PE Kit Labs - Threshold Logic Voltage
Steve Nelick
Posts: 25
I'm working on the Propeller Education Kit Labs, the latest lab, named Counter Modules and Circuit Applications. And, I'm on the first exercise in that lab, which is: Measuring RC With Positive Detector Mode.
On page 3 of the lab,·in a section·titled Measuring RC Decay, it says the Propeller threshold voltage is 1.65 volts. So, what I expected was the Propeller Counter Module would count while the Propeller pin was HIGH, above 1.65, and stop counting when the pin was LOW, below 1.65 V.
When·I look at the RC decay on·an OPTAscope it looks like the Propeller Counter Module stops counting·when the RC·decay·drops below 1.35 volts, not 1.65 volts. So, my question is: what happened to the 1.65 volt threshold?
I tried to measure the Propeller threshold voltage by·using·a 4.7 K resistor in series with a 10 K pot. The results I got were: the Propeller reported HIGH from 3.3 v down to 1.46 v, and LOW from 0.0 V up to 1.36 v. Between 1.36 v and 1.46 v, the Propeller·sometimes reportd·HIGH and sometimes LOW. I searched the Propeller Forum, and I found a note from Ariba that said he measured the Propeller threshold voltage·at 1.41, which is consistent with what I measured.
I looked at the Propeller Data Sheet, and it says the Propeller threshold is 1/2 VDD or 1.6 @ 3.3 VDC. I measured VDD, at a pin on the Propeller label identified as 3.3V, and the reading was 3.3 v, which I guess is VDD.
On page 3 of the lab,·in a section·titled Measuring RC Decay, it says the Propeller threshold voltage is 1.65 volts. So, what I expected was the Propeller Counter Module would count while the Propeller pin was HIGH, above 1.65, and stop counting when the pin was LOW, below 1.65 V.
When·I look at the RC decay on·an OPTAscope it looks like the Propeller Counter Module stops counting·when the RC·decay·drops below 1.35 volts, not 1.65 volts. So, my question is: what happened to the 1.65 volt threshold?
I tried to measure the Propeller threshold voltage by·using·a 4.7 K resistor in series with a 10 K pot. The results I got were: the Propeller reported HIGH from 3.3 v down to 1.46 v, and LOW from 0.0 V up to 1.36 v. Between 1.36 v and 1.46 v, the Propeller·sometimes reportd·HIGH and sometimes LOW. I searched the Propeller Forum, and I found a note from Ariba that said he measured the Propeller threshold voltage·at 1.41, which is consistent with what I measured.
I looked at the Propeller Data Sheet, and it says the Propeller threshold is 1/2 VDD or 1.6 @ 3.3 VDC. I measured VDD, at a pin on the Propeller label identified as 3.3V, and the reading was 3.3 v, which I guess is VDD.
Comments
Vil, Logic Low ... Vss to 0.3Vdd
Vih, Logic High ... 0.6Vdd to Vdd
That's 0V-0.99V, 1.98V-3.3V respectively at 3.3V
Page 4 does suggest the threshold is 1/2 Vdd.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Paul Baker
Propeller Applications Engineer
Parallax, Inc.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Paul Baker
Propeller Applications Engineer
Parallax, Inc.