I may be wrong, but I should think using WinCC Professional (rather than WinCC Unified) might work better for communicating with an S5-PLC.

Also, WinCC Professional may be considerably more similar to the Lauer interface since it is based on WinCC Flex, which is much closer to HMIs designed to communicate with S5 PLCs.

Contact your local Siemens Distributor for a more hands-on getting started session and meet with an applications engineer who might get you going in the right direction very quickly.

In the meantime, I would urge you to submit a Support Request to Siemens Support stating the very same details shared in your original post here.  LINK: https://sieportal.siemens.com/en-us/mysieportal/support-requests/create 

I am assuming you have the original S5 program source, the Lauer PCS900 project source, and are familiar with the notion of non-symbolic addressing of DB and other tag data (the default/standard for S5 and S7-300/400 PLCs).

If there are tools that allow exporting the current HMI configuration to text (or xml) files, you can possibly manipulate those exported files into compatible files for importing into WinCC, like HMI-only tags, and PLC addresses accessed by the HMI, along with the type of access: Read/Write/Read-Write

Those types of things may save you time, improve consistency, and also enable HMI/PLC referenced tag name changes you wish had been done years ago, but left alone for historical purposes (or was mandated).

0. Find out whether WinCC Pro or WinCC Unified is right for communicating with an S5 PLC, using  _only_ absolute addressing (from either 1/2/3 below)
1. Create support request
2. Reach out to your local Siemens Sales/Support contact
3. Reach out to your regional Siemens Distributor and asking for their oldest applications engineer - the person _most_ likely to __remember__ S5 PLCs (as opposed to someone being forced to support them after becoming a Siemens App. Engr.).
4. Try to export anything that might make recreating screens easier, like tags, graphics/images, icons, fonts (if you want things to look and feel similar)

Please post back the better WinCC option, and how well your migration went, with details that may help others in the future communicating with an S5 PLC using TIA Portal and WinCC [Unified | Professional / Comfort-Advanced].

I look forward to reading your future posts on your migration software selection, and the lessons learned along the way.

BABYCAN

Dear Experts,

I will do an interface migration from Lauer PCS900 to recent HMI unified basic under Tia Portal V19.

It's communicating with an S5 PLC (CPU943B). I will install a module to emulate an ethernet S7-300 PN port.

I have the manual for the Lauer. The structure of application seem very different from Siemens interface.

I would like to limit the modifications to the Step5 PLC program to a minimum.

Do you have hints and suggestions?

Best Regards