In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Electronegativity wrote:

Hi all, thanks for the input.

John: Your calculation would be correct if the SX could source one amp per pin.

According to the documentation, the SX20 can source 30 milliamps per pin with an absolute maximum value of 45 milliamps per pin.

I read the entire document ( http://www.parallax.com/dl/docs/prod/datast/SX2028AC.pdf ) without seeing an explicit reference to a maximum total current sourced by all pins, but there is something in there that says the power dissapation is 700 milliamps. If this is the correct value then there is no need to worry since running all 12 output pins at their absolute maximum rating would only source 540 milliamps. At the normal output level the sum would be 360 milliamps.

Someone please correct me if the above calculation is wrong!

Paul: I am confused by your diagram; do you have one pin connected to both ground (through the switch) and Vdd?
It looks like throwing the switch would create a short circuit directly from Vdd to ground through the 10K resistor.
is there anything wrong with setting the pin as an output, pulling it high internally, then connecting it to ground through a resistor and a switch so the read command would give 1 if the switch is open and 0 if it is closed?


Would an output pin burn out if I pulled it high internally and then hooked it directly to ground with no resistor?
In order to use John's calculation I would have to know the maximum current that would actually come out of a pin if you pulled it high and connected it directly to ground.

Also, do I need to connect both Vdd pins of an SX20 to +5V and both Vss pins to ground?

I don't mean to be annoying with all the questions, but I burned out half the segments on 3 LED displays over the weekend and would like to avoid a similar fate for the next batch.

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