IBM Aptiva S9H 250-0463 X-10 Technology Transmission Theory

Aptiva C66
(250-0458)   X-10 Technology Transmission Theory      Faxback Doc. # 34389

X-10 communicates between transmitters and receivers by sending and
receiving signals over the power line wiring.  These signals involve short
RF bursts which represent digital information.

Transmission Theory

X-10 transmissions are synchronized to the zero crossing point of the AC
power line.  The goal should be to transmit as close to the zero crossing
point as possible, but certainly within 200 microseconds of the zero
crossing point.  The PL513 and TW523 provide a 60 Hz square wave with a
maximum delay of 100 µsec from the zero crossing point of the AC power
line.  The maximum delay between signal envelope input and 120 kHz output
bursts is 50 µsec.  Therefore, it should be arranged that outputs to
the PL513 and TW523 be within 50 µs of this 60 Hz zero crossing
reference square wave.

A Binary 1 is represented by a 1 millisecond burst of 120 kHz at the zero
crossing point, and a Binary 0 by the absence of 120 kHz.  The PL513 and
TW523 modulate their inputs (from the O.E.M.) with 120 kHz, therefore only
the 1 ms envelope need be applied to their inputs.  These 1 millisecond
bursts should equally be transmitted three times to coincide with the zero
crossing point of all three phases in a three phase distribution system.
Figure 1 shows the timing relationship of these bursts relative to zero
crossing.

A complete code transmission encompasses eleven cycles of the power line.
The first two cycles represent a Start Code.  The next four cycles
represent the House Code and the last five cycles represent either the
Number Code (1 thru 16) or a Function Code (On, Off, etc.).  This complete
block, (Start Code, House Code, Key Code) should always be transmitted in
groups of 2 with 3 power line cycles between each group of 2 codes.  Bright
and dim are exceptions to this rule and should be transmitted continuously
(at least twice) with no gaps between codes.

Within each block of data, each four or five bit code should be transmitted
in true compliment form on alternate half cycles of the power line.  I.E.
if a 1 millisecond burst of signal is transmitted on one half cycle (binary
1) then no signal should be transmitted on the next cycle, (binary 0).

The Tables in Figure 4 show the binary codes to be transmitted for each
House Code and Key Code.  The Start Code is always 1110 which is a unique
code and is the only code which does not follow the true complimentary
relationship on alternate half cycles.

 [1] Hail Request is transmitted to see if there are any X-10 transmitters
within listening range.  This allows the O.E.M. to assign a different
Housecode is received.

[2] In a Pre-Set Dim instruction, the D8 bit represents the Most
Significant Bit of the level and H1, H2, H4 and H8 bits represent the Least
Significant Bits.

[3] The Extended Data code is followed by 8 bit bytes which can represent
Analog Data (after A to D conversion).  There should be no gaps between the
Extended Data code and the actual data, and no gaps between data bytes.
The first 8 bit byte can be used to say how many bytes of data will follow.
If gaps are left between data bytes, these codes could be received by X-10
modules causing erroneous operation.

Extended Code is similar to Extended Data: 8 Bit bytes which follow
Extended Code can represent additional codes.  This allows the designer to
expand beyond the 256 codes presently available.

IMPORTANT NOTES

NOTE 1. X-10 Receiver Modules require at least 3 power cycles between each
pair of 11 bit code transmissions (no gaps between each pair).  The one
exception to this rule is bright and dim codes.  These are transmitted
continuously with no gaps between each 11 bit dim code or 11 bit bright
code.  A 3 cycle gap is necessary between different codes, i.e. between
bright and dim, or 1 and dim, or on and bright, etc.

NOTE 2.  The TW523 Two-Way Power Line Interface cannot receive Extended
Code or Extended Data because these codes have no gaps between them.  The
TW523 can only receive standard "pairs" of 11 bit X-10 codes with
3 power line cycle gaps between each pair.

NOTE 3.  The TW523 can receive dim and bright codes but the output will
represent the first dim or bright code received, followed by every third
code received.  i.e. the output from the TW523 will not be a continuous
stream of dim and bright codes like the codes which are transmitted.

Transmission Timing Diagrams

A Square wave representing zero crossing detect is provided by the
PL513/TW523 and is within 100 µs of the zero crossing point of the AC
power line.  The output signal envelope from the O.E.M. should be within 50
µs of this zero crossing detect.  The signal envelope should be 1 ms.
(-50us +100us) See figure 5.  Note (us stands for microseconds)  

Opto-Coupled 60 Hz reference output ( from Pl513/TW523)

Transmissions are to be synchronized to the zero crossing point of the AC
power line and should be as close to true zero crossing as possible.  The
PL513 and TW523 are designed to be interfaced to other microprocessor
circuitry which outputs X-10 codes synchronized to the zero crossing point
of the AC power line.  It is therefore necessary to provide a zero crossing
reference for the O.E.M. microprocessor.

It is likely that this microprocessor will have its own power supply.  It
is necessary to maintain this isolation, therefore the trigger circuit
normally used in X-10 POWERHOUSE controllers is  not desirable as this
would reference the O.E.M. power supply to the AC power line.  It is also
not desirable to take the trigger from the secondary side of the power
supply transformer as some phase shift is likely to occur.  It is therefore
necessary to provide an opto-coupled 60 Hz reference.

An opto-coupled 60 Hz square wave is provided at the output of the PL513
and TW523.  X-10 codes generated by the O.E.M. product are to be
synchronized to this zero crossing reference.  The X-10 code envelope
generated by the O.E.M. is applied to the PL513 or TW523 which modulates
the envelope with 120 kHz and capacitively couples it to the AC power line.

Opto-Coupled Signal Input 

The input signal required from the O.E.M. product is the signal of the X-10
code format, i.e.

High for 1 ms. coincident with zero crossing represents a binary and gates
the 120 kHz oscillator through to the output drive circuit thus
transmitting 120 kHz onto the AC power line for 1 ms.

Low  for 1 ms. coincident with the zero crossing point represents a binary
and turns the 120 kHz oscillator/output  circuit off for the duration of
the 1 ms. input.

Opto-Coupled Signal Output

The output from the TW523 coincides with the second half of each X-10
transmission.  This output is the envelope of the bursts of 120 kHz
received.  Only the envelope corresponding to the first burst of each group
of 3 bursts is available at the output of the TW523.

(/DD/BKL-08/23/96)