CA1233516A - Memory interface for electronic demand register of an electric meter - Google Patents

Abstract

MEMORY INTERFACE FOR ELECTRONIC DEMAND
REGISTER OF AN ELECTRIC METER

ABSTRACT OF THE DISCLOSURE

An electronic demand register for an electric meter includes a volatile storage for normal processing of data and a non-volatile storage into which data is serially written upon the occurrence of conditions which may threaten the integrity of such data and from which the data is again retrieved when the condition no longer exists. The data formats for transmission of the data to the non-volatile memory and for receiving it therefrom do not agree with the data formats which the volatile storage must have. A communications buffer assembles a data package for transmission to the non-volatile memory which has a format which can be suitably serially transmitted to the non-volatile memory and be properly interpreted there due to the manner in which the non-volatile memory recognizes and stores data. In addition, the communications buffer receives the serial data from the non-volatile memory and, by left shift and selection of only valid portions of the data, assembles data suitable for transmission to the volatile memory.

Description

335~Ç~

M~ORY INTE~FACE FOR ELECTRONIC DEMAND
__.___ REGISTER OF AN ELECT~IC METER
__ _ ___ BACKGROUND OF THE INVENTION
The present invention relates -to el~c-tric meters and, more par-ticularly, to a memory interface for electronic demand registers of electric meters.
Conventional electric meters employ an aluminum disk driven as a rotor of a small induction motor by an electric fleld at a speed which is proportional to the electric power being consumed by a load. Geared dials, or cyclometer discs, integrate the disk motion to indicate the total energy consumed, conventionally measured in kilowatt hours tone kilowatt hour equals one thousand watts o~ power consumption for one hour).
In adclition to the above measurement of consumption, some electric meters contain means for separating the consumption into those parts of consumption occurring cduring peak and of~-peak hours (however defined) and for recording maximum demand during a predetermined periocl of time in order to adjust billing according to such parameters. In one such demand meter disclosed in U.S.
Patent 3,586,97~ - D. M. Ham et al issued June 22, 1981, a mechanical demand register records the power usage during a predetermined period of time and stores -the value for reading. The predetermined period of time may be, for example, the time between meter readings, or a .~

~ ME-137 perio~l of time corresponding to the billing period of the utility providing the power. A clockwork mechanism res-tarts -the demand register at regular intervals of, for example, a fraction of an hour, so S that, at the end of the predetermined period, the stored value represents the highest value of power u~age occurring during any one of the regular intervals in the predetermined period.
Delnand registers of the mechanical ty~e, 0 such as di~closed in the above U.S. Patent, have limited flexibility. Once their design is complete(l for a particular meter physical confiyuration, -the design is not transEerable -to a meter having a different physical configuration. In addition, the demand-measurement functions cannot be redefined withou-t major mechanical redesign.
Greater flexibility may be obtainable using electronic acquisition, integration and processing o~
power usa~e. An electronic processor such as, for example, a microprocessor, may be employed to manage the acquisition, s-torage, processing and display of the usage and demand data. U.S. Patents 4,179,654 -W. R~ Jenmer issued December 18, 1979; 4,197,582 -P. M. Johnston et al issued April 8, 1980; 4,229,795 - J. Vieweg et al issued October 21, 1980; ~,283,772 - P. M. Johnston issued August 11, 1981; 4,301,508 -J. A. Anderson issued November 17, 1981; 4,361,872 -A. Spa:Lti issued November 30, 1982; and 4,368,5L9 --S. P. Kennedy issued January 11, 19~3, among others, illustrate the Elexihility that electronic processincJ
brings to the power and enerc3y usage measuremerlt.
Each of -these electronic measurement devices includes means for producing an electronic signal ihaving a characteristic such as, for example, a frequency or a pulse repetition rate, which i9 related -to the rate of power usage. ~le electronic processor i~ substituted 5~6 - 3 ~ ME-137 for the mechanical demand register of the prior art to keep track of the power usage during defined periods of -time.
~n electronic processor of an electronic demand register conventionally employs volatile random access memory for the hlyh speed and low power consumption characteris-tics offered by such devices. However, several events can occur during normal and emergency conditions which can threaten the integrity of data belng recorded for billing purposes in volatile random access memory. If a power outage, by removing power from the processor and the random access memory, were allowed to erase all data stored in random access memory, then the billing data contained in the erased data would be lost. This is, of course, unacceptable.
Some means, there-fore, appears desirable for storing data in non-volatile memory when a power outage occurs.
On the converse, certain normal deviations of the line power, such as, for example, momentary overvoltage, surges, noise and momentary power outages enduring for a very short time period, must be tolerated.
Apparatus for storing data in a non-volatile memory during power outages is disclosed in Canadian Patent Application Serial No. 484,608 in the name of Germer, 25 filed June 20, 1985.
Testing of an electronic demand register may conveniently be performed by interrupting the normal processing ~eing done by an electronic demand register and inserting test data into the volatile memory elements. In order to avoid losing billing data and certain programmed constants while the volatile memory elements are used for test operation, such items are also stored in non-volatile memory in a manner generally analogous to -the technique used for storing them in -the eVen-t of a power outage. Apparatus for storing data in a non-volatile memory during test ~3~
~ ME-137 operation is disclosed in Canadi.an Application Serial No. 484,607 to Germer, filed June 20, 1985.
The volatile memory and non-volatile memory may require incompatible data formats. That is, a microproce~sor containing the volatile memory may be restricted to producing blocks of output which have -too many, or too Eew, bits for reception by the volatile memory and vice versa. Without a technique for translating -the la:nguage of each of these devices into the language of the other, they are incapable of communicating with each other.
O'BJECTS AND 'SUMMAR~' OF' T~IE 'INVENTI'ON
~ ccordingly, it is an object of the invention to provide an electronic demand regis-ter having a memory interface which permits communication between a non-volatile memory and a volatile memory.
it is a further object of the invention to provide an electronic demand register in which a communications buffer assembles a data package for transmission to the non-volatile memory which because of the manner in which the non-volatile memory recognizes and stores data, forces compatability between the data formats.
It is a further object of the invention to provide an electronic demand register in which a communications buffer shifts and discards data serially received from the non-volatile memory to plaee the data in a format whieh is aeeeptable Eor communication to the volatile memory.
Briefly stated, the present invention provides an electronic demand register for an electric meter which includes a volatile storage for normal processing of data and a non-volatile storage into which data is seriall~ written upon the occurrence of conditions which may threaten the integrity of such data and from which the data is again retrieved when ,.. ~
,,; ,~.i ~.~33~
ll-M~-137 the condition no longer existsO ~le data Eormats for transmission of tlle data to the non-volatile Memory and for receiving it -therefrom clo not agree with -the data formats which the vola-tile storage must have. A
communications buffer assembles a data package for -transmission to the non-volatile memory which has a format which can be suitably serially transmitted to the non-volatile memory and be properly interpreted there due to the manner in which the non-vo:Latile memory recogni~es and stores data. In addition, the communications bufEer receives the serial data from the non-volatile memory and, by left shift and selection of only valid portions of the data, assembles data suitable for transmission to the volatile memory.
According to an embodiment of the invention, there is provided apparatus for communicating between a first memory capable of sending and receiving first data words having a first number of bits and a second memory capable of sending and receiving second data words having a second number of bits wherein neither of the first or the second numbers oE bits is evenly divisible by -the other thereof, comprising means for assembliny a first predetermined number of -the first data words into a first data block, means for appending a leading word to the first data block, means for serially transmitting the leading word and the first data block to the second memory, the leacling word inclucling a pattern of bits which are at leas-t partly ignored by the second memory and a remainder of the leadin~ word, together with the Eirst data block, forming the second clata word whereby -the second memory is effective to receive data from the first memory, means Eor serially receiving a second prede-terminecl number of the second words from the second memory, means for forming the second predetermined number of ~35~6 11-~E-137 the second words into a second data block, means for performing one of a shift and a selective transfer on the second prede-termined number of the second words whereby the second words in the second da-ta block are converted to a third da-ta block, the -third data block being a third predetermined number of the first data words and means :Eor communicating the third clata block to the first memory.
Accor(lirly to a fea-ture o:E the inventlon, there is provicled a method for communicatirlg between a first memory capable of sending and receiving first data words having a first number of bits ancl a seconcl memory capable of sending and receiving second data words having a second number of bits wherein neither of the first or the second numbers of bits is evenly divisible by the other thereof, comprising assembling a first predetermined number o-f the first data words into a first data block, appending a leading word -to the first data block, serially transmitting the leading word and the first data block to the second memory, the leading word including a pattern of bits which are at least partly ignored by the second memory and a remainder of the leading word, together with the first data block, forming the second data word whereby the second memory is effective to reeeive data from - the first memory, serially receiving a second predeterminecd number of the second words from the second memory, forming the second predetermineclrlumber of the seconcl words into a seconcl data block, 3~ per:Eorming one of a shift ancl a seleet:ive transfer on the seeoncl prec1etermined number of the seeond words whereby -the seeond words in the second data block are converted to a thircl data blocX, -the third data block bein~ a third prede-termined number of the first data words and comrnunicating the third data block to the first memory.

~L2;~3~6 ll-ME-137 The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction wi-th the accompanying drawings, in which like refer~nce numerals designate the same elements.
BRIEE' DESCRIPTION OF THE DRAWINGS
~ i'ig. 1 is a schematic diagram of an electric me-ter to which the present inven-tion may be applied~
Fig. 2 .is a block diagram of a demand register of Fig. 1 according to an embodim0nt of the invention.
E'ig. 3 is a simplified block diagram to which reference will be made in describing the manner in which da-ta is formatted for transmission to, and after reception from, the non-volatile memory of Fig. 2.
Fig. ~ is a chart showiny the format of data transmitted to the non-volatile memory.
Fig. 5 is a chart showing the format of data received from the non-volatile memory.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENrr Although the present invention may be adapted to any sui-table style of electric meter which employs an element rotating at a speed proportional to power consumption, including single phase meters wi-th one or more current windings and polyphase meters, for concreteness, -the detailed description which follows is directecl toward an illustrative example of a 2-w:ire single phase meter of the -type having a single current coil and a single voltage coil.
Referring now to Fig. 1, there is shown, generally at 10, an electric meter which includes a small induction motor 12 driving a reyister 1~.
Induction mo-tor 12 inclu~es a stator 16 macle up of a vol-tage coil 18 and a current coil 20 disposed on opposite sides of a disk 22. Voltage coil 18 employs ~23~S~
ll-M~-137 a core 24 upon which is wound a larye number of turns of fine wire. Voltage coil 18 is connected across lines 26 and 28 which feed power to a load (not shown). Current coil 20 employs a core 30 upon which a small nllmber of turns, typically one or two, of heavy conductor are wound. Current coil 20 is connected in series with the power beiny fed to the load on line 26.
Disk 22 is affixed to a shaft 32 which is suppor-ted on suitable bearings (not shown) to permit concerted rotation of disk 22 and sha-ft 32 under the influence of a rotating mayne-tic field produced by the combined influence of voltage coil 18 and current coil 20. A permanent magnet 3~, having its poles disposed on opposite sides of disk 22, applies a retarding force which is proportional to the rotational speed of disk 22. The rotational torque produced by voltage coil 18 and current coil 20 combined with the retarding torque produced by permanent magnet 34 is effective to rotate disk 22 at a speed which is proportional to the product of the voltage and the current; that is, the power consumed by the load.
Register 1~ includes a watthour register 36 which may include, -for example, a plurality of dials 38 which are suitably gearecl and driven by a suitable mechanical coupling ~0 in propor-tion to the rotation of shaft 32. In the embodiment shown, mechanical coupling ~0 includes a worm ~2, which may be integrally formed in shaft 32, which engages and rotates a worm gear ~. Additional eLemen-ts may be present in mechanical coupling ~0 for coupling -the rotation o worm gear ~ to watthour register 36 with or without change in speed and direc-tion according -to the design of the particular electric meter 10. As is conventional, watthour register 36 totals the number ~L~3~
ll-ME-137 g o~ revolu-tions of shaft 32, sui-tably scaled by the gear ratios employed, ~or billing purposes.
A demand register 46, shown schematically as a box in Fig. 1, is also connected by a suitable coupling means ~8 to respond to the rota-tion of shaft 32. In the pr.ior art, demand register 46 is conventionally a mechanical regis-ter having dials, or other indicating devices (not shown), and coupling means ~ ; conventionally a mechanicrll arrangement including shafts ancl geariny driven by rota-tion of shaft 32. rlrhe dials or indicating devices in the mechanical embodiment of demand register 46 are urged forward for a fixed period of time by a pusher mechanism (not shown). The pusher mechanism is reset and restarted at the end of each of the fixed periods of -time, leaving the indica-ting devices with an indication proportional to the power usage (the demand) during the fixed period of time. rrhe indication on the indicating devices at any time is, therefore, the highest demand which has occurred duriny any of the time periods since the last time the indicating devices were reset. rrhe recorded demand is employed in billiny. In the present invention, demand reyister ~6 is an electronic demand register.
Referring now to Fiy. 2, there is shown, a simplified block diagram of a demand register 46 according to an embodiment of the invention. For present purposes, it is sufficient to note that the signal related -to power usage fed from coupliny means 4~ to demand register 46 is an electronic siynal haviny a characteristic such as, for example, a frequency, which is variable in dependence on the rate of power usaye. Any suitable electronic signal generating apparatus, such as disclosed in the referenced prior patents, may be employed to produce a power usage signal which is applied on a line 50 to a 3~3~
ll-M~-137 processor 52 in demand register 46. Processor 52 appropriately performs calculations on -the usage data -to derive desired demand parameters and stores the result. In addition, processor 52 may provide an output on a line 54 suitable for driviny a display 56.
In addition, the stored data may be transmit-ted 011 a line 5~ to a remote location (not shown) for ~urther analysis and/or billing.
~ue to the extremes of environment in which electric meters may be used, display 56 may neecl special compensation ~or environmen-tal parameters.
Such special compenstion may include a display temperature compensator 60 whose detailed s-tructure and ~unction are not o-f interest to the present disclosure.
As previously noted, processor 52 conventionally employs volatile random access memory elements which lose any data stored in them in the event of a power outage. This is usually not acc~ptable in an electric meter where such loss of usage and/or demand data has a negative ~inancial impact on the utility supplying the electric power.
Non-volatile storage elements such as, ~or example, electronically erasable programmable read only memory elements, are well known -for use with processor 52.
However, such non-volatile storage elements normally employ serial reading and writing. This provides relatively slow memory access -times on the order of 10 or 20 milliseconds. This is too slow for most applications. In addition to -this drawback, the power required to write such memory elements is quite high compared to that required by volatile memory elements of processor 52. E'inally, a wear-ou-t mecharlism in electronically erasable programmable read only memory cells limits the number o~ times they can be erased and re-recorded. About 10,000 cycles of write and ~L~3~
ll-ME-137 erase brings such a memory element to the end of its reliable useful life. Memory elements in processor 52 must, oE course, be written and erased many thousands of times a day. Thus, an electronically erasable programmahle read only memory would have a very short li~e as the opera-ting memory for processor 5~. In its role in non-volatile memory 6~, however, electronically erasable programmable read only memory elements are erased and rewritten only when a relatively serious power outage occurs and possibly during a relatively small number oE tes-t cycles. Such operations are not expected to occur on a frequent enough basis in the register of an electric meter to represent a limit on the life of the register.
In order to provide saEe storage for data and/or programmed constants during a power outage or a test operation, a conventional non-volatile memory 6 is provided into which such data and constants can be written in the event of a power outage and from which the data and constants can be again read upon restora-tion OL normal conditions.
rrhe data which processor 52 transmits for display and/or ~he manner in which processor 52 opera-tes on the input data to produce internally stored values may be modiEied according to a manual input 62. For example, manual input 62 may contain means (not shown) Eor placing demand regis-ter ~6 into a test mode in which the volatile memory elements in processor 52 receive and process test data rather than normal usage data. Prior to permi-tting the replacement oE normal operating da-ta with test data, the normal operating data and programmed constants are transmitted Eor storage in non-volatile memory 64 until the resLImption of normal operation. The content oE manual input 62 and the manner in which processor 52 and non-volatile memory 6~ cooperate to store data in 3~
ll-ME-137 non-volatile memory 6~ prior to a test operation and to retrieve it at the end of a test operation i5 detai:Led in the re~erenced patent application.
A power supply and power rnonitor 66 receives AC power f;om lines 26 and 2~3 for the production of a regulated DC voltage which is applied on a line 6~ to all circuits in demand register ~6 requiring such power. In addition to producin~ re~ulated ~C power, power suppi.~ and power monitor 66 also monitors the condition of the AC power on lines 26 and 2~ and, in response to certain detected conditions, applies control signals on a line 70 to processor 52 which controls the transfer o~ data from processor 52 to non-volatile memory 6~ in the event of an apparent power outage and resets processor 52 in the event of an actual power outage. r~e detailed structure and operation of power supply and power monitor 66 is contained in the re-ferenced patent application.
Problems may be encountered in passing data back and forth between processor 52 and non-volatile memory 6~ due to the possibility oE different and incompatible data and/or instruction formats of commercially available apparatus. In one embodimen-t of the invention, data is stored in processor 52, which may be a microprocessor such as, for example, a type NEC 7500 microprocessor, in four-bit nybbles bu-t is only transmitted and received by processor 52 in ~-bit serial words which cannot be interrupted once transmission has begun. In this embodiment, non-volatile memory 6~, which may be, :Eor example, an Nr~C9306 non-vola-tile memory, requires either 9 bi-ts of instruction to read or erase a 16-bit data word from non-volatile memory 6~ or 25 bits oE ins-truction to write a 16-bit word contained in the instruction in non-volatile memory 6~. Neither of these requirements is evenly divisible by eight as re~uired by the ou-tput ~33~6 ll-ME-137 format of processor 52. In addition, when non-volatile memory 64 transmits a block of data, the block contains a leading zero followed by 16 data bits for a total of 17 bits i.e. also not divisible by eicJht.
Referring now to E'ig. 3, a main memory 72 of processor 52 transmits and receives data only in paralle:L in four-bit nybb:Les as indicated by broad arrows 7~ which communicate to and from a communications buffer 76. Communications buffer 76 is employed to assemble a data package received from main memory 72 in suitable form for transmission to non-volatile memory 64 or for assembling a data package received from non-volatile memory 64 in suitable form for -transmission to main memory 72.
A serial input/output interface 78 sends and receives data only in eight-bit words. That is, for -transmitting data to non-volatile memory 64, serial input/output interface 78 receives two of the four-bit nybbles from communications buffer 76. Immediately that the required eight bits are received in serial input/output interface 78, serial input/output interface 78 automatically begins serial transmission of the data to non-volatile memory 64. Once serial -transmission has been started, it canno-t be s-topped until the entire eigh-t-bit word has been -transmitted.
When receiving serial data from non-volatile memory 64, as soon as eight data bits are received and stored in serial inpu-t/output interface 7~, the resu:Lting eight-bit data word is transferred in parallel from serial input/out in-terface 78 -to two four-bit storage locations in communications buffer 76. rL'he problem, then, is to find a way for serial input/output interface 78 to send and receive aight-bit serial data when non-volatile memory 64 requires input data and produces output data in formats which are not evenly ~35~L~3 ll-M~-137 divisible by eigh-t.
Advantage is -ta]cen of certain characteristics of non volatile memory 64 to permit com~unica~ions buf~er 76 -to manage -the transmission and reception of data with incompa-tible formats.
Non-volatile memory 64 ignores leading seros in a received word and i5 enabled to beyin receiving data when it receives a one. Following the leading one, non-volatile memory 64 recIuires a four-bi-t operatiny code to tell it whether to read, erase or write, followed by an address where -the operation is -to take place. In the case of a write operation, the address is followed by a 16-bit data word. That is, except for a write operation, the data transmission required includes nine bits~ A write operation recluires 25 da-ta bits. In addition, during a read operation, the first serial bit read out from non-volatile memory 64 is always a zero followed by 16 data bits.
In preparation -for transmittiny data to non-volatile memory 64, communications buffer 76 assembles either two eight-bit words for erase or read or -four eight bit words for write (re-fer to Fig. 4).
The first seven bits in the first eight-bit data word are zero and the eighth bit is a one. The next eight-bit word includes the four-bit operation code and the four-bi-t address. Since non-volatile memory 64 ignores leading zeros, the first seven bits in the first word are ignored. Non-volatile memory 6~ then recognizes -the one in the eighth position in the first eight~bit data word and is thereby enabled to properly receive the succeeding eight bi-ts in the seconcl data word for a total of nine bits received. In a write operation, the second eight-bit word is followed by an additional two eight-bit data words containing the sixteen bits of data.
In order to accomoda-te data read out from ~L~33~
ll-ME-137 non-volatile memory 64 which, as noted above, contains a leading zero followed by 16 data bits, the fi.rst eight ~its (a zero followed by seven data bits is stored in communications buffer 76 as the first received word (see Fig. 5). The next eight bits, all of which are data bits, are stored as the second data word. One additional data bit is received. 'I~lis one additional data bit is posit:ioned as the first bit in a third eiyht-bit data word. '['he state of the last seven bits in the third eigh-t-bit data word i8 a matter of indifference. The three data words are then shifted one bit lef-t in communications buffer 76.
This shifts the leading zero out of the first eight-bit data word, effectively erasiny it, and shifts the leading bit in the second and third eight-bit data words into the last position in the first and second eight-bit data words respectively.
Upon completeion of the left shift, the first and second data words contain all 16 data bits which are transmitted to main memory 72 four bits at a time.
: The third data word contains garbage which is discarded by failing to transmit it to main memory 72.
Having described preferred embodiments of the invention with reference to the accompanying drawings, i-t is to be understood that the inven-tion is not limited to those precise embodiments, and that various changes and modifications may be effected therein hy one skilled in the art without departing frorn-the scope or spirit of the invention as def:ined in the appended claims.

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. Apparatus for communicating between a first memory capable of sending and receiving first data words having a first number of bits and a second memory capable of sending and receiving second data words having a second number of bits wherein neither of said first or second numbers of bits is evenly divisible by the other thereof, comprising:
means for assembling a first predetermined number of said first data words into a first data block;
means for appending a leading word to said first data block;
means for serially transmitting said leading word and said first data block to said second memory;
said leaing word including a pattern of bits which are at least partly ignored by said second memory and a remainder of said leading word, together with said first data block, forming said second data word whereby said second memory is effective to receive data from said first memory;
memory for serially receiving a second predetermined number of said second words from said second memory;
means for forming said second predetermined number of said second words into a second data block;
means for performing one of a shift and a selective transfer on said second predetermined number of said second words whereby said second words in said second data block are converted to a third data block, said third data block being a third predetermined number of said first data words; and means for communicating said third data block to said first memory.

2. A method for communicating between a first memory capable of sending and receiving first data words having a first number of bits and a second memory capable of sending and receiving second data words having a second number of bits wherein neither of said first or second numbers of bits is evenly divisible by the other thereof, comprising:
assembling a first predetermined number of said first data words into a first data block;
appending a leading word to said first data block;
serially transmitting said leading word and said first data block to said second memory;
said leading word including a pattern of bits which are at least partly ignored by said second memory and a remainder of said leading word, together with said first data block, forming said second data word whereby said second memory is effective to receive data from said first memory;
serially receiving a second predetermined number of said second words from said second memory;
forming said second predetermined number of said second words into a second data block;
performing one of a shift and a selective transfer on said second predetermined number of said second words whereby said second words in said second data block are converted to a third data block, said third data block being a third predetermined number of daid first data words; and communicating said third data block to said first memory.
3. A data communications system comprising:
a communications buffer;
a serial input/output interface;
said communications buffer including means for communicating data to and from a main memory and

Claim 3 continued:
for communicating said data to and from said serial input/output interface;
said serial input/output interface including means for serially communicating fixed-length data words to a non-volatile memory and for serially receiving data words from said non-volatile memory;
said non-volatile memory being of a type which requires an input data format and an output data format which includes a number of bits which is not evenly divisible into or by a number of bits in said fixed-length data words;
said communications buffer including means for forming a data package for transmission through said serial input/output interface to said non-volatile memory, said data package including a leading data word appended to said data from said main memory, said leading data word including a first portion which is ignored by said non-volatile memory and a second portion which is recognized by said non-volatile memory, a combination of said second portion and said data forming said input data format compatible with said non-volatile memory;
said communications buffer including means for forming a second data block of data which has been serially received from said non-volatile memory; and said communications buffer further including means for performing at least one of a shift and a selective transfer on said second data block whereby said second data block is converted to a third data block having a format compatible with said main memory.