Standard Transmission

An X-10 transmission from the PC to the interface typically refers to the communication of a House code and Device Code combination or transmission of a function code. The format of these transmissions is:

                                PC                                           Interface

2 bytes                 Header:Code

1 byte                                                                   checksum

1 byte                   Acknowledge

1 byte                                                                   interface ready to receive

This format is typical of all transmissions between the PC and the interface with the difference being in the first transmission from the PC.


The Header:Code combination is configured thus:

                Bit:         7   6   5   4   3   2   1   0

                Header:                < Dim amount    >   1  F/A E/S


Dim amount (dims) is a value between 0 and 22 identifying the number of dims to be transmitted (22 is equivalent to 100%)

Bit 2 is always set to '1' to ensure that the interface is able to maintain synchronization. F/A defines whether the following byte is a function (1) or address (0).


E/S defines whether the following byte is an extended transmission (1) or a standard transmission (0).

                Bit:          7   6   5   4   3   2   1   0

                Address: < Housecode >   <Device Code>

                Function:< Housecode >   < Function  >

Note the function only operates for devices addressed with the same House code. 

Interface Checksum and PC Acknowledge

 Whe n the interface receives a transmission from the PC, it will sum allof the bytes, and then return a byte checksum. If the checksum is correct, the PC should return a value of 0x00 to indicate that the transmission should take place. If however, the checksum is incorrect, then the PC should again attempt to transmit the Header: Code combination and await a new checksum.

Interface Ready to Receive.

 Once the X-10 transmission has taken place (and this may be quite time consuming in the case of Dim or Bright commands) the interface will send 0x55 to the PC to indicate that it is in a 'ready' state.