X10 Community Forum

💬General Category => General Discussion => Topic started by: macrobob on January 19, 2011, 05:15:20 PM

Title: CM17A RTS DTR voltage levels
Post by: macrobob on January 19, 2011, 05:15:20 PM: Does anyone know what the CM17A voltage level requirements are? Does it use +/- for one and zero or just 0+?

Thanks,
Bob
Title: Re: CM17A RTS DTR voltage levels
Post by: Dan Lawrence on January 19, 2011, 05:29:35 PM: Check this: FireCracker™Computer Interface

No bigger than a Fig Newton (but a lot lighter and power-packed), the interface plugs into a serial port in the back of your computer. Our through-port design allows you to plug another device into the back of the interface -- you need not lose a serial port to use FireCracker!

Info is at www.x10.com/automation/ck18a_s_ps32.html
Title: Re: CM17A RTS DTR voltage levels
Post by: macrobob on January 19, 2011, 05:44:21 PM: 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.
Title: Re: CM17A RTS DTR voltage levels
Post by: pconroy on January 19, 2011, 06:07:17 PM: Quote from: macrobob on January 19, 2011, 05:44:21 PM
I know all that, I am not using it on a standard computer

are you using a USB/RS232 adapter?
Title: Re: CM17A RTS DTR voltage levels
Post by: -Bill- (of wgjohns.com) on January 20, 2011, 03:44:01 AM: Quote from: macrobob on January 19, 2011, 05:44:21 PM
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.
>!
Title: Re: CM17A RTS DTR voltage levels
Post by: Brian H on January 20, 2011, 06:08:09 AM: 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.