Posted 31 Jan 2015 My project is converting a Quatum Modicon to a Control Logix. We took the Modicon Logic ran it thru a Rockwell converter and created the Control Logix Logic. This was nothing complicated but a large file. In Modicon you have a Memory retentive bit -- (M). This converted to a Latch (OTL) in the Control Logix, we decided to place a coil OTE in Parallel with the Latch so we could unlatch on the rung going false. The memory retentive coil is there to hold memory on power cycle if it ever happened. So.... The question is Unlatch below The latch, or above Consider left a representive of converted logic in the AB. Logic a bit more complicated. A B C lL. U --||--|||--|/|--(OTL)--(OTE). L |. . --||-----|. U. L ----||--------------------(OTU) Share this post Link to post Share on other sites
Posted 31 Jan 2015 (edited) I don't know if that will work. If you want your OTL bits to remain on after a power cycle, I don't think you're allowed to have an OTE assigned to it. I'm pretty sure that will nullify any "latching" properties over a power cycle. Here's a really good thread about the subject. I linked directly to a post made by Ron Beaufort, it covers the topic thoroughly. If you have a bit that needs to remain true over a power cycle, you'll probably have to modify the logic to use OTL and OTU instructions exclusively. Edit: Reading Ron's post a little more, you can use this trick to force an OTE to be retentive (read the rung comments for explanation, or read the full info in his post): Edited 31 Jan 2015 by MrAutomation Share this post Link to post Share on other sites
Posted 31 Jan 2015 You don't need to retain the state of a coil with an M-bit (a Modicon feature) in ControlLogix. Just simply use the OTL and OTU and the bit state will be memorized during a power-off condition. I'm sure you are aware its generally frowned to use latches with direct outputs, best to use an internal coil and have the output follow its state in a rung. Share this post Link to post Share on other sites