JPH01176135A - Method and system for connecting automatic backup primary terminals to secondary terminals group - Google Patents

Abstract

PURPOSE: To carry on the data service despite of the down of a primary terminal unit by using one of both terminals as the next primary supplier of a service function by making use of the omission of a polling signal sent from the current primary supplier. CONSTITUTION: If it's supposed that a primary terminal 12 becomes inactive, a backup primary terminal 14 is connected to a cable 16. Thus, the terminal 14 automatically serves as an active or a primary supplier of services to the secondary terminals S2 to S6 due to the inactive terminal 12. However, the terminals S2 to S6 never know that the terminal 14 serves as the terminal 12 for their services. In another starting mode, the terminal 14 can function as an active terminal and the terminal 12 can back up the terminal 14. As a result, the data service can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and system for automatically pack-up primary terminals to a group of secondary terminals.

[Background technology]

In retail, Universal Price Code (UPC)
UPC codes are increasingly being used to facilitate transactions at retail checkout counters. The UPC code is, for example, printed on the product's container. The customer places the item at the checkout counter, and an operator there transfers the item's UPC code to the counter's scanner. The scanner is connected to a secondary or retail terminal (such as a cash register) at the counter, which in turn is connected to a primary terminal that controls multiple retail terminals in the store. The UPC code scanned at the checkout counter contains an item identification number that is used by the primary terminal to derive the item's current price and other descriptions. The price and description are then transmitted to the retail terminal requesting the data for use in displaying it to the customer, printing at least a portion of it on the sales tape, recording it on the customer's bill, etc. It will be done. −
Generally, the price and description for the UPC code is stored on the data disk of the primary terminal to facilitate its modification;
Allow price lookup (PLU) operations to be performed.

[Problems to be Solved by the Invention] The problem with the above system is that when the primary terminal is down 9" or becomes inoperable, data service operations such as PLU operations are transferred to the secondary terminal. This means that the aircraft will no longer be able to receive the call.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and system for automatically picking up a primary terminal for a secondary terminal so as to continue data service to the secondary terminal. .

[Means for solving problems]

According to one aspect of the invention, a network is provided which a) provides a primary terminal and a backup terminal, and b) allows messages from all of the secondary terminals to be received simultaneously by the primary and backup terminals. c) a first timeout to determine whether the primary terminal or the backup terminal is the primary source of the data service capability; d) transmitting a polling signal from a primary terminal or a backup terminal, whichever is said primary supplier, via said network so that a secondary terminal can receive data services; and e) If the polling signal from the current supplier is missing less than two times, it will be used to automatically switch to the other of either the primary terminal or the backup terminal and the other will be connected to the service. The present invention provides a method for continuously providing data service functions to a plurality of secondary terminals, including the steps of enabling a next primary provider.

According to another aspect of the invention, first and second primary terminals having first and second memory means for storing and reading data, respectively; a plurality of secondary terminals; A circuit network that connects a secondary terminal to the first and second primary terminals so that messages sent from the secondary terminal can be simultaneously received by the first and second primary terminals. including
The first and second primary terminals have timeout means for generating a first timeout and a second timeout, and the first timeout determines which of the first and second primary terminals the the first terminal to determine whether it is an active primary provider of service capabilities for a plurality of secondary terminals and which of the first and second primary terminals is a backup provider of the service capabilities; a plurality of secondary terminals when one of the first and second primary terminals is the active primary terminal; polling means for issuing a polling signal to the network for supplying the service function, wherein the lack of a polling signal from the active primary source within the two timeouts is used by the backup source; indicates that the active primary terminal is inoperable and that the backup source may become the next active primary terminal; means for maintaining a log file for special data stored in both second memory means, wherein said bottom active primary terminal is connected to said first and second a continuous data service adapted to maintain a log of said special data for subsequent transfer to said first memory means when activated to store said special data in both said first memory means; Provide a system that provides

Further, in accordance with another aspect of the invention, secondary terminals may be configured to operate without having to know whether the primary terminals are "down" or whether they are being serviced by an alternate or backup terminal. We provide a system that can operate on ``10,000 lines.''

〔Example〕

FIG. 1 is a block diagram of a system 10 in which the method of the present invention may be used. For System 1, for example, the retail industry mentioned above is selected to use the present invention.

The system 10 (FIG. 1) is connected to a first or "active" primary terminal 12 via a network cable 16.
and a second or “backup #primary terminal”
S2゜S3, S4, S5 and S6 connected to 14
It includes multiple secondary terminals such as. Primary terminal 12
．． 14 provides data services to secondary terminals. In this embodiment, at least a secondary 7min (S2
゜S4. S6) each have a scanner 18, 20.22 connected thereto.

The secondary terminal S2 and its scanner 18 (FIG. 1) constitute what is referred to as a checkout counter surrounded by a dotted rectangle 24. Customer checkout counter 2
When the purchased item is released at 4, the operator or clerk moves it to the scanner 18 to read the tag 26 or UPC code on the item. The output of the scanner 18 connects to a secondary terminal S2, which is a retail terminal (eg, a cash register). Secondary terminal S2
is connected to the active primary terminal 12 via a cable 16, for example. Here, the primary terminal 12 provides a price lookup function for the secondary terminal S2 via the node disk 28 connected thereto. Price data and descriptions of UPC codes scanned by scanner 18 have traditionally been retrieved from hard disk 28 and returned to secondary terminal S2 for processing the data.

When a primary terminal, such as No. 12, becomes inoperable, as in conventional systems, the secondary terminals will not be able to receive PLU functionality if it is only one primary terminal. In addition to the active primary terminal 12, the system 10 of the present invention uses alternate or backup terminals 14 to provide secondary terminals 82--
Continuously provides data services to S6.

Before describing in detail how the system 10 of FIG. 1 operates, the components used therein will first be described.

Backup f primary terminal 14 is primary terminal 12
is essentially the same as At any given time, either terminal 12 or 14 is the active primary terminal, but as soon as the system 10 is set up, one of the two primary terminals 12.14 is the active or primary source for the secondary terminal. provide services;

Assume now that primary terminal 12 is initially configured to be the active primary terminal.

In this state, the secondary terminals 82 to S6 receive PLU data from the primary terminal 12 in this example. Also, 1
Assume that the next terminal 12 becomes "inoperable." Since the pack-up primary terminal 14 is connected to the cable 16, it means that the primary terminal 12 is inoperable (as described above) and the primary terminal 14 automatically connects said service to the secondary terminals 82-S6.
As far as the secondary terminals are concerned, they are not aware that the primary terminals 120 and 14 are serviced by the primary terminals 14.
It can also be seen that in alternative starting times, primary terminal 14 can operate as a passive terminal and primary terminal 12 can provide backup functionality. Therefore, either primary terminal 12 or 14 when "active" is considered the primary provider of service. Naturally, the types of services provided by the primary terminal 12.14 are different for different fields of application, but the principle of operation is essentially the same.

Furthermore, the description of each component in FIG. 1 will be continued.

Having explained that primary terminals 12 and 14 are essentially the same, the general description of the primary terminals is terminal 1.
Let's talk about 2.

Primary terminal 12 (FIG. 1) includes an automatic DLC (direct link control) driver 30 that includes hardware and software that connects primary terminal 12 to cable 16, which in this embodiment is a DLC circuit. This DLC circuit is a conventional direct link control circuit used by NCR Corporation of Dayton, Ohio. network cable 16
is a two-wire system originally used in six-in-house operations. The software for the DLC driver 30 is stored in the RAM (not shown) of the primary terminal 12, and the software automatically refreshes the data. maintained by a backup battery system to protect against data loss when the primary terminal is disconnected. have

Communications backup manager 32 is software stored in RAM and handles all communications to terminal 12 and system 10.

For example, if a failure occurs in either the primary terminal 12 or the hard disk 28 connected to it, the communications backup manager 32 will be aware of this and will notify the DLC driver 30 to take appropriate action. For example, if hard disk 28 fails, communications backup manager 32 informs DLC driver 30 that data cannot be written to the hard disk. As a result, primary terminal 12 ceases to function as a provider of services or an active terminal. The backup primary terminal 14 then takes over as the active primary terminal.

The hard disk 28 of FIG. 1 is shown schematically and includes a conventional hard disk controller board and a VAST
Hard disk drivers interfaced with backup manager 34 (not shown)
including. The term "VAST" is an abbreviation for variable access storage technology. The VAST backup manager 34 is software stored in the RAM of the terminal 34 and its function is to write data to the hard disk 28.

Some data within system 10 is shared between active primary terminals (such as 12) and backup primary terminals (such as 12).
4) to be pulled up to both hard disks. For example, if the hard disk 28 of the active primary terminal 12 becomes inoperable, the VAST backup manager 34 will set a flag so that the data requiring backup is not stored on the hard disk.
Displays that the disk 28 cannot be written to. The VAST backup manager 34 then informs the communications backup manager 32 of the hard disk failure and begins the process of making the backup primary terminal 14 the active primary terminal. on the other hand,
The data that requires backup is the primary terminal 12.
was active, it was received by the backup primary terminal 14 at the same time as it was received by the primary terminal 12. This data is written to hard disk 28-1 connected to primary terminal 14.

VAST backup manager 34-1 then begins storing its data in log file 36-1, which is part of hard disk 28-1 associated with currently active primary terminal 14. Primary terminal 1
4 is active and the next data required to be backed up occurs and the hard disk 28 of the current backup primary terminal 12 becomes inoperable in the example currently being described, the current active primary terminal 14's VAST backup manager 34-1 continues to write data to primary terminal 14's log file 36-1. Thereafter, when the hard disk 28 of the current backup primary terminal 12 is repaired, the first action performed by the vAST backup manager 34-1 is to log the
The purpose is to send the data temporarily written to the file 36-1 to the VAST backup manager 34 for writing to the hard disk 28. In this example, if disk 28 of primary terminal 12 is inoperable for, say, 30 minutes, the data that was written to log file 36-1 during that time will be sent to hard disk 28 in just a few seconds. Ru. Eventually, the data is sent to the hard disk 28, and the VAST backup manager 34 of the current backup primary terminal 12 was previously set to begin storing the data requested to be backed up to the log file 36-1. Remove flag.

The primary terminal 12 then uses its hard disk 2
8 is now fully operational in this example and begins to function as a backup primary terminal.

The general function of circuit processor 38 (FIG. 1) is to handle the transmission of messages between DLC driver 30 and hard disk 28. The circuit processor 38 is 1
This is software written to the RAM of the next terminal 12. The circuit processor 38 is a record of which data was received from which terminal. For example, if a data message from secondary terminal S2 is to be written to hard disk 28 associated with terminal 12, circuit processor 38 maintains the path of the data message as coming from secondary terminal S2. After the data message has been written to hard disk 28, circuit processor 38 recognizes the secondary terminal as the terminal that should be notified that the data message has been written to hard disk 28. In this example, during the period when a data message (from terminal S2) is written to hard disk 28, primary terminal 12 checks whether there is a message to be sent to secondary terminal 83, 84, etc. poll. During this polling, circuit processor 38 tags received messages as coming from the corresponding secondary terminal.

CMOS memory (block 40) (FIG. 1) represents CMO8 type RAM used in system 10 to store important data such as cumulative totals. CMOS memory 40 has a built-in battery backup system that can maintain critical data for long periods of time (weeks to months).

User application 42 (FIG. 1) is system 1
Represents user application software for 0. Primary terminal 12 also includes a conventional processor, display, keyboard, etc. (not shown) to enable it to function as an intelligent terminal. The timer 44 is connected to the system 10 as described below.
indicates a hardware or software timer used for

As previously mentioned, backup primary terminal 14 is identical to primary terminal 12, except as described below. Therefore, each element of the backup primary terminal 14 has a value of "-1" to it.
Except for those marked with ``, the elements are the same as the corresponding elements of the primary terminal 12 and are numbered the same.For example, the automatic DLC driver of the terminal 14 is designated 30-1.

Having described how system 10 works and what components it includes, we now describe how automatic backup techniques and data flow are accomplished.

FIG. 2 represents a flow diagram illustrating the process of determining which primary terminal 12.14 should be the active primary terminal and which should be the backup primary terminal for system 10. During initial setup,
Timer 44 shared by one of the primary terminals 12° 14
．． 44-1, which has a short timeout built in. Now assume that primary terminal 12 has a short timeout. When the system 10 is first started, the operator first turns on the primary terminal 12. Thereafter, the primary terminal 14 is turned on. As soon as the primary terminal 12 powers up, its timer function or timeout occurs. Upon timeout, DLC driver 30 begins monitoring at its receiver and polls the signal on cable 16 as shown in step 46 of FIG. As shown in step 48, if no interwoven or polling signal is obtained within 275 m5 in this example, it means that the other primary terminal (terminal 14 in this case) is not active. Regular polling of system 10 occurs every 125-150 mS. In this example, since there is no interaf') or polling signal,
Primary terminal 12 becomes the active primary terminal of system 10 (step 50). In step 48, if the primary terminal 12 detects an interwoven or polling signal, it means that the terminal 14 becomes the active primary terminal, and therefore the primary terminal 12
would have become the backup primary terminal as shown in step 52. Even if the timer 44 of the primary terminal 12 has a short timeout, it is possible for the primary terminal 14 to become the active primary terminal. It occurs when primary terminal 14 is turned on before primary terminal 12 is turned on. Each of the primary terminals 12.14 has an initialization routine that can be switched to become the active primary terminal when it decides to do so, in accordance with the scheme described herein. When a primary terminal such as 12 is designated as the active primary terminal, its control is passed to a cooperating DLC driver and the secondary terminals 82 to 12 are designated as active primary terminals.
Start polling S6. During that period, primary terminal 14 is a pack-up primary terminal, which can be considered a secondary terminal in terms of having it perform functions similar to those performed by secondary terminals 82-S6, for example. It is a feature of the invention that it performs other functions while the pack-up primary terminal, such as 14, is idle in backup mode. For example, if a primary terminal (such as 14) had a scanner (such as 18), it would perform a similar function to a secondary terminal (such as 52).

In this example, primary terminal 12 (FIG. 1) continues to operate as the active primary terminal 12 of system 1o until a failure occurs therein.

The failure is evidenced by the absence of the 150 mS polling signal in this example.

During that period, primary terminal 12 is active;
DLC)' Raiha 30-1 in collaboration with backup terminal 14 sets timer 44-1 to 150 m5 and monitors circuit cable 16.

If the polling signal is received before the 150 mS timeout, the DLC dry nozzle 30-1 resets the timer 44-1 to set the next 150 mS period.

If the polling signal from the active primary terminal 12 is not received within the set period, the counter 4
4-1 timeout occurs. This timeout is used by the backup primary terminal 14 and the terminal 12 no longer works properly. Backup 1
Indicates that the next terminal 14 acts as the active primary terminal of the system 10. Primary terminal 14J''t: functions as an active primary terminal by starting to send a pooling signal to cable 16 via DLC driver 30-1.

Once started, primary terminal 12 becomes the source or active terminal servicing system 10, and primary terminal 14 is the backup terminal. Active primary terminal 12
polls all terminals in the system to see if they are active and running. backup·
Terminal 14 is also considered a secondary terminal since it performs functions similar to those of secondary terminals 82-S6 in addition to performing the functions of a normal primary terminal. As mentioned above, it is the primary terminal 12.
Activate the use of the backup terminal 14 instead of simply leaving it idle.

DLC driver 30 of active primary terminal 12 (
FIG. 1) first has a backup primary terminal 14 to be polled and an I-ring list of all terminals included in system 1o.

After that, the secondary terminals 82 to S6 in this next embodiment
is polled. The first step in the DLC protocol used is to send a ``Normal Response Mode Setup Message'' from the active primary terminal 12 to the backup terminal 14.
SNRM).

If the pack-up primary terminal 14 is operational,
It sends an unnumbered acknowledgment signal back to the primary terminal 12. Active primary terminal 12 then sends an acknowledgment response back to backup primary terminal 14. Polling of active primary terminals 12 proceeds similarly to secondary terminals 82-s6. For example, if one of the secondary terminals, such as s4, does not respond, it will generate a "no" response. In this situation, the active primary terminal 12 maintains a log file for 'bad' or inoperable terminals.

Once active primary terminal 12 determines that all other terminals in system 10 are active,
Start polling them for any messages they may have. If a secondary terminal, such as S4, wishes to send data to the active primary terminal 12, it will do so during its polling.

After the data is sent to the active primary terminal 12,
Terminal 12 receives an acknowledgment signal (A
CK) to the secondary terminal S4.

The secondary terminal S4 can then drop the data.

As previously mentioned, when data is to be backed up, it is stored on the hard disk 28 of the active primary terminal 12. That's Mata Nog Tsukup 1
It is also stored in the node disk 28-1 of the next terminal 14. Backup primary terminal 14 receives requests for data to be buffered via cable 16.

Assume now that the secondary terminal S2 is in a state where it has data to be backed up after being polled by the primary terminal 12. The secondary terminal S2 is active as shown in step 64 of FIG.
A formatted message is sent to the terminal 12 along with a request for the backlog f (B/lJ) and logical unit number (LUN). L
UN indicates the address of hard disk 28 in this example. However, LUN may also indicate a printer (not shown) associated with active terminal 12.

All messages from secondary terminal S2 are sent to the active primary terminal, which in this example is primary terminal 12. Backup terminal 14 also receives data at the same time, as shown in steps 64 and 66 of FIG.

As data is sent to the active primary terminal, the same data is stored in a buffer within the backup primary terminal 14. After receiving the data, the active primary terminal 12 performs a DL with the backup (B, /'U) primary terminal 14, as shown in step 68 of FIG.
Perform C verification. The B/lJ primary terminal 14 responds by sending an acknowledgment signal UI and a count (step 70). The count is a DLC that cooperates with the system 10 for use in maintaining transactional messages in transit.
used in protocols. This message count counts from O to 7 and back to O again. The active primary terminal 12 can know what message counts are associated with each secondary terminal as part of the known DLCf protocol.

After the B/lJ primary terminal 14 responds in step 70, the active primary terminal 12 communicates from the communications backup manager (CBUM) 32 to the VAST backup manager VBUM 34 as described above and as shown in step 72. Send that message. At the same time, the message to be buffered 7f is sent to CBUM32-
1 to VBUM 34-1 (of the primary terminal 14) (step 74). The message is then written to the hard disk 28 associated with the active primary terminal 12 (step 76). Similarly,
The message is also written to the hard disk 28-1 which is associated with the B,/'0 primary terminal 14 (step 78 in FIG. 3). Active primary terminal 12 then sends a response to the secondary terminal indicating that hard disk 28 has been updated (step 77 in FIG. 3).
). After that, VBUM of active primary terminal 12
34 is the message actually on the hard disk 28-1
Requests an update of the B/ll" primary terminal 14 as to whether the message has been written to the hard disk 28-1 (step 80). The VBUM 34-1 of the B10 primary terminal 14 indicates whether the message has been written to the hard disk 28-1. or respond by indicating that it has been backed up (step 82 in Figure 3, step 6 in Figure 4).
0). The active primary terminal 12 is shown in step 5 of Figure 4.
4 or go to point "C" and poll other terminals. B/TJ 1st Terminal 14 (7) VBt
If JM 34-1 indicates that the message was not written to hard disk 28-1 as desired, V
BUM 34 will maintain a log of this message in log file 36 (step 58 in Figure 4).

B/TJ primary terminal 14 will not accept updates to hard disk 28-1 until it is operational and data from log file 36 from terminal 12 is provided to hard disk 28-1 ( Step 62 in FIG. 4). Hard disk 28-1
When the fault is repaired, the messages in log file 36 are written to hard disk 28-1 in the manner described above. For messages that require backup, at the DLC level (step 68 in Figure 3)
Verification is performed at the second level (step 80 in FIG. 3), represented by the request for and VBUM 34.

A feature of this invention is that unless the active primary terminal (such as 12) writes the same data to the hard disk (such as 28), the B/1J primary terminal (such as 1
4) hard disk (such as 28-1)
This means that there is no writing for . This is 1 each
Next terminal 12°14 hard disk 28.28
-1 means that it can have the same data. This is especially important when writing important data such as inventory data or totals.

The next important feature is that the active primary terminal 1
In the event that B/'0 primary terminal 14 fails in the middle of processing, a secondary terminal (such as 32) can take over without knowing that the primary terminal has changed. If your data is backed up,
B/lJ primary terminal 14 (in this example) learns that primary terminal 12 is no longer operational;
Log file 36-1 through its VBUM 34-1
When the “down” primary terminal 12 becomes operational again, the current active primary terminal 14 will write the current B/TJ primary terminal 12's hard - Will pack up data in log file 36-1 to be backed up to disk.

[Brief explanation of the drawing]

Figure 1 is an overall block diagram of the system used to carry out the method of this invention, and Figure 2 shows how the system determines which of the primary terminals in Figure 1 is active or backup. FIG. 3 is a flowchart showing the operation sequence of a certain backup function, and FIG. 4 is a flowchart showing a certain operation of the system. In the figure, 10... A system using the method of this invention, 2
4...Checkout counter. Application agent Isao Saito

Claims (10)

[Claims] (1) Provide a primary terminal and a backup terminal, connect a secondary terminal to the primary and backup terminals via a circuit network, and transmit messages from either of the secondary terminals to the primary and backup terminals. simultaneously receiving a terminal, using a first timeout to determine whether the primary terminal or the backup terminal should be the primary source of the service functionality; emitting the polling signal through the network to enable the secondary terminal to receive the data service, whichever terminal is the primary source; A lack of a polling signal from a primary source can be used to automatically switch to the other of the primary terminal or the backup terminal, making the other terminal the next primary source for the service function. Multiple 2 including each process
How to continuously provide data service functions to the next terminal without permission. (2) The step of determining whether the primary terminal or the backup terminal at which the first timeout occurred
monitoring a polling signal of said network by one of the terminals, and if said polling signal is not received within said second timeout by said one of said primary or backup terminals at which said first timeout occurs; 2. The method of claim 1, including each step of feigning control as a next supplier. 3. The method of claim 1, wherein said step of providing includes the step of providing said primary terminal with said first timeout shorter than said backup terminal. (4) A method of continuously providing a data service function to multiple secondary terminals that backs up special data to be stored as one of the service functions, which comprises providing a primary terminal and a backup terminal, and providing a circuit network. connecting the primary and backup terminals to the secondary terminal via a determining whether the primary terminal or the backup terminal should be the primary source of the service function using a first timeout; transmitting a polling signal through the network to enable the secondary terminal to receive the data service even if one of the primary terminal or the backup terminal is the primary provider; If there is no polling signal from the current primary source within a timeout of , determining that the primary source is inoperable and automatically switching to the other of the primary terminal or the backup terminal; storing the special data in a log file of the next primary supplier of the service function, and storing the special data in a log file of the next primary supplier of the service function; a data service function comprising the steps of forwarding the special data of the log file to the primary source after being operational and capable of storing the special data on the primary terminal and the backup terminal; How to continue without permission. (5) The step of determining includes monitoring a polling signal of the network when the first timeout occurs at one of the primary or backup terminal; 5. The method of claim 4, including the steps of pretending to be the primary source if the polling signal is not received within the second timeout when one timeout occurs. 6. The method of claim 5, wherein the step of providing the terminal includes the step of providing the primary terminal with the first timeout shorter than the backup terminal. (7) first and second primary terminals, a plurality of secondary terminals, and connecting the secondary terminals to the first and second primary terminals, and transmitting messages from the secondary terminals to the secondary terminals. a circuit that enables simultaneous reception at a first and a second primary terminal, the first and second primary terminals having timeout means for generating a first and a second timeout, respectively; a timeout of 1 is used for the first and second primary terminals, which of the first and second primary terminals should be the active primary source of service functions for the plurality of secondary terminals; and determining which of the first and second primary terminals should be a backup source for the service function; Either one of the following terminals is the active 1
polling means for transmitting a polling signal to said circuit in connection with providing a service function to said plurality of secondary terminals when being a secondary source from said active primary source within said second timeout; The system wherein the lack of a polling signal is used by the backup source to indicate that the active primary terminal is inoperable and that the backup source may become the next active primary source. (8) first and second primary terminals including first and second memory means capable of writing and reading data, respectively; a plurality of secondary terminals; a circuit connected to a secondary terminal so that a message from the secondary terminal can be simultaneously received by the first and second primary terminals, each of the first and second primary terminals and a timeout means for generating a first timeout and a second timeout, the first timeout being used by the first and second primary terminals, and which of the first and second primary terminals determining which of the first and second primary terminals should be the active primary provider of service functions for a secondary terminal of the terminal, and which of the first and second primary terminals should be the backup source of the service functions; Each of the second primary terminals also provides the service functionality to the plurality of secondary terminals when one of the first and second primary terminals is the active primary provider. polling means for sending a polling signal to said circuit with respect to said active primary terminal, wherein the lack of a polling signal from said active primary source within said second timeout is used by said backup source to activate said active primary terminal. and the backup source may become the next active primary source, and the first and second primary terminals are connected to the first and second
means for maintaining a log file for special data to be stored in both of the memory means of the second active primary terminal, wherein said next active primary terminal maintains a log file of said special data to be later transferred to said first memory means. and storing said special data in both said first and second memory means when said first primary terminal becomes operational again. 9. The system of claim 8, wherein said secondary terminal is a retail terminal and said special data is a price lookup table and inventory data. (10) said first and second memory means having said log files associated with said first and second primary terminals being part of first and second hard disk files, respectively; 10. The system of claim 9 including first and second hard disk files.