1 full second. I would guess that in my application serial would be just as fast and of course cheaper. Also the Ibox for RTU are sweet and there arn't any for the TCP with the drives. The code looks odd with the conversions you have to do.

Created Date: February 28,2012

Created by: bfitz

No. Traditional Ethernet by default is non-deterministic and there is no way to change that. Here is a link that describes why Ethernet is non-deterministic.

The next page of your link describes how to set up a deterministic Ethernet network. They use full duplex switches. They also have a pretty picture :) .

Brian

Created Date: December 19,2011

Created by: ezfx

Hello,

I'm trying to decide what CPU to use in regards to Modbus communication, and I'm having a hard time understanding what the difference is between them.

The DL 260 has only RTU and the PAC 3000 has TCP and RTU, but at a higher cost, I do know that RTU is serial thru 485, and TCP is Ethernet but cant really understand the difference.

I will be controlling 9 Emerson servo drives, and will also use a C-more touch panel.

So I would like to know what is the advantage in using TCP vs RTU for my operation. ( if there is one)

Is there any speed difference?

Thanks Gerry