NT Link vs. HostLink

[Supporter 1]

Hi, From a HMI point of view, which protocol is the better one, NT Link or HostLink? - What are the differences between these protocols? - Are there different user areas for the protocols? - Which protocol has best performance (based on that the HMI-application is developed properly (with consecutive addresses etc)). Thanks for your help, if you need more information please let me know. //Supporter

[james_applied 0]

I allways use NT-Link High speed.

[BobB 58]

No brainer - NT link is much faster.

[Michael Walsh 268]

I think it will be unanimous. NT-Link.

[Jay Anthony 118]

Why is it faster? Host Link is an ASCII protocol (two bytes per character.) NT Link is a binary protocol (one byte per character.) For every Hostlink character you get two NT Link characters. It also supports 115Kbits per second. Why is it better? Hostlink addresses the Omron Memory Map in words only. Nt Link addresses both in words and bits (that's why it is binary.) It can address a single bit in the Omron memory map. Why is it robust? It supports FINS (Factory Intelligent Network Service.) It is network transparent due to embedding routing of networked Omron PLCs. Why does Hostlink protocol exist? Born in 1978, there are many third party products and peripherals which still use Hostlink protocol. Anything else, I bow to PMCR.

[Michael Walsh 268]

Nice post Jay. I forgot about the other questions and only answered the "Which one is better?" question. I might add one more reason that NT-Link is better: (Correction: C-Mode) Host-link protocol was developed before the W memory area existed, so you cannot access W bits and words with Host link (see below). The W area is commonly used (by me anyway) for addressing buttons and lamps on the HMI. Edited 6 Feb 2012 by Michael Walsh

[Mark- 17]

Hi, This must be HMI specific. PeakHMI can access the WR area. From the help file: Register Name Prefix Examples Data Type --snip-- Work Area WR WRxxx, WRxxx.yy Word, double word, float, boolean

[Michael Walsh 268]

If PeakHMI is able to write to W bits / words using Host-link, then they are using CV-Mode host-link, which does have this capability. Another non-host-link option could be if this is a reference to using FINS commands with Ethernet comms. The NS HMI uses C-Mode Host-link which does NOT support reading and writing W bits or words.

[PMCR 66]

Peak HMI is using CV Mode Host Link, as opposed to C Mode Host Link, which is what the NS uses. CV Mode Hostlink is a FINS command wrapped up in a Host Link frame. It is still ASCII, so not as effiicient as NTLink, but CV Mode Host Link does access all the memory areas just like NT Link. Omron HMIs (the NS specifically), only implement Host Link (C Mode) for backward compatbility to older Omron PLCs such as C200H, CQM1, etc.

[BobB 58]

Citect can also access W and all other areas in the CJ/CS/CP PLCs but uses a FINS driver and hooks in through FINS Gateway - my preferred way of setting up comms to a SCADA system but this is digressing from my interprataion of the original question which I assume refers to touch screens as I am unaware of any other HMI which has NT Link available as it is a proprietary protocol? Correct me if I am wrong. If it is available to other manufacturers I would fail to understand why they woulkd use host link in preference to NT Link. Choosing NT Link to an Omron screen as opposed to host link is still a no brainer. The explanations from some who have inside information is really interesting - thank you guys. I knew it was faster but did not know why.

[PMCR 66]

Bob Yes, NT Link is a proprietary protocol. I agree with you FINS Gateway (and now SYSMAC Gateway) is the best comms middleware. SYSMAC Gateway 1.20 (latest version) is now Windows 7, 64 bit compliant.