Pin Instability Feedback with DEBUG Unplugged
Sunflower
Posts: 48
Pin Instability Feedback with DEBUG Unplugged
I have a mystery. I have checked voltages, amps and everything seems normal; stable supply volts (5 V.), output pins (5 V.), parasitic power (<30 ma.), etc. But with a DEBUG statement and a serial cable unplugged at the computer end the output pins destabilize and vary 0.2 to 4.1 volts, and the program seems to freeze at the DEBUG. (Supply volts remain stable.) When I remove the DEBUG statement all pins return to normal. Also, (this ghost haunts me) if I remove the unplugged serial cable from the Motor Mind C board all return to normal. The cable has been checked as straight through. A new cable did the same thing. I am also driving DS1307 clock, 24LC32A EEPROM, PCF8591 ADC, PCF8574 Input Expander, SN754410 H-Bridge, all total about 25 ma. When the instability happens with DEBUG and the unplugged cable then the power used by these chips drop to 19 ma. Isolating these chips had no effect on pin instability. The power source is a 12 V. car battery. The obvious solution would be to remove the cable or remove the DEBUG statements. But it is strange. What is going on here?
I have a mystery. I have checked voltages, amps and everything seems normal; stable supply volts (5 V.), output pins (5 V.), parasitic power (<30 ma.), etc. But with a DEBUG statement and a serial cable unplugged at the computer end the output pins destabilize and vary 0.2 to 4.1 volts, and the program seems to freeze at the DEBUG. (Supply volts remain stable.) When I remove the DEBUG statement all pins return to normal. Also, (this ghost haunts me) if I remove the unplugged serial cable from the Motor Mind C board all return to normal. The cable has been checked as straight through. A new cable did the same thing. I am also driving DS1307 clock, 24LC32A EEPROM, PCF8591 ADC, PCF8574 Input Expander, SN754410 H-Bridge, all total about 25 ma. When the instability happens with DEBUG and the unplugged cable then the power used by these chips drop to 19 ma. Isolating these chips had no effect on pin instability. The power source is a 12 V. car battery. The obvious solution would be to remove the cable or remove the DEBUG statements. But it is strange. What is going on here?
Comments
··········· If you are using the motor mind C carrier board then you will not have the two .1uf· caps on the ATN line this could be causing the serial cable to act like and antenna and reset the stamp though the ATN line when the serial cable is disconnected from the PC.
I’m not sure about the debug, unless it is getting noise on to the ATN line from the TX of the PC.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Stephen Swanson
Technical Support
Parallax, Inc.
sswanson@parallax.com