XTB-232 X10 RS232 Powerline Interface


JV Digital Engineering


DRAFT  06-28-12 converted from booklet format


The XTB-232 is a high-power RS232 serial powerline interface for X10 automation systems.  It emulates the CM11A "real-time" protocol, and can be directly used as a CM11A substitute for PC-based automation systems such as HomeSeer, Home Control Assistant, or XTension on the Mac.

XTB-232_assembly_v.jpg           XTB-232_active.jpg

Many of you are familiar with the XTB and XTB-IIR X10 Transmit Boosters that have been available since 2006.  The XTB-IIR provides support for the original proprietary X10 TW523 protocol, which was defined before computers became a household item.  The CM11A included a RS232 serial interface to directly interface with computers.  The CM11A has long been out of production, and the XTB-232 was developed as an alternate to provide a more reliable serial powerline interface for PC-based automation systems.

The XTB-232 does not have an internal schedule clock, and will not support any controller functions itself.  It will act as a powerline interface for ActiveHome or ActiveHome Pro running on the PC.  It handles all CM11A direct-action commands, but will not accept any downloaded functions such as timed events or macros.

Like the other XTB units, the XTB-232 outputs a much stronger signal than other X10 transmitters.  While not quite as powerful as the XTB-IIR, it can still output over 20Vpp onto the powerline.  When combined with a good tuned-circuit passive coupler like the XPCP, the XTB-232 located near the distribution panel can provide adequate signals throughout an average home.

Collisions can lock up the real CM11A.  The XTB-232 contains a "polite" transmitter, and will delay its transmission as long as necessary while waiting for a clear line if there is already X10 activity on the powerline.  It will also immediately abort a transmission if it senses a collision, and will automatically retransmit that command after the powerline has cleared.  The handshaking defined in the CM11A protocol document ensures the controlling software knows what is actually happening on the powerline.  Since an acknowledgement is issued over the serial port when a transmission is successfully completed, the automation software can reissue that command when an acknowledgement is not received in a timely manner.

The XTB-232 handles all normal and extended commands, including the pre-set dim commands used to set brightness levels in Insteon dimmers running in the X10 compatibility mode.  The LED indicator provides feedback on the state of the unit.  It should glow dim green whenever it is active and monitoring the powerline.  A bright green flash indicates it is receiving a potential X10 command, and an orange flash indicates it is transmitting.  Red flashes indicate various errors, as explained in detail in the section on LED Status Indications.



The XTB-232 can be plugged into any standard 120V 60Hz AC receptacle.  The closer that receptacle is to the distribution panel, the stronger signals will be throughout the home.  A good tuned-circuit passive coupler like the XPCP should be installed near the electrical panel to propagate the strong X10 signal to the opposite phase when X10 devices are on both phases.  An active coupler/repeater like the XPCR will not do that.


The XTB-232 has an opto-isolated RS232 interface provided with isolated power, so there is complete electrical isolation between the powerline and the computer serial link.  The XTB-232 can be connected to the computer with the same cable that was previously used for the CM11A.  The serial configuration is 4800 baud, 8 bits, no parity, and one stop bit.




The XTB-232 should be identified as the CM11A in the automation software setup configuration.  The software  should recognize the XTB-232 as a CM11A with firmware version 0.  The XTB-232 should then process any X10 communication between the PC and the powerline.


To be compatible with various software programs, the XTB-232 will request clock initialization when first powered up even though it does not have an internal schedule clock.  It will respond to the clock initialization and status request commands, but will just return null bytes for data


The X10 transmitter in the XTB-232 auto tunes itself to 120KHz using the powerline as a reference.  This may be a something to consider when using the XTB-232 in an installation powered by a generator.

To conserve energy, the XTB232 only transmits the X10 signal burst following each 60Hz zero crossing.  Because of this, it is intended for use in homes with a standard 120V/240V split-phase electrical system.  It must be paired with a 3-phase repeater when used in a 3-phase electrical system.

A serial message defined in the CM11A protocol document must be completed within 1 second.  To quickly recover from a serial transmission error, an incomplete serial message will be purged if not completed within one second, and the LED will indicate a serial transmission error.

While the timeout is necessary for robust serial communication, it can make it difficult to send commands manually for testing.  Placing a jumper between pins 4 and 5 of the internal programming header can disable the timeout for manual testing.  Those are the two pins at the end closest to the power transformer.  The timeout should not be disabled for normal operation because it can leave the XTB-232 in an undefined state if the serial communication is interrupted.

The XTB-232 supports the functions detailed in sections 1-4 and 6 of the CM11A Rev 3 Protocol document that can be downloaded here:




Dim green:             The unit is powered up and monitoring the powerline.

Bright green:         A command is being received.

Orange flicker:      A command is being transmitted.

3 red flashes:         A receiving error occurred due to noise or a weak signal.

4 red flashes:         A transmission error occurred due to noise or a collision.

5 red flashes:         An error occurred in the RS232 serial communication link.


For more information, please go to the XTB Home Page.

Please contact me if you have any questions at: jeff@jvde.us
If you don't receive a response within 24 hours, try: xtbjeff@gmail.com