Terry, (and others interested in process simulation) We had trouble with commenting the CALC blocks back in 1988 while working on our first IA project initial installation. We learned that there was some magic to how many characters the calc block would process on each line before considering the rest to be a comment. Later the ; semicolon was used as a comment separator. Since that time we have implemented our logic as Joseph Wu suggested on the list so your operation would look like this: CST IN BI01 IN BI02 IN BI03 IN BI04 OR 4 OUT BO01 END =09 Yes, this method uses more steps and that might have been the reason someone tried to condense the logic. As an aside, I never feel comfortable enough to just write sequence code or calc blocks and install them without testing them. I used to do this by dummying the inputs before connecting them to the final parameters. For instance, to test your logic I would have written the steps, and before connecting anything to BI01 through BI04, I would have typed a "1" into BI01 with zeros in BI02 through BI04, and watched BO01 transition to TRUE on the block detail display and then worked my way through BI02 through BI04 in like fashion. I've gotten used to doing this because there are a lot of opportunities to make a typo in the STEP logic such as having two BI01's and no BI02 or other brain farts that would compile but wouldn't work as I intended. =20 Before we started using Esscor's FSIM CP Emulator coupled with their SIM4ME simulator package I used to do the same thing to test sequence logic. This gave me the best comfort factor that my code not only compiled, but functioned exactly like I wanted it to. (ESSCOR sales pitch follows): =20 (Janet Parker, please send my commission checks to my home address ;<) IN ESSCOR's FSIM "CP" we are able to leave all of the block connections intact and then use SIM4ME to dummy the signal all the way through the FBM's ECB's just as if the field I/O point had transitioned from an open contact to a closed one. In addition, by creating simulation logic based on DCS outputs we can drive the associated inputs to create the same feedback that the live process would normally provide. =20 For discrete loops, if we open a block valve that has an open and closed limit switch we can make the CIN points transition to their expected state. For PIDA controllers we can use the output value it drives through an AOUT point in a SIM4ME calculation that will dynamically change the AIN point as an appropriate feedback for the PIDA.MEAS. In previous simulations we created, or used, we had to change .IOMOPT of IO blocks to zero instead of 1 to accomplish the simulation and then had to make sure that we changed them back before copying the compound to the live system. With ESSCOR's offering the Control application software, (Foxboro's Compounds), remain untouched and run in the FSIM CP. The loopback simulation applications you create using SIM4ME can be built and saved as a separate entity. Setting this all up the first time is not for the faint of heart and we continue to have some technical difficulties keeping it all running at times, but ESSCOR has provided good service and we have made a step change in the way we provide new control applications to our production department. Production uses our simulations for operator training while we use it to test and verify that our control logic is free of typos and or bad connections before we transport it, unchanged, to the live system by using the same ICC driver tasks used by any other Foxboro CP. Since the FSIM CP is just another station on the Foxboro nodebus, you can even establish peer-to-peer connections with other CP's/WP's/Historians, or in our case a TRICONEX TRICON that also communicates on the nodebus via a FoxGuard module. The TRICON, (SIS applications), can then work in conjunction with the Foxboro controllers or ESSCOR's FSIM CP to provide a complete emulation of your process control and SIS systems. =20 This approach requires a certain economy of scale to make it an economically feasible solution, but for large scale operations it is the "Cat's Meow" Cheers, Tom VandeWater Control Systems Developer/Analyst Dow Corning Corporation Carrollton, KY USA _______________________________________________________________________ This mailing list is neither sponsored nor endorsed by Invensys Process Systems (formerly The Foxboro Company). Use the info you obtain here at your own risks. Read http://www.thecassandraproject.org/disclaimer.html foxboro mailing list: //www.freelists.org/list/foxboro to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join to unsubscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave