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TI 305 Controller / DL305 MCS/MCR

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  • TI 305 Controller / DL305 MCS/MCR

    I have an old program listing (1990 printout) from a Texas Instruments 305 Controller. They used the MCS / MCR program control instructions. I've looked at pages 11-50 and 11-51 in the DL305 user manual. My question has to do with the status of the outputs when the MCS/MCR are disabled. If an MCS is enabled and an output is on in the sub power rail, then the MCS becomes disabled. Does the output on the sub power rail remain on or does it switch off with the MCS? I am assuming since the power rail is disabled the output would switch off. I also assume any latching done in the sub power rail would also switch off when the MSC is disabled?

    Thanks!


  • #2
    " I also assume any latching done in the sub power rail would also switch off when the MSC is disabled?"

    While I don't know for certain how it actually works, I would assume that latching (SET/RST)* would NOT switch off. As electronic relay ladder logic was meant to emulate (more or less, more in 1990, perhaps less these days) plain old electromechanical relay logic, and mechanical (set/reset) latching relays are specifically meant to maintain state when power is removed, I'd expect the same to be the case in a disabled MCR rung. By the same reasoning a conventional coil should turn off if anything (including, of course a disabled MCR) interrupts power.

    *At first I assumed that by "latching" you meant SET/RST but on reflection I realize that may not necessarily be the case If by "latching" you mean conventional coil kept on by one its own contacts, then it should turn of if power is interrupted.

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    • #3
      It is a power rail and behaves pretty much like a hardwired rail. If power is removed by an open contact then everything attached to that rail turns off unless you used a SET instruction.
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      • #4
        Thanks! I should have been clear. They are not using the SET instruction. Only latching through the contact of the output.
        I think I've got it now.

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