Thank you Alex - good explanation and certainly makes sense. Two other thoughts if and when you have time... Do the order of the Module ECBs and their Child ECBs make any difference? Would Child ECBs (FoxCom, DCIs, etc.) be considered to add the same additional I/O processing as Module ECBs (i.e. count the same in adding up the chain)? We have traditionally installed them in the same (logical?) order as they are physically installed. This makes good readability in the Control Configurator and Fox Select display. Now it looks like it may also serve to help identify and order by length of chain. F20100 - FCM - F20101 - FBM - F20101 - FBM - F20103 - FBM - 0103_1 - Child ECB - 0103_2 - Child ECB F20200 - Next FCM - etc. - Tom Badura Plastics Engineering Company 920-458-2121 x3366 tbadura@xxxxxxxxxx -----Original Message----- From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On Behalf Of Johnson, Alex P (IPS) Sent: Thursday, February 12, 2009 6:52 PM To: foxboro@xxxxxxxxxxxxx Subject: Re: [foxboro] FCP vs. ZCP? (forked from: network storm) Tom, The UCM was an older controller whose I/O can be attached (migrated) to a CP270. As far as FCM loading is concerned, you can improve overall I/O response by using more FCMs per ZCP. You can improve if further by ordering the ECBs for the FCMs properly in the _ECB compound. When the ZCP wants I/O, it sends messages to the FCMs that hold that I/O in the order that their ECBs appear in the _ECB compound. It then calculates how long it should wait for the first FCM to gather its I/O and then asks for it. If the FCM is finished gathering, the ZCP gets the data and moves to the next FCM. If the FCM is busy, the ZCP sits backs and waits a bit more before asking again. This cycle is repeated as necessary. Since the FCMs are queried in parallel, the more of them you have the more parallel processing can be achieved and the less the ZCP has to wait for its data. Also, as you might have realized, this means that FCMs with short FBM chains should be place higher on the list of ECBs in the _ECB compound. This allows the ZCP to wait a shorter time to get that data. Since the other FCMs are processing in parallel, it is increasingly likely that they will be ready if they are listed in increasing chain length. Does this make some sense? _______________________________________________________________________ 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