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[macrobob]

Does anyone know what the CM17A voltage level requirements are? Does it use +/- for one and zero or just 0+?

Thanks,
Bob

[Dan Lawrence]

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[macrobob]

I know all that, I am not using it on a standard computer. I know the CM17A protocol and just need to know if it wants to see CTS go negative for a one or go to zero. Rs-232 is inverted.

[pconroy]

I know all that, I am not using it on a standard computer

are you using a USB/RS232 adapter?

[-Bill- (of wgjohns.com)]

I know all that, I am not using it on a standard computer. I know the CM17A protocol and just need to know if it wants to see CTS go negative for a one or go to zero. Rs-232 is inverted.

As signal levels go for the RS232 specification, ground is generally not a "signal".  So, it must go either positive or negative.

Assuming X10 may have taken a shortcut, grounding the pin is less likely to be damaging than going negative is, so you may want to try that first, but I would expect the line to switch positive or negative and not positive or ground.
 

[Brian H]

I looked at the CM17A schematic and the PIC12C508 datasheet.
As Bill suspected. X10 used some shortcuts. Like counting on the protective diodes in the IC to limit the + and - voltages on the input pins through a 100K resistor..

Since I found no official data from X10 this is an educated guess.
If X10 chose to enable the weak pullup resistors {~20K with a VDD +5 volts} for the GP0 and GP1 inputs. A 0 voltage on the RTS and DTR pins through the series 100K resistor, will not be a low enough on the GP0 and GP1 pins of the IC. If the pullups are not enabled. Then the 0 volts should work.