X10 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.
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X10 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 PSC05 provides 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 PSC05 be within 50 µs of this 60 Hz zero crossing
reference square wave.
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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 PSC05 modulates its
input (from the O.E.M.) with 120 kHz, therefore only the 1 ms "envelope" need be applied
to its input. 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.
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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.
See Figure 2.
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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).
See Figure 3.
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.
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[1] Hail Request is transmitted to see if there are any X10
transmitters within listening range. This allows the O.E.M. to assign a different Housecode if a
"Hail Acknowledge" 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 X10 modules causing erroneous operation.
Extended Code is similar to Extended Data: 8 Bit bytes which follow
Extended Code (with no gaps) can represent additional codes. This allows the designer to
expand beyond the 256 codes presently available.
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NOTE 1
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X10 Receiver Modules require a "silence" of 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 PSC05 Two-Way Power Line Interface cannot receive Extended Code or Extended
Data because these codes have no gaps between them. The PSC05 can only receive standard
"pairs" of 11 bit X10 codes with 3 power line cycle gaps between each pair.
NOTE 3.
The PSC05 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 PSC05
will not be a continuous stream of dim and bright codes like the codes which are transmitted.
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A Square wave representing zero crossing detect is provided by the
PSC05 and is within 100 &s of the zero crossing point of the AC power line. The output signal
envelope from the O.E.M. should be within 50 &s of this zero crossing detect. The signal envelope
should be 1 ms (-50µs +100µs). See Figure 5.
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Opto-Coupled 60 Hz reference output (from the
PSC05)
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 PSC05 is designed to
be interfaced to other microprocessor circuitry which outputs X10 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
"isolated" power supply. It is necessary to maintain this isolation, therefore the
trigger circuit normally used in X10 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
PSC05. X10 codes generated by the O.E.M. product are to be synchronized to this zero
crossing reference. The X10 code envelope generated by the O.E.M. is applied to the PSC05
which modulates the envelope with 120 kHz and capacitively couples it to the AC power line.
Opto-Coupled Signal Input (to the PSC05)
The input signal required from the O.E.M. product is the signal
"envelope" of the X10 code format, i.e.
High
for 1 ms. coincident with zero crossing represents a binary "1" 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 "0"
and turns the 120 kHz oscillator/output circuit off for the duration of the 1 ms. input.
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Opto-Coupled Signal Output (from the
PSC05)
The "X10 received" output from the PSC05 coincides with the
second half of each X10 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 PSC05. See Figures 6, 7, and 8.
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Source: X10 WorldWideWeb pages
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