Connecting Multiple PLC types

Does anyone have any suggestions on connection a SLC 504, Siemens S7 and a micrologix 1500 together so they can all talk to each other?

You will probably need some kind of serial communications bridge. I'd contact Prosoft (http://www.prolinxgateways.com/) or Phoenix Digital (http://www.phoenixdigitalcorp.com/) - they specialize in pulling this kind of rabbit out of their hat!

You're always going to have some kind of tradeoff between speed and complexity and cost.

My approach would be to use the S7 as a Profibus DP master, then to use a Profibus DP/DF1 protocol interface box at both A-B controllers (because both support DF1 Half Duplex).

http://www.prolinxgateways.com/products/4105.html

The absolute cheapest way to get ProfibusDP/Serial interfaces would be to use ASCII instructions at the SLC and MicroLogix and use ProfibusDP/ASCII converters.

http://www.mksinst.com/cgi-bin/product.exe?pid=PFB366

If Hilscher had their Profibus DP interface for the A-B Compact platform out already (not until March 04) you could use in-chassis Profibus DP adapters at the SLC-5/04 (from SST) and MicroLogix 1500 (from Hilscher) and have very fast data exchange.

A pretty nice solution for this would be a Factory Gateway from Pro-Face. Available through Xycom in the U.S

http://www.pro-face.com/product/fgw.htm

You would need 3 factory gateways, one for each PLC serial port and Ethernet would tie the FGs together. Using their software, Pro-Server you would configure the data you want to exchange between the PLCs. It is a pretty simple configuration. The FGs list for $595 each and the Pro-Server lists for $795.