FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
A LINE COMMUNICATION METHOD
EMERSON ELECTRIC CO.,
a US Company
of 8000 West Florissant Avenue
St. Louis, Missouri 63136
USA
Inventor: JOSHI RAJ AN
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF DISCLOSURE
The present disclosure relates to the field of data communication between a plurality of units.
DEFINITIONS OF TERMS USED IN THE DISCLOSURE
The expression 'unit' used hereinafter in this disclosure refers to but is not limited to an HVAC unit, a furnace, an air-handler, a thermostat, a temperature control unit, a pressure control unit, an electric motor, a compressor, a valve, a regulator, a gearbox, a circulator and the like.
The expression 'controller' used hereinafter in this disclosure refers to but is not limited to microcontrollers, microprocessors, Application Specific Integrated Circuits (ASIC) and Digital Signal Processors (DSP).
These definitions are in addition to those expressed in the art.
BACKGROUND
Sophisticated units for cooling/heating of enclosed spaces such as residential and commercial buildings have been developed for providing greater comfort to occupants of such spaces. Typically, in any unit, control systems are coupled with the unit for controlling the operation of the unit. Control systems generate signals which turn the unit ON/OFF, thereby providing a comfortable temperature regulated environment. Typically, control systems generate these signals in response to signals from feedback systems.

For large residences or commercial installations, where capacity requirements for cooling/heating of an enclosed space are high, instead of using a single large unit, it is preferable to use two or more units together in order to provide sufficient cooling/heating of the given enclosed space. Furthermore, medium sized residences, stores, and such other facilities are generally cooled / heated by small units operating in parallel. Operating multiple units together creates problems in control and cooperation of the units. To overcome such problems, two units are twinned and controlled together so that both units function identically providing more effective cooling/heating and avoiding large swings in room temperature.
Typically units are twinned / synchronized for improved airflow or to maintain adequate amount of air pressure. Twinning is used in applications where more heating or airflow capacity is needed than what one unit can deliver. Twinning is used to make two units operate in tandem, using a single duct system and a feedback system causing units to turn ON/OFF simultaneously.
To provide efficient cooling/heating, control systems are based on the characteristics of associated units as well as requirements of the enclosed space. Control systems typically communicate control information between twinned/synchronized units. In certain situations where units are located far away from each other, communicating control information between the twinned/synchronized units becomes more complex, especially if data is to be communicated on a single line. As units become even more sophisticated and perform more advanced functions, complexity of control systems and communication between the systems increase.

Hence, there is a need for a method that enables efficient communication of data between a plurality of units. Furthermore, there is a need for a method to effectively control units operating simultaneously including units which are located far away from each other. More particularly there is a need for a method that provides an effective solution for controlling multiple units operating simultaneously while enabling seamless transfer of information between the units.
OBJECTS
Some of the objects of the present disclosure aimed to ameliorate one or more problems of the prior art or to at least provide a useful alternative are listed herein below.
An object of the method of the present disclosure is to enable systematic, consistent and seamless communication of information on a single line between multiple units operating simultaneously.
Another object of the method of the present disclosure is to provide an efficient control of multiple units operating simultaneously.
Still another object of the method of the present disclosure is to provide an efficient control of multiple units which are located far away from each other.
Yet another object of the method of the present disclosure is to provide a communication method that can transmit unlimited amount of data between multiple units operating simultaneously.

One more object of the method of the present disclosure is to synchronize multiple units to provide a relatively more efficient cooling/heating of an enclosed space.
Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.
SUMMARY
In accordance with the present disclosure, there is provided a line communication method to communicate data over at least one wire line, between a plurality of units, each of the plurality of units being associated with a control system comprising a controller, the method including the following steps: providing a voltage signal to each controller; providing an input AC power supply to each of the plurality of units; conditioning each of the input AC power supplies to generate a conditioned reference signal for each controller; determining in phase or out of phase state of said conditioned reference signals by, feeding the conditioned reference signal to each controller, dividing the conditioned reference signal into a predetermined number of segments, each of the segments associated with a time period, generating a template signal frame and a data signal frame at predetermined segments of the conditioned reference signal, generating an interrupt signal in each controller on a first predetermined location on the conditioned reference signal, the interrupt signal being a reference point on each of the conditioned reference signals, the first predetermined location

being identical for each controller, logically ORing of the template signal frame and the data signal frame, transmitting the logically ORed signal over the at least one wire line, and analyzing the transmitted ORed signal relative to the reference point for detecting existence or non-existence of the template signal frame thereby determining the in phase or out of phase state of the conditioned reference signals; correcting the out of phase state of the conditioned reference signal, in the event that non-existence of the template signal frame is detected by shifting the interrupt signal, thereby the reference point of at least one controller to a second predetermined location on the conditioned reference signal, to align the reference point on each of the conditioned reference signals; and transmitting the data from the data signal frame of the phase corrected conditioned reference signal over the at least one wire line based on predetermined priority.
Additionally, the step of transmitting the data further includes the step of noise elimination by at least one method consisting of Cyclic Redundancy Check (CRC), checksum and parity bits.
Typically, the plurality of units is selected from the group consisting of HVAC units, furnace, air handler units, air conditioner units, heat pump unit and thermostats.
Typically, the controller is selected from the group consisting of microcontrollers, microprocessors, Application Specific Integrated Circuits (ASIC) and Digital Signal Processors (DSP).
Preferably, the template signal frame is a constant reserved data.

Typically, the data signal frame is a variable frame depending on the application of the unit and representing the data being transmitted.
Typically, the predetermined priority is determined by the controller and the data is transmitted by the unit having highest priority.
Preferably, the data transmitted over the at least one wire line is logical AND'ing of data transmitted by each of the plurality of units.
Alternatively, the controller assigns a pre-determined time slot to each of the plurality of units for transmitting the data in a circular manner or the data transmitted over the at least one wire line is queued data transmitted in a predetermined order based on the predetermined priority.
The method as envisaged in the present disclosure can be applied to twinned units or a plurality of units requiring communication of data for seamless, efficient transmission and / or control.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The method of line communication of the present disclosure will now be described with the help of the accompanying drawings, in which:
Figure 1 illustrates a schematic representation of simultaneous operation of two units in accordance with the present disclosure;
Figure 2 illustrates a graphical representation of data transmitted by a controller associated with each unit of Figure 1;

Figure 3 illustrates a graphical representation of frequency signal of an input alternating current (AC) power supply in accordance with an embodiment the present disclosure;
Figure 4 illustrates a flowchart representing the steps involved in phase detection and correction in accordance with an embodiment of the present disclosure; and
Figure 5 iJlustrates a graphical representation of phase detection and correction in accordance with an embodiment of the present disclosure.
DETAILED DESCRIPTION OF ACCOMPANYING DRAWINGS
The method of line communication of the present disclosure will now be described with reference to the embodiments shown in the accompanying drawings. The embodiments do not limit the scope and ambit of the disclosure. The description relates purely to the examples and preferred embodiments of the disclosed method and its suggested applications.
The method herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known parameters and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the

embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The following description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of a preferred embodiment, those skilled in the art will recognize that the embodiment herein can be practiced with modification within the spirit and scope of the embodiment as described herein.
Typically units are operated simultaneously for improved airflow and to maintain an adequate amount of air pressure. Simultaneous operation is used in applications where relatively more heating or airflow capacity is needed than what one unit can deliver. During simultaneous operation, two or more units operate in tandem using a single duct and feedback means, typically a thermostat that causes the units to turn ON/OFF simultaneously. At least a single wire line is required to convey information between units connected together. There have been many endeavors to provide an efficient means of communicating data between units operating simultaneously.

United States Patent US7377120 entitled "HVAC Twinning Control" discloses an approach for twinning of units. The system of the disclosure is specifically aimed at communication between two HVAC units. The disclosed system is thus limited to twinning applications. Again, data transmitted during a negative half of the line frequency is a duplicate of that transmitted during a positive half cycle. Hence restricted data is transferred in the disclosed system. The twinning method as disclosed is restricted to transmission of data in terms of PWM signals.
Thus, to overcome these shortcomings, the present disclosure envisages a method which provides an approach for transmitting data over at least a single wire line between a plurality of units operating simultaneously. The method of the present disclosure can be essentially divided into three main steps:
• Phase/Polarity Detection: A controller associated with each unit detects an in phase / out of phase state of an input AC power supply provided to each unit.
• Auto Phase Correction: If the input AC power supply is out of phase, the controller associated with each unit adjusts a reference point such that the signals are in phase.
• Data Communication: Various types of data can be communicated systematically between the plurality of units based on predetermined priority.
The description of the method in accordance with the present disclosure is provided based on Figures 1 to 5 and specifically referring to simultaneous operation of units, typically furnaces in the illustrated embodiment.

However, the method in accordance with the present disclosure is not limited to any specific application and can be adapted to transmit any type of data between any type of two or more units.
Referring to Figure 1, a schematic representation of simultaneous operation of two units in accordance with the present disclosure is illustrated. The system adopting the method of the present disclosure comprises two units (not shown), and a control system (A, B) associated with each unit, communicating with each other over a TwinLine (104). In accordance with an embodiment, the Twin_Line (104) comprises a single physical conductive wire. However, the Twin_Line (104) may include more than one physical conductive wire. The Twin_Line (104) is connected to a Twin_Connector (103) on each control system (A, B). The control system (A, B) associated with each unit is individually connected to a voltage supply denoted by TwinJVoltage (105). The control system (A, B) comprises a controller (110A, HOB) and a switching device denoted by Q for switching the TwinJVoltage (105) to ground. The controller (110A, 110B) comprises an input port pin, Twin_In pin (101) and an output port pin, Twin_Out pin (102). Optionally, the control system (A, B) comprises a signal conditioner (106) connected to Twin_In pin (101) for conditioning the signal to be read by the controller (110A, HOB) for further processing. TwinJVoltage (105) is typically any voltage understandable by the microprocessor. In accordance with an embodiment, the TwinJVoltage (105) is a Direct Current (DC) voltage supply. In order to transmit information, the controller (110A, HOB) drives the Twin_Out pin (102). The controller (110A, HOB) reads the data on Twin_Line (104) with the help of Twinln pin (101). Data on the TwinLine (104) is represented by

the presence or absence of Twin_Voltage (105). Furthermore, the presence or absence of Twin_Voltage (105) on the TwinJLine (104) is also decided by the controller (110A, HOB) by means of the switching device Q. In accordance with an embodiment, the switch Q is at least one of a Bipolar Junction Transistor (BJT) or a Field Effect Transistor (FET) or a semiconductor transistor. The operation of the switch Q is controlled by the controller (110A, HOB) by driving the Twin Out pin (102). Presence of TwinVoltage (105) on the Twin_Line (104) is represented by binary signal "1" or logic HIGH. Absence of Twin_Voltage (105) on the TwuiLine (104) is represented by binary signal "0" or logic LOW. A reference AC power supply is provided to each controller (110A, HOB) associated with each unit, to generate a reference for data to be transmitted. The reference AC power supply is attenuated and conditioned to a suitable level thereby enabling the microprocessor to read it.
Referring to Figure 2, a graphical representation of data transmitted by the controller (110A, HOB) over a wire line is illustrated. In accordance with one embodiment, inverting logic is used wherein the data read by Twinln (101) is inverse or complement to the data transmitted on TwinOut (102) to drive TwinOut (102) and control/actuate the switch Q. Alternatively, non-inverting logic is used whereby data read by Twin_In (101) is the same as data transmitted on Twin_Out (102) control the operation of switch Q. Since both the controllers (110A, HOB) share a common Twin_Line (104), when data is transmitted simultaneously, the resultant data is logical AND'ing of the data from the individual units, wherein LOW signal overrides HIGH signal. In accordance with another embodiment, the resultant data can be any logical boolean operation performed on the data.

As indicated in table 1 herein below, the resultant data (column C5) on TwinJLine (104) is logical AND'ing of data transmitted by the controller 110A (column C2) and the controller 11OB (column C4),

CI C2 C3 C4 C5
Controller (110A) Controller (HOB) Resultant data
TwinOut Twin_Line (Ideally) TwinOut TwinLine (Ideally) TwinLine (Actually)
0 1 0 1 1
0 1 1 0 0
1 0 0 1 0
1 0 1 0 0
Table 1
Referring to Figure 3, a graphical representation of frequency signal of an input alternating current (AC) power supply in accordance with an embodiment the present disclosure is illustrated. Data (D) on the TwinLine (104) is transmitted and monitored with respect to the reference AC power supply frequency signal (S). The reference AC power supply frequency signal (S) is divided into a predetermined number of equal time segments to constitute a frame comprising a predetermined number of bits. In accordance with one embodiment, if the reference AC power supply frequency signal (S) is 60 Hz, then dividing the reference AC power supply frequency signal (S) into sixteen equal segments forms sixteen bits, with bit period for each bit being 1 millisecond (ms) thereof. The number of bits and the duration of bit period depend upon the integer number by which the AC power supply

frequency is divided. The number of bits and the duration of bit period is predefined based on requirement. For a predefined bit period, the presence of TwinVoltage (105) on the Twin_Line (104) is represented by binary signal "1" or logic HIGH and absence of TwinJVoltage (105) on the Twin_Line (104) is represented by binary signal "0" or logic LOW. The data on the Twin_Line (104) is transmitted and received with respect to a common reference point on the reference AC power supply frequency signal (S). In accordance with one embodiment, a common reference point is the zero crossing point of the AC power supply frequency signal (S) and typically, an interrupt signal is generated at the zero crossing point of AC power supply frequency signal. Alternatively, any point on the AC power supply frequency signal can be used as a reference point and an interrupt signal can be generated accordingly. For comparing and detecting an in phase / out of phase state of the AC power supply frequency signal (S) on all units, it is essential that the reference point on the AC power supply frequency signal (S) of all units are identical.
In order to determine whether the reference AC power supply frequency signal in all the units is in phase or out of phase with each other, a data frame denoted by DataSignalFrame (DSF) and a template frame denoted by Template_Signal_Frame (TSF) are identified from the segments formed by dividing the AC power supply frequency signal (S).The DataSignalFrame (DSF) and the Template_Signal_Frame (TSF) are logically OR'ed and transmitted on the Twin_Line (104). The Data_Signal_Frame (DSF) is a variable frame depending on the application of the unit and representing data being transmitted on the Twin_Line (104). The Template_signal_frame (TSF) is a constant reserved data.

In accordance with the illustrated embodiment, the TemplatejSignalFrame (TSF) comprises two bits, wherein bit positions 6 and 7 during a positive cycle of the reference AC power supply frequency signal (S) and bit positions 14 and 15 during a negative cycle of the reference AC power supply are reserved for the Template_Signal_Frame (TSF), from the sixteen bits formed by dividing the reference AC power supply frequency signal (S). The other bit periods forming the DataSignalFrame (DSF) are denoted by 'X' (referring to a 'don't care' condition being either '0' or '1'). Alternatively, the Template_Signal_Frame (TSF) is formed at any predetermined bit position and can be of any pre-defined signal level. When the data transmitted on TwinLine does not contain a Template_Signal_Frame (TSF), it is concluded that the reference AC power supply frequency signal (S) of that particular unit is out of phase.
In practice, phase of AC power supply frequency is changed when physical connections of the supply are swapped. Although, such an occurrence is difficult to predict, the method in accordance with the present disclosure is capable of taking corrective action if such a swapping does occur accidentally.
Figures 4 and 5 illustrate a flowchart representing the steps involved in phase detection and correction and a graphical representation of phase detection and correction in accordance with an embodiment of the present disclosure respectively. When data is transmitted on the Twin_Line (104), the controller (110A, HOB) associated with each unit on the TwinLine (104) analyses the data by trying to identify the Template_Signal_Frame (TSF) OR'ed with the Data_Signal_Frame (DSF) in the received data. If the

received data does not contain a TemplateSignalFrame (TSF), the controller (110A, 11 OB) associated with the corresponding unit concludes that the reference AC power supply is out of phase and shifts its interrupt (I) edge. As shown in Figure 5, bit positions 6, 7 and 14, 15 are reserved for the Template_Signal_Frame (TSF). The controller (110A, HOB) associated with both the units checks for a LOW or "0" signal at bit positions 6, 7 and for a HIGH or "1" signal at bit positions 14, 15. If the controller is not able to detect a LOW or "0" signal at bit positions 6, 7 and a HIGH or ''1" signal at bit positions 14, 15, the controller (110A) concludes that the reference AC power supply frequency signal (Wl) of the unit associated with the controller (110A) is out of phase with the reference AC power supply frequency (W8) of the unit associated with the controller (11 OB). In accordance with one embodiment, the interrupt (I) is provided on the rising edge of the zero crossing point of the reference AC power supply frequency (W2, W9). The interrupt (I) serves as a reference point for the controllers (110A, HOB) and initiates counting of the bit positions from thereon. Since the reference AC power supply (Wl and W8) of both the units are out of phase, the bit position '0' on Wl, W2 corresponds to the bit position '8' on W8, W9. As a result, the reference points (I) for the controller (HOA) and controller (11 OB) are different. Both the controllers (110A. HOB) have to transmit data OxFCFF (W3) containing TemplateSignalFrame (TSF) at bit positions 6, 7, 14, 15 and Data_Signal_Frame (DSF) at the remaining bit positions. However, since the reference points (I) for each of the controllers (1 l'OA, 110B) are different, the controller (HOB) generates OxFFFC (W10) and the resultant signal appears on the TwinLine (104) as OxFCFC (W4, Wll). When the controller (110A) completes checking its bit position 15, the controller (HOB) would still be checking its bit position 7. As a result

the controller (110A) would conclude that the data received at bit positions 14 and 15 is not the same as the data transmitted. Accordingly, the controller (110A) shifts its interrupt (I) edge from the rising edge of the zero crossing point of the reference AC power supply frequency signal (W5, W6) to the falling edge of the zero crossing point of the reference AC power supply frequency signal (W12, W13). As a result, the data in bit positions 40' to '15' of both the controllers (110A and HOB) are same (W6, W13), leading to a successful transmission of data (W7, W14) on the TwinLine (104).
Thus using the aforementioned method, a controller associated with a unit can reverse its TemplateSignalFrame (TSF) to nullify the action of shifting of the interrupt edge (I) as explained herein above. Practically, there is a time difference of half cycle or 8 ms in the reference AC power supply (60Hz frequency) signal of the two units which are out of phase. The time difference depends on the frequency and would accordingly vary for a 50Hz reference AC power supply. Shifting the interrupt (I) edge creates a common reference point resulting in all the controllers having an identical Template_Signal_Frame (TSF) embedded in the transmitted data on the Twin_Line(104).
The method of communication between simultaneously operating units of
the present disclosure can be divided into three layers,
• Physical layer - A physical layer comprises hardware as discussed in the aforementioned control systems (A, B). The control systems (A, B) associated with both the units communicate with each other through the physical layer on a physical medium.

• Data Link layer - Data link layer provides a functional and procedural means to transfer data between the controllers (110A, HOB). Additionally, the data link layer provides means to detect and possibly correct errors that may occur in the physical layer. When the controllers (110A, HOB) attempt to use the Twin_Line (104) simultaneously, frame collisions occur. The data-link method specifies a means for the controllers (110A, 110B) to detect and recover from such collisions, and further provide methods to prevent them. Furthermore, the data link layer provides acknowledgements and re-transmission of data. The basic services provided by the data link layer include auto phase detection, auto phase correction and optionally Cyclic Redundancy Check (CRC), checksum and parity bit check.
• Application layer - Application layer comprises different applications based on the requirement.
Referring to Figure 3, the 60 Hz reference AC power supply frequency signal (S) is divided into sixteen equal segments to constitute a frame comprising sixteen bits, with bit period for each bit being 1 ms thereof. In accordance with one embodiment, duration of each bit period is used to transmit the speed of operation of a unit. Thus, l/16t of 60 Hz time duration in each cycle is used to transmit the speed of operation of a unit. To calculate the number of speed related data, it is assumed that 'n' denotes the number of speed related data that is transmitted and duration 't' denotes the time period to transmit one speed related data. Since the bit period for each bit is 1 ms, each cycle of the 60 Hz AC power supply frequency signal (S) constitutes 16 ms time frame. During both the positive and negative half cycles, the data transmitted would be 'nt\ Furthermore, a different set of

data would be transmitted during each half cycle. Thus, for a 16 ms time frame, the data transmitted can be represented by,
nt= 16 wherein t = 1 ms, n = 16 However, four bits represented by Template_Signal_Frame (TSF) are used for phase detection and correction. Therefore,
n= 16-4= 12 Thus, 12 different speed related data can be transmitted using the method of the present disclosure. Thus the method of the present disclosure for transmitting speed related data of a unit has a distinct advantage over the methods known in the art.
The method of the present disclosure can be adapted to other applications but not limited to the applications listed herein below.
• The method of the present disclosure can be used for simultaneous operation of fixed speed units as well as variable speed units by simultaneously communicating the speed of the units in Cubic Feet per Minute (CFM).
• The method of the present disclosure can be used to provide an alert if variable speed units are used (to stop the operation).
• The method of the present disclosure can be used to synchronize the direction of operation of different units operating simultaneously.
• The method of the present disclosure can be used for communicating any type of data between at least two units by incorporating at least one of the following fields in the aforementioned communication method - unit number, message number, data length, CRC, and parity field.

Unit Number Data Length Object Number Data CRC
• The method of the present disclosure can be used for communicating data of any amount or size.
• The method of the present disclosure can be used for communication at any baud rate and is applicable for low baud rate communication also.
• The method of the present disclosure can be used for communicating data between units located far away from each other by using at least one physically conductive wire connection.
Different units can communicate with each other in accordance with various embodiments of the communication method described above.
• A master-slave communication method can be used by different units to communicate with each other.
• A communication method having run time arbitration can be used by different units to communicate with each other. The unit having high priority would be able to gain access and transmit data on the communication line.
• A message driven communication method can be used by different units to communicate with each other. The message having high priority would be able to gain access and transmit data on the communication line.
• A communication method wherein each unit would transmit data in a circular fashion can be used by different units to communicate with each other. Each unit would have an allotted time slot for transmitting the data.
• A communication method wherein data transmitted is queued data transmitted in a predetermined order based on predetermined priority.

Thus the approach of the method of the present disclosure is not just limited to simultaneous operation of multiple units but can be used as a communication method to convey various types of data such as temperature, CFM data and the like by using different embodiments of the method of the present disclosure. The method of the present disclosure alleviates most of the problems of the prior art leading to a more efficient simultaneous operation of multiple units and a reliable method to communicate any type of data.
TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE
The technical advancements offered by the method of the present disclosure include the realization of:
• different units operating simultaneously at different speeds;
• AC power supply phase detection and auto correction;
• simultaneous operation of multiple units located far away from each other;
• simultaneous operation of variable speed units as well as fixed speed units;
• provision of alerting means if variable speed units are used when operating simultaneously;
• synchronized direction of operation of different units operating simultaneously;
• unlimited amount of data to be communicated;
• usability in different applications as a communication method to convey any type of data for any operation; and

• usability for communicating data between different units located far away from each other by using at least one physically conductive wire connection.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements, as the use may be in one of the embodiments to achieve one or more of the desired objects or results.
Any discussion of documents, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.

The foregoing description of the specific embodiment will so fully reveal the general nature of the embodiment herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiment without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiment. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiment herein has been described in terms of preferred embodiment, those skilled in the art will recognize that the embodiment herein can be practiced with modification within the spirit and scope of the embodiment as described herein.

We Claim:
1) A line communication method to communicate data over at least one wire line, between a plurality of units, each of the plurality of units being associated with a control system comprising a controller, said method comprising the following steps:
• providing a voltage signal to each controller;
• providing an input AC power supply to each of the plurality of units;
• conditioning each of the input AC power supplies to generate a conditioned reference signal for each controller;
• determining in phase or out of phase state of said conditioned reference signals; said step of determining further comprising the following steps:
feeding said conditioned reference signal to each controller;
dividing said conditioned reference signal into a predetermined
number of segments, each of said segments associated with a time
period;
generating a template signal frame and a data signal frame at
predetermined segments of the conditioned reference signal;
generating an interrupt signal in each controller on a first
predetermined location on the conditioned reference signal, the
interrupt signal being a reference point on each of the conditioned
reference signals, said first predetermined location being identical
for each controller;
logically ORing of said template signal frame and said data signal
frame;

transmitting the logically ORed signal over the at least one wire line; and
analyzing the transmitted ORed signal relative to said reference point for detecting existence or non-existence of said template signal frame thereby determining the in phase or out of phase state of said conditioned reference signals;
• correcting the out of phase state of the conditioned reference signal, in
the event that non-existence of said template signal frame is detected;
said step of correcting further comprising the following step:
shifting the interrupt signal, thereby said reference point of at least one controller to a second predetermined location on the conditioned reference signal, to align said reference point on each of the conditioned reference signals; and
• transmitting the data from said data signal frame of the phase
corrected conditioned reference signal over the at least one wire line
based on predetermined priority.
2) The line communication method as claimed in claim 1, wherein the step of transmitting the data further comprises the step of noise elimination by at least one method consisting of Cyclic Redundancy Check (CRC), checksum and parity bits.
3) The line communication method as claimed in claim 1, wherein the plurality of units is selected from the group consisting of HVAC units, furnace, air handler units, air conditioner units, heat pump unit and thermostats.

4) The line communication method as claimed in claim 1, wherein the controller is selected from the group consisting of microcontrollers, microprocessors, Application Specific Integrated Circuits (ASIC) and Digital Signal Processors (DSP).
5) The line communication method as claimed in claim 1, wherein said template signal frame is a constant reserved data.
6) The line communication method as claimed in claim 1, wherein said data signal frame is a variable frame depending on the application of the unit and representing the data being transmitted.
7) The line communication method as claimed in claim 1, wherein said predetermined priority is determined by the controller and said data is transmitted by the unit having highest priority.
8) The line communication method as claimed in claim 1, wherein the data transmitted over the at least one wire line is logical AND'ing of data transmitted by each of the plurality of units.
9) The line communication method as claimed in claim 1, wherein the controller assigns a pre-determined time slot to each of the plurality of units for transmitting the data in a circular manner.
10) The line communication method as claimed in claim 1, wherein the data
transmitted over the at least one wire line is queued data transmitted in a
predetermined order based on said predetermined priority.

11) A system comprising at least two units communicating data based on the line communication method as claimed in claim 1.