I have two issues to solve:

I made a JDM programmer which works fine, but its voltages are somewhat beyond the values permitted for the 16F877A, namely, low DATA and CLOCK are about -0.6 V when the processor is connected (-1 V without processor), and about 5.8 V for HIGH, with the supply voltage around 5.2 V. Programming Voltage is around 13.5 V. In the data sheet a maximum of -0.3 V and +0.3 V above VDD is permitted.

Question: is this normal for JDM? Could it affect the reliability of the processors? I am not getting any errors, but the idea is to use these processors as loggers which should work for several months unattended.


In the data sheet for 16F877A for 4 MHZ 5V a current of 1.5 mA is given. I am getting a reading of about 6 mA (processor doing a Loop, with everything off). The circuit I am using is a very simple one, a digital thermometer chip DS1820 (which has a standby current of 1 uA), crystal, and two indicator LEDs. Since the device is intended to work for about 3 months on rechargeable batteries, the difference between 1.5 and 6 is huge. Can someone give a hint as to what can be done to reduce the power consumption. I have tried two different processors and it is the same story.

I have left the unused pins of the 16F877 floating and by default as inputs, RB internal pull-up resistors are disconnected. I assume that floating inputs would not affect the power consumption?

 

remove the led's. they typically require from a few to 20 ma each. do not float inputs it can actually destroy the chip and could use current.

 

Thanks for the tips. The LEDs are obviously turned off. I assume that setting TRIS as output does not increase consumption if the pins are set to LOW.

 

Not sure if high or low uses current, but outputs are ok to float, and you should, I think.

 

Thanks again,

I have set all unused pins to output LOW, and got 1.2 mA consumption at 5.5 V, down from 5 mA!