Hello,
I designed an I/O card which has 12 digital inputs and 8 digital outputs and 3 status leds. For digital outputs, I have another 8 leds that show digital output status (For example, if digital output 1 is ON, digital output status led 1 is ON).
Digital outputs will drive 24V relays. And inputs are 24V digital inputs. I use RS485 line(isolated using ISO3088) to set and reset the digital outputs and I send characters to set and reset the outputs using Putty. Microcontroller echoes back the received character.
I want to share some part of my circuit.
Here is the processor:
Status leds:
Digital outputs:
And the last one digital output status leds:
The strange behaviour occurs following situations:
1) If I use 820R for leds (like launchpads) and test the card at full performance (all leds are ON, all digital outputs are ON and status leds are ON), MSP430 begins to confuse at 4th digital output setting (Echoed characters mixture on console) and P7.7 and P7.6 shorted! The relay connected to P7.7 (first output) begins to set and reset rapidly.
2) I increased digital output resistors and status resistors to 4k7Ohm connected to the MSP430F5529. All digital output setting test is OK, but some time later P7.7 and P7.6 are shorted again. I measured Ohm value between P7.7 and P7.6 and it is 40Ohms.
It is too weird that touching by soldering iron to P7.7 and P7.6 fixes the short circuit problem for some time.
How can I solve this problem. Thank you!
