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TW(4)               FreeBSD Kernel Interfaces Manual (i386)              TW(4)

     tw - TW-523 X-10 device driver

     Tw is the driver for the TW-523 power line interface, for use with X-10
     home control products.  The X-10 protocol is compatible with a number of
     home control systems, including Radio Shack ``Plug 'n Power(tm)'' and
     Stanley ``Lightmaker(tm).''

     The driver supports read() write() and select() system calls.  The driver
     allows multiple processes to read and write simultaneously, but there is
     probably not much sense in having more than one reader or more than one
     writer at a time, and in fact there may currently be a race condition in
     the driver if two processes try to transmit simultaneously (due to
     unsynchronized access to the sc_pkt structure in tw_sc).

     Transmission is done by calling write() to send three byte packets of
     data.  The first byte contains a four bit house code (0=A to 15=P).  The
     second byte contains a five bit unit/key code (0=unit 1 to 15=unit 16,
     16=All Units Off to 31 = Status Request).  The third byte specifies the
     number of times the packet is to be transmitted without any gaps between
     successive transmissions.  Normally this is 2, as per the X-10
     documentation, but sometimes (e.g. for bright and dim codes) it can be
     another value.  Each call to write() can specify an arbitrary number of
     data bytes, but at most one packet will actually be processed in any
     call.  Any incomplete packet is buffered until a subsequent call to
     write() provides data to complete it.  Successive calls to write() leave
     a three-cycle gap between transmissions, per the X-10 documentation.  The
     driver transmits each bit only once per half cycle, not three times as
     the X-10 documentation states, because the TW523 only provides sync on
     each power line zero crossing.  So, the driver will probably not work
     properly if you have three-phase service.  Most residences use a two-wire
     system, for which the driver does work.

     Reception is done using read() The driver produces a series of three
     character packets.  In each packet, the first character consists of
     flags, the second character is a four bit house code (0-15), and the
     third character is a five bit key/function code (0-31).  The flags are
     the following:

     #define TW_RCV_LOCAL    1  /* The packet arrived during a local transmission */
     #define TW_RCV_ERROR    2  /* An invalid/corrupted packet was received */

     The select() system call can be used in the usual way to determine if
     there is data ready for reading.

     xten(1), xtend(8)

     TW-523 documentation from X-10 Inc.

              the TW523 special file

     Eugene W. Stark <>

FreeBSD 11.0-PRERELEASE        October 30, 1993        FreeBSD 11.0-PRERELEASE


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