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About Nikolay

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  1. AB Micrologix atomic memory read

    I found solution that satisfies my needs. I had to ask the original question because I thought that it will require two separate bitwise instructions to copy a 32-bit integer from an "L" file to two words in a "N" file. I discovered the CPW (Copy Word) instruction, which copies blocks of data from one location to another. Since this is done in a single step, this solves my problem.
  2. AB Micrologix atomic memory read

    Yes, and this is how I arrived to this question. The library I am using can't read 32 bit "L" files, but it can read N files. So, my idea is to store 32 bit integers as two 16-bit words in an N file. Then read N file and assemble 32-bit integers using bitwise operations. And I do not want to end up in a situation when a 32 bit integer stored as N20:0 and N20:1 arrives corrupted because word N20:1 was updated while the program was reading the table.
  3. I am reading memory from Micrologix 1400 PLC with an external library. The documentation for the library says: For example, let's say my program reads memory location N20 which consists of 4 words. Before the read operation begins, all words in N20 are set to "0". While read operation is in progress, the PLC writes value "10" to memory location N20:3. Based on the data from manual (that it uses SLC 5/00 Protected Typed Reads), what will be the result of read operation? Will it include the value "10" that was written by PLC in the middle of read operation or it will be "0" as it was when the read operation begun? In other words, are "SLC 5/00 Protected Typed Reads and Writes" atomic operations on PLC Micrologix 1400?
  4. The card has stopped working today. So, what I described in the first post is an indicator of the card dying.
  5. Good day, I have Allen Bradley Compact Logix PLC with few I/O cards, there are 5 analog output cards amongst them. Today one of the analog cards does not provide more then 3.8 Volt on the outputs. Any voltage between 0 and 3.8 V is supplied correctly, whereas anything above it results in 3.8 V only. The card does not report any errors to PLC. Other cards do not have this problem. The PLC was running non-stop for couple of years and yesterday it was turned off for an hour. The problem started right after this. I have checked the module settings and verified that the output is not limited to 3.8V Can anyone give any advice in regards to this situation?
  6. Dear Community, I have the Allen-Bradley 1769-L32E Compact Logix 5332E PLC and a C-more touchscreen. Assume that there is a pushbutton at the touchscreen (set up as momentary) that sets a bit at particular PLC address (call it hmi_button_1) On the PLC this bit is checked twice within one routine - on two rungs that are directly adjacent to each other.     So, my question is: Is it possible that the state of hmi_button_1 will be different within one routine  execution cycle? For example rung 1 reads it as FALSE while rung 2 reads it as TRUE (or vise versa)? Or state of bits is guaranteed to be the same for one complete routine execution cycle?   Best, Nikolay.