Title of Invention

"A DEVICE USEFUL FOR TRANSMITTING STANDARD TIME OVER A TELEPHONE NETWORK"

Abstract

A device useful for transmitting standard time over a telephone network which comprises a pluse qenerator(l) capable of being synchronized with a standard external clock, characterised in that the output of the said generator(l) being connected directly through an I/O interface (3) to a CPU (2) having RAM and EPROM, the said CPU(2) being connected to a key board(7) and to a digital display unit (5) through an interface(4) the said CPU(2) being connected to an interface (6) capable of making the signals compatible for connecting to a telephone modem.

Full Text

This invention relates to a device useful as a master/slave clock for transmitting and receiving standard time over a telephone network and a telephone network incorporating the device for transmitting and receiving standard time. Requirement of very precise time (of the order of milliseconds, microseconds , nanoseconds etc.) is limited to users engaged in research in basic science, astronomical studies, space mission, defence activities, etc. But other than these, most of users who are interested in time up to one second accuracy would be interested for such service. Number of such users are numerous including organizations which arrange public display system for time like Railway Station, Airport, Some Supermarket, some government organizations etc. Time is one of the several basic quantities from which most physical measurement systems are derived. Others are length, mass and temperature. Unlike other physical quantities it cannot be apprehended by any of the physical senses. For example, we can see distance, feel weight or temperature. But we can know time only through consciousness or observing effects. When we talk of 'time' it may have two meanings: (i) time interval and (ii) time instant. Therefore, the word time requires some additional terms for clarifications. The first one, i.e. the time interval is the duration between two events, or in other words, it is the length of time between two events. Time interval may or may not be associated with a specific date. It is of vital importance for synchronization, the very basic need for efficient communication. The second one, the instant of time, specifies the particular time at which an event has occurred or will occur. Time of a day or date is the most often used term and that is usually presented in a brief form of Hours, Minutes and Seconds,whereas a complete statement completes the week, month and year. It could also extend to units of smaller than the seconds going down through milliseconds, microseconds, nanoseconds and picoseconds. We can define time as a continuum which lacks spatial dimensions and in which events occur through irreversible succession from past to future through present. Accurate and precise means for time information traceable to national and international standards have assumed great importance in recent times. This is due to the demanding uses in various fields. Dissemination means interconnections between the source and the user of time signal. This is like a bridge to make connection between them. Hence to make time accessible to the users the need for time dissemination emerges. There are different types of users depending on the accuracy desired by them. The accuracy desired by them may be of the order of nanoseconds, picoseconds, microseconds, milliseconds and seconds. As the requirement of the order of time accuracy increases the system becomes more and more complicated and at the same time the cost of the system also increases. The system which can provide highest order of accuracy obviously can serve the purpose of the users requiring lesser order of accuracy. But the use of such a system for the purpose where lower order of accuracy is desired would unnecessarily complicate the system and at the same time the system would be very expensive which is quite undesirable. So, there are several methods of time dissemination having their relative merits and demerits depending mainly on its accuracy, coverage, reliability, ease of use and cost etc. Basic methods of Standard Time and Frequency Signal (STFS) dissemination may be broadly classified into following categories: Portable Clocks : It is the most accurate and reliable method of time transfer from the time keeping laboratory to the remote user. In this method a portable clock is synchronized at a reference station and carried to desired place in running condition for comparison. To synchronize a remote clock it becomes imperative to fly the clock to reduce travel time. Thus, this method is expensive and is available on demand. But this method is accurate to some tens of nanoseconds. III. Radio Communication: It is the most important method of STFS dissemination. This dissemination technique is used for comparison of remote clock through radio signal. Previous methods are basically meant for point to point communication. But the radio technique has the primary provision of many users' accessibility simultaneously. The radio communication involves ionospheric propagation up to frequencies of 30MHz.If the frequency exceeds 30MHz, the wave propagates in almost a straight line. This is called line of sight propagation (LOS) and forms the basic feature of TV and satellite systems. The satellites are more advantageous than the terrestrial STFS dissemination techniques in terms of global coverage, accuracy of time transfer and propagation feature. Radio communication can be classified as: A. High Frequency System B. Very Low Frequency System C. Satellite System: There are two main categories of STFS dissemination through satellites e.g. (a) Geostationary satellites: Geostationary Satellites are normally used to reflect the time signals. There are two basic techniques of time transfer via Geostationary satellite: (i) Two way technique : Two way technique using mitrex modem has been used for experimental purposes many time to synchronize/compare phasing of seconds pulses of clocks remotely located. This technique amply showed the capability of time comparison accuracy of the order of tens of nanoseconds . (ii) One way technique : There are two standard time and frequency signals (STFS) dissemination service in one way mode which are operational - one via INSAT originated from National Physical Laboratory, India and the other is via GOES satellite originated from Standard Time, USA. The time service via INSAT has the time accuracy capability of ten microseconds. (b) GPS System: Global Positioning System (GPS) is the most accurate world wide time service. This has the capability of few hundred nanoseconds time at any time everywhere. Wire Communication : Wire communication means to transmit clock time through wire cables. These are used for driving different clock display systems from one central clock for in-house applications. There are two types of wire communication: Parallel Bit Communication : In this form of wire communication one should dedicate one line for each bit of information, thus requiring N lines for N bits. This is the major disadvantage in parallel communication. Thus dissemination of time signals in parallel form is rather inconvenient for longer distance. But circuit for display system is simple and faster. Serial Bit Communication : In this case of serial cables there is a pair of wires instead of parallel wires. So bits related to current time data is transmitted sequentially i.e. one bit at a time is transmitted. This is a slow process and is used in fields where speed is not an important factor. Here circuit is more involved and thereby involve some cost. But this is convenient for longer network. These techniques might have been used for local applications but no regular time service using these techniques has been reported yet now. Most of the available services give time accurate to the order of milliseconds , microseconds, submicroseconds etc., thereby making it economically nonviable for large number of users, requirement. None of the above mentioned service can serve the requirement of Standard Time display with a very simple and inexpensive means. Teleclock services which is being planned to be launched by the applicants would be a service through which users would be accessed to Standard Time up to one second accuracy with a very simple equipment connected to normal P&T telephone line.This service would be the first of its kind and would be known as TELECLOCK SERVICE. The main object of the present invention is to provide a device useful as a master/slave clock for transmitting standard time over a telephone network . Another object is to provide a telephone network incorporating the device for transmitting and receiving standard time. In the present invention synchronization of time is being done through telephone lines. Here digital data is being generated from a standard clock and is transferred through a telephone line. The users may get their clock synchronized to Standard Time by dialing the number of the dedicated telephone line. The system has its own independent clock based on a good crystal oscillator, which is sufficient to maintain time within one second for a day or two. It has its own automatic dialling arrangement through a modem. It can dial the number and get its clock synchronized to the data transmitted by the master clock kept at a certain place through a telephone line within a couple of seconds. The clock of the user will then run from its new time automatically as soon as the telephone line is disconnected. In fig. 1 of the drawings accompanying this specification the block diagram of the device of the present invention which is useful as a master/slave clock is depicted. In fig. 1, block 1 is a pulse generator, block 2 is a central processing unit (CPU) with Random Access Memory (RAM) and Externally programmable read only memory (EPROM) , block 3 is an input/output (I/O) interface, block 4 is a key board / display interface, block 5 is display unit, block 6 is an interface and block 7 is a key board. Accordingly, the present invention provides a device useful for transmitting standard time over a telephone network which comprises a pulse generator(l) capable of being synchronized with a standard external clock , characterised in that the output of the said generator(l) being connected directly through an I/O interfaced) to a CPU (2) having RAM and EPROM, the said CPU(2) being connected to a key board(7) and to a digital display unit (5) through an interfaced), the said CPU(2) being connected to an interface (6) capable of making the signals compatible for connecting to a telephone modem. The central processing unit used may be a microprocessor such as Intel (8085,8080,8086), Motorola(68000). In fig. 2 of the drawings accompanying this specification, the block diagram of the telephone network incorporating the device for transmitting and receiving standard time is shown. In fig.2, block 8 depicts the master clock the details of which is shown in fig. 1 of the drawings, block 9 is a modem, block 10 is an electronic switch. Accordingly the present invention provides a telephone network incorporating the device for transmitting and receiving standard time which comprises a master/slave clock (8) connected to a telephone network through a modem(9) and an electronic switch(10) at the transmitting end, a slave clock at the receiving end being connected to the said telephone network through a modem(9). The device of the present invention is a microprocessor based system. The system , therefore, functions through a software which is intimately related to its hardware arrangements. When the clock is in the master mode, the master clock sends out data related to current time through the RS232C port in a definite format so that the receiving slave clock can recognize the pattern. The sequence of characters and data those are sent are as follows: "O", "", "" , SD, "" , "K", "", MD, "", "G", "", HD. Items within the " " are characters themselves and SD, MD and HD correspond to two digit data of second, minute and hour respectively. "" denotes the "command character" carriage return. The arrival of "O" signifies the phase of the second pulse of the master clock, "O" is received by the slave clock by hardware means. So customarily one software pulse through anyone port of IC8255 would be generated immediately after the identification of "O". This software pulse aligns the phasing of lpps generation to interrupt RST 6.5 at the receiving end. The technique involved is simple. A crystal oscillator output has to be passed through a frequency divider chain to get the lpps signal. In this case the dividing counter is started by the incoming MASTER clock's lpps and after pulse shaping, we get a phase shifted lpps in the SLAVE clock. "S", "K" and "G" are signature that precedes the second data (SD), minute data (MD) and hour data (HD) respectively. In the case of clock operating in the slave mode, it receives the data stream from the RS 232C port. Since the data is transmitted serially and the pip can start intercepting data from any point, the necessity of the signature is felt. That is, when any of this signature is recognised, the following two digits would be assumed to be the corresponding hour, minute or second data. The above data sequence is repeated four times in a second in order to provide enough redundance and confidence in reliability of the data at the receiving end. The carriage return "" is not necessary if the receiving end is a slave clock but it is convenient when a computer's internal clock is to be synchronized. However the software is not unduly complicated due to its presence. In order to make the data format universally compatible is added after each data. The slave takes two sets of data pertaining to current time out of the transmitted five sets of data in a second. It compares the two sets. If any discrepancy is found it throws the whole data and starts afresh. The following example is given by way of illustration of the device of the present invention and it should not be construed to limit the scope of the present invention. 1 PPS Generation Unit : The lpps is actually generated from a 5MHz signal. A cascade of frequency divider are used to generate lpps from 5MHz. Here as a frequency divider we have used IC7490 which is a decade counter. The divider chain has the provision of being reset by a software lpps and/ or hardware lpps available from the external source. The software pulse helps in aligning the phase of the in built lpps with that of the received lpps. This alignment helps in extracting data from the received signal as will be more clarified in the software section. The system has in built 5 MHz fairly accurate quartz crystal oscillator. Here Phase Locked Loop (PLL) chip IC564 has been used instead of a simple quartz crystal oscillator. The advantage of using the PLL is the following. If the users have a better frequency source of 5 MHz, it can be fed to input of the PLL to lock the VCO frequency. Thus the generated lpps becomes more accurate. In the absence of a better external source, VCO of the PLL would anyway behave as a simple oscillator. The lpps generated by the hardware as described above is used to interrupt RST 6.5 of the fiP. Microprocessor related unit : The system is based on an 8-bit microprocessor. The functional block diagram of the system is shown in Fig 1 of drawings. The main operation of the microprocessor is in its interrupt mode. The interrupt pulse required to run the software is fed from the lpps signal generator. The microprocessor based clock system is made compatible to other digital systems like computers by the provision of a standard RS232C port through an interface (block 6) by utilizing SOD (serial output data) port and SID (serial input data) of the CPU (block 2). The functional block diagram of the master/slave clock of the drawings shown in fig. 1 comprises of the following main components : (i) the Intel 8085 Microprocessor chip (ii) 8279 Keyboard/ Display interface chip (iii) 8255 I/O interface chip (iv) RS232C interface chips - 1488 and 1489 The RS 232 interfacing is done through 2 pins of the 8085µP. These two pins are the serial I/O pins. Since the RS 232 is not compatible with TTL logic so we have used the line drivers IC1488 and the line receivers IC1489 for interfacing TTL logic with RS 232. The serial data out of SOD of µP 8085 is of TTL logic level. In order to make this TTL logic compatible with RS 232 it is converted to RS 232 by IC 1488. The output voltage level of the line driver is decided by its power supply. The received RS 232 signal is converted to TTL logic by the IC 1489 and is fed to the line of the µP 8085. Thus the RS 232 is made compatible with the TTL logic using 1488 and 1489 ICs. 8255 is a general purpose I/O interface . It has been configured for only output port. C-low port of 8255 is used for the generation of lpps by software means. The 8279 is used for interfacing keyboard/ display. This is done by software means. When data is entered through keyboard, it is stored in the internal FIFO (First In First Out) memory and an interrupt signal is generated with each entry. This interrupt signal is used to interrupt RST 5.5 of the 8085 µP. The software for running the keyboard interface is written in the ISS of the RST 5.5. The display unit is an eight unit seven segment LED. These are used to display the current time and the status of the different mode of operation through pre-assigned character. Software Details: The software of the system of the present invention comprises of the main program and two Interrupt Service Subroutine (ISS) RST 6.5 and RST 5.5. The main program after initializing process enables the interrupts RST 6.5 and RST 5.5 and receives the data from serial port if desired. The initializing process consists of configuring I/O interface 8255, suitably setting the memory areas and setting the current time through the key entry if required. After enabling the interrupts the program lies in a wait loop with a provision of routing thorough the slave program whenever necessary. In the slave program first the signature of the incoming data is checked. If the incoming signature is "S" then the following data is stored as the second data. Thus after the identification of the signature of "K" and "G" , the minute and hour data are stored respectively. These stored data are used as valid data for time till two consecutive sets of data match exactly. The lock flag is set after the availability of valid data. The basic clock of the system is a software clock run in the interrupt mode through RST 6.5. The RST 6.5 is activated by a lpps signal generated by hardware as described earlier. The ISS RST 6.5 updates the clock. One may set the time according to the key entry. In this ISS program, the data stream following the transmission scheme (explained earlier) is outputted through the SOD port when the system operates in the master mode. The ISS RST 5.5 is executed on entering data through the key board. RST 5.5 ISS actually stores the keyed data in the desired area. The ISS is written in such a way that on pressing the letter "E" the last three data set entered will be displayed on the eight unit 7-segment LED. This has been implemented by the interfacing of µP 8085 with the 8279. While executing RST 5.5 if lpps signal arrives then it jumps to RST 6.5 and the program returns back to ISS 5.5 after executing the RST 6.5 . The main advantages of the present invention are: 1. Time display of Standard Time such as 1ST corrected upto one second is always available. 2. The time is corrected through "normal telephone network in a auto-dialing on command. 3. This is a very simple and inexpensive system. 4. It has independent clock built into the system. 5. The Quartz crystal oscillator of the clock is quite stable to maintain the time within a couple of seconds for a week. 6. The system is compatible with localized telephone network or standard country wide telephone system. 7. The system is compatible with available standard telephone modem. Claim: 1. A device useful for transmitting standard time over a telephone network which comprises a pulse generator(l) capable of being synchronized with a standard external clock , characterised in that the output of the said generator(l) being connected directly through an I/O interface(3) to a CPU (2) having RAM and EPROM, the said CPU(2) being connected to a key board(7) and to a digital display unit (5) through an interfaced), the said CPU(2) being connected to an interface (6) capable of making the signals compatible for connecting to a telephone modem. 2. A device as claimed in claim 1 wherein the central processing unit (CPU) used is a microprocessor such as lntel(8085,8080,8086), Motorola (68000). 3. A device useful for transmitting standard time over a telephone network substantially as herein described with reference to fig. 1 of the drawings accompanying this specification and the example.

Documents:

2472-del-1995-abstract.pdf

2472-del-1995-claims.pdf

2472-del-1995-complete specification (granted).pdf

2472-del-1995-correspondence-others.pdf

2472-del-1995-correspondence-po.pdf

2472-del-1995-description (complete).pdf

2472-del-1995-drawings.pdf

2472-del-1995-form-1.pdf

2472-del-1995-form-2.pdf

2472-del-1995-form-3.pdf

2472-del-1995-form-4.pdf

2472-del-1995-petition-others.pdf

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