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Yep, there is enough I/O on the 400 and I believe anything but the smallest 400 has enough memory for the program. As for cycle time, yes, that was what I was meaning. I believe anything above the 414 series should actually be fast enough for my needs, it would just be good to find this out for definite.

Hi, I'm upgrading from an Allen Bradley PLC-5/40 to a Siemens S7-400. I've been trying to find out cycle times for each but to no avail - all I can find is the I/O scan time for the AB and the bit operation times for the S7. Would anyone know roughly what a comparable S7 version would be, performance and speed wise, to the PLC-5/40? Thankyou. Stevo

Well, I think I've finally worked out what I'll need for this - 3 networked S7-226s with appropriate expansion cards. However I'm not entirely sure how to network them - should I use an Ethernet connection, or use the MPI/PPI connection? Would I be right in assuming that I would have one Master and 2 slaves - the master would use NETR to get the status of the inputs from the slaves and save this to memory on the master itself. Also a similar process for the outputs I would assume. I can foresee a potential problem with this - the program already uses a fair amount of flags, so I don't know whether or not I would actually manage to store all this data on the one PLC. Also, the Allen Bradley uses some make of viewing terminal (HMI), will i need to get a new siemens version of this to make it work with the new program and PLC? I cant actually atm remember what make it is. I'm just really needing to know whether or not I am on the right sort of track, though any help you can give me will be greatly appreciated!

Thanks, although that really wasnt the answer I was wanting to hear, it was the one I expected. I'm currently reading the pdf mentioned on this forum - its actually the most informative read I've found so far. Has cleared up some confusion I had. One other thing - the PLC-5 has something like 340 inputs and 190 outputs on it. I dont know whether or not there is more than just the PLC (I think one can have up to 1K inputs?) as I haven't actually had a chance to see the thing yet. Atm, all I have seen is the program listing, which at almost 1000 pages is rather large. What I'm wondering is the fact that the S7-226 can have 128/120/248 - inputs/outputs/max channels over 7 expansion cards. Does this mean the total inputs can only be 128, with 120 outputs, or can you have a total of 248 inputs and 0 outputs? Either way I believe I will need to network 2 or more S7's together. I have read up on the hardware aspect of this, but I can't seem to find any information on the programming side. Does having the S7's networked mean changing the program in any specific way? ie. how do you go about accessing an input on a different PLC? Fair amount of questions there! I cant seem to find the answers on the net or the books I have here so hopefully some of you will be able to help!