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LDmicro Forum - upside-down |
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upside-down (by Arief Wibowo)
1. TON and TOF LDMicro fasility for AVR Microcontroller is upside down (apply active low circuit).
2. Up Counter one varianced will apply active low circuit for AVR Microcontroller. Thank you so much..
(no subject) (by Jonathan Westhues)
The usual reason for this problem is that your AVR board has the inputs and outputs wired active LOW. This will happen if the switches are wired to ground, with pull-up resistors, and the LEDs are wired to Vcc, with the cathode at the output pin. So the input pin will be low when the button is pressed, and the LED will turn on when the output goes low.
This is the opposite of what LDmicro expects. If that's the problem, then AND and OR operations (from series and parallel contacts) will also seem to be reversed. The fix would be to tell the compiler that your inputs and outputs are active low, by marking the coils and contacts as negated.
(no subject) (by IngeJacobo)
Hi Everybody....
Yes, Mr Westhues answer is right, the usual way the pushbuttons switches are wired (in a commercial microcontroller development board) is active LOW, howewer, on a commercial PLC, this is not the way things are, neither for LDmicro. both "see" the iputs as they are WIRED, either as N.O. or N.C. contacts, thats the reason LDmicro (or any other ladder-logic programming sotware) has N.O. and N.C. contacts as programm elements. The usual way the input/output components are shown in a ladder schematic (control schematic of any industrial machine on paper) is in their "normally" (DEACTIVATED) state, but, and this is VERY IMPORTANT, you can programm the INPUTS as N.C. or N.O. elements in the PLC program, regardlees of their real state or condition on the outside world. thats the beauty of PLCs and Ladder Logic Programming. Hope this helps to clear the subject.
(no subject) (by bhavesh)
hi
Arief Wibowo & Arief Wibowo thanking you very much now i understand bhavesh
(no subject) (by bob dole)
had a similer problem before. fixed it without having to change the code. just used the output to power a npn transistor. so the pic output sent a p signal to the npn. the negative powered the device.
just looking back on the project there it was a relay board i had bought on ebay that needed a negative siganl to activate each relay so rather then change my code which was done the other way around i just used npn transistors. hope that helps( i realize your situation might be different though)
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