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BACKGROUND OF THE INVENTION
This invention relates generally to the field of duplex communications, and
more particularly to systems wherein a master unit transmits to and
receives from a multiplicity of subsidiary units over a single channel.
There are many types of systems wherein one master unit communicates with a
number of subsidiary units utilizing a two-way flow of data over a single
communication channel. There are paging systems using RF transmission
wherein each unit has an assigned address and the master unit transmits a
given address, encoded in some fashion such as a sequence of tones
modulated onto a carrier as exemplified in U.S. Pat. No. 3,766,523, or as
digital "words" in a bit stream as in in U.S. Pat. No. 3,855,576, both
patents being assigned to the same assignee as is the present invention.
The latter patent will be referred to again hereinbelow. In the former
patent, the pager unit having the assigned address decodes it upon
reception and in one of a number of ways alerts the pager user that he has
been paged.
Another application requiring a two-way flow of data involves a large
computer, a control unit and multiple satellite CRT terminals, all
inter-connected by cables. Such a system might be used as on a production
line where the assembled products; e.g., automobiles, may require special
components for certain units going down the line. Information relative to
each individual unit's requirements is stored in the master computer. An
operator along the line can query the computer via one of the CRT
terminals as to any special components. The computer, of course, will
reply almost instantaneously, but the operator must then return to the
production line, where the unit in question has been moving along. Such
systems typically poll each CRT terminal in sequence, wait for an answer,
and then move on at the end of the answer or after a set period such as
three seconds.
Another system, used as in inventory applications, utilizes detached
portable units including a data entry terminal and data storage means. The
user enters inventory data as he or she moves along the aisles of a
warehouse, by keyboard and/or light pen. Then, at the end of a given time
period, perhaps several hours, the portable unit is brought to a master
computer terminal and plugged in for transfer of the stored data into the
master computer. It is obvious that in the two latter systems, a detached
or completely portable two-way terminal in constant touch with the
computer would be preferred, with some means for controlling the flow of
data between the portable units and the master or host computer for
maximum channel efficiency.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a system for
two-way communication between a multiplicity of portable units and a
master computer.
It is a particular object to provide a system controller for interfacing
with all of the elements of the system and which provides maximum
efficiency in channel use.
These objects are partially achieved in a system described more fully in a
co-pending application, Ser. No. 967,805, filed as of even date with the
present invention. However, further increase in channel efficiency may be
achieved in the last referenced system or other similar system by a unique
arrangement for polling without time-wasting delays while waiting for
responses from the various units.
In the present polling system, each portable unit is assigned a unique
address code which has an assigned position in a queue of all the portable
address codes in the RAM memory of the controller unit. Attached to each
address code is a "tag" which indicates whether the portable unit is
"active" or "inactive", "active" meaning that the unit is presently
processing data or has been within a predetermined time period prior to
being polled. In any one polling sequence, the controller polls in
sequence each active unit, then polls a set number of inactive units. If
any portable unit responds (with the address code assigned to the
controller) within a time slot or window following reception of its own
address code the controller aborts the address code then being sent out
and sends out a comma or non-data bit signal. The controller also
identifies the received message as being from the unit which responded.
Following receipt of the message from that portable, the controller
continues the polling sequence, beginning with the address code which had
been aborted. Alternatively, following an interruption of the polling
sequence, the controller may send a short comma, then transmit to other
portable units any stored messages not requiring responses.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram showing a complete system which could utilize the
present invention.
FIG. 2 is a portion of the portable unit queue which is used in the
description of the operation of the system.
FIG. 3 is a diagram indicating a portion of the controller transmission
sequence.
FIG. 4 is an elaboration of one possible block of the chart of FIG. 3.
FIG. 5a is a different version of the elaboration of FIG. 4.
FIG. 5b is a chart of a possible response to the polling sequence.
FIG. 6 is an elaboration of a different block of the chart of FIG. 3.
FIG. 7 is a flowchart illustrating the operation of the controller unit in
polling for data from the various portable units.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 is an overall view of a total system which could utilize the polling
system of the present invention. A host or master computer 10 is coupled
by a link 11 to a control unit 12. The computer could be any one of a
number of relatively large computers, an example being the IBM 360/370
series. The link 11 could be a short DC data link or a leased telephone
line of almost any length with a modem at each end. Communication over
this link will be explained only to the extent necessary for an
understanding of the present polling system.
Many features of the control unit 12 are described more fully in the
co-pending application Ser. No. 967,805 filed as of even date with the
present invention and covering the entire system. However, all the
information necessary for undertanding and practicing the present
invention will be given herein.
The host computer 10 has the capacity to be coupled to as many as 32
control units 12 (one is shown). By means of a base station or FR
transmitter/receiver 13, each control unit 12 may be coupled to as many as
32 portable units 14 (five are shown in FIG. 1.)
The present polling system is described in terms of the coupling of one
control unit 12 and its portable units 14-1 to 14-n, where n is 32 in a
preferred embodiment although the invention is not so limited. Also, in
the preferred embodiment, the coupling is by way of a two-way radio link,
but the invention is not limited thereto either.
In the usual application, the host computer 10 will initiate polling and
receive responses in whatever protocol, language and baud rate it
requires; i.e. Binary Synchronous Landline, Extended Binary Coded Decimal
Interchange Code (EBCDIC) or American Standard Code for Information
Interchange (ASCII), at transfer rates from 1200 to 9600 bits per second.
The controller unit 12 will store all information received from the host
computer 10 and convert it to the proper language and speed required by
the portable units 14.
The control unit 12 then polls the portable units 14 in accordance with the
polling sequence as described hereinafter, processes all return
information and even, if desired, provides portable to portable
communication.
The key to the polling sequence is the queue discipline of the control unit
12 which in this case assigns to each portable unit 14 a position in the
queue which does not change; e.g., 14-1, 14-2, 14-3 etc. However, in
contrast to the prior art, where every unit was queried in turn, with a
pause as long as three seconds following each poll for possible response,
the controller 12 "tags" each control unit address code in the RAM memory
with an active or inactive status identification. These tags are
continually updated.
A partial listing of a typical queue is represented in FIG. 2, including
portable unit 14 address codes with status tags. This listing will be used
hereinafter in the further explanation of polling, but is of course
exemplary only. An "active" tag means that the respective portable unit is
presently processing received data, is generating data (via keyboard or
light pen), or has done so within a predetermined time period; e.g., 5
minutes. When no activity has occurred regarding a particular portable
unit during the 5 minute timing interval, the address code of that unit
is then tagged as "inactive".
FIG. 3 shows a portion of one particular polling sequence and including a
block 16 which includes the address codes of all active units, a block 18
which includes a given number (4 in the present embodiment) of address
codes of inactive units (the inactive units chosen will be discussed
hereinbelow). Following the blocks 16 and 18 is a block 20 during which
any stored data not requiring a response is sent out by the control unit
12. This block will also be discussed further hereinbelow. Then another
polling sequence begins with another block 16. The diagram of FIG. 3
assumes that no units respond to the polling for data and that therefore
there are not interruptions to the sequence.
It is to be noted here that, in the present embodiment, all portable units
14 have the same first address code word, and each word comprises 46
binary bits, but these limitations are not necessary for the present
invention.
In FIG. 4 the beginning portion of block 16 is shown with the address code
A.sub.1 B.sub.1 for portable unit 14-1, followed by a comma is a 22. A
comma transmission period of non-data signal which serves to separate
various data signals, and in this example is a series of 17 1/0 bits at
about 1200 Hz. The data transmission between control unit 12 and the
portable unit 14 is, in the present instance, ASCII code at a rate of 1200
Baud. Following the first comma 22 is address code A.sub.1 B.sub.2,
another comma 22, address code A.sub.1 B.sub.3, another comma 22, etc.
Given the queue shown in FIG. 2, this sequence would continue with A.sub.1
B.sub.6, comma 22, A.sub.1 B.sub.9, and including all "actives" in the
queue.
Since it will be assumed, in connection with FIG. 5, that portable unit
14-2 will have a resonse ready when polled, a window 24 has been indicated
during which portable unit 14-2 must respond with the address code of the
terminal. The window 24 ends well before the end of address code A.sub.1
B.sub.3, allowing a safety margin in which a control unit 12 can interrupt
the polling sequence before A.sub.1 B.sub.3 is completely transmitted.
When the address code A.sub.1 B.sub.3 transmission is aborted, the control
unit tags this address as the starting address of the next polling
sequence. The control unit 12, upon recognizing its address code will
begin transmitting a comma 26 of at least 48 bits, and thereafter any
stored surplus base messages, otherwise comma will continue until the end
of the transmission from portable unit 14-2 or a predetermined portion
thereof as will be discussed hereinafter. This simultaneous transmission
further increases channel utilization.
FIG. 5A shows the beginning portion of block 16' which is how block 16
would appear if portable unit 14-2 responds during the window 24. Here the
sequence includes A.sub.1 B.sub.1, comma 22, A.sub.1 B.sub.2, comma 22,
A.sub.1, comma 26, and, possibly, data (not shown).
FIG. 5B shows the response which the portable unit 14-2 must make during
window 24 (automatically, of course, since the window may be of the order
of 75 milliseconds). The response will include a comma 28, A.sub.b B.sub.b
(the control unit 12 address code) and a 1-bit comma 30. It should be
noted that many variations of address codes/comma formats are possible
within the scope of the invention in addition to the ones embodies here.
Following the reception by the control unit 12 of the message or message
portion from portable unit 14-2, the polling sequence will resume with
address code A.sub.1 B.sub.3 for portable unit 14-3 and continue as
before.
FIG. 6 in an expansion of the block 18 of FIG. 3 and is also based on the
queue discipline of FIG. 2. Thus, following the polling of all active
units, a given number (in this instance, 4) of the inactive units is
polled. It is here assumed that the last inactive unit polled in a
previous sequence was the last inactive unit in the complete queue.
Therefore, the polling sequence of block 18 is now A.sub.1 B.sub.4, comma
22, A.sub.1 B.sub.5, comma 22, A.sub.1 B.sub.7, comma 22, A.sub.1 B.sub.8,
comma 22, unless one of these four portable units responds. In that case,
the sequence is interrupted as before, then continued with the aborted
address code. Following the sequence of block 18, block 20 follows with
whatever surplus messages have been received and stored in the control
unit 12. These are messages which do not require an immediate response
from the portable unit involved.
Another polling sequence begins after block 18, or after block 20 if a
block 20 is sent. If there had been no responses from any portable unit
during the previous polling sequence, the next block 16 would begin with
address code A.sub.1 B.sub.1 unless portable unit 14-1 had by then been
inactive for more than the 5 minute limit. In that case the first address
code in block 16 would be A.sub.1 B.sub.2 since it is an active unit.
In the description of FIG. 3 hereinabove, a mention was made that possibly
only a portion of the A.sub.1 B.sub.2 message might be transmitted. This
would be the case if portable unit 14-2 was attempting to send a
relatively long message. Each transmitted block of data, following the
control unit address code, is limited to a predetermined number of bytes
and if the message to be sent requires a larger number of bytes, the flow
of data is cut off at the predetermined number and a signal is sent to
signify that more data of the same message will be transmitted on the next
sequence. A message number is included to avoid operating on the same
message twice. A block check number is also included for a determination
of accurate reception of the message.
During the next polling sequence portable unit 14-2 would again respond to
its address code and interrupt the sequence with the control unit address
and the second block of message data. If the message is concluded in the
second block, a signal to that effect is transmitted to the control unit
12. If still more data remains in the portable unit 14-2 memory from the
same message, the process will continue for a predetermined number of
polling sequences, preferably four. Then, if the message includes more
than four blocks of data, the control unit 12 assumes that there has been
an error, wipes out all record of the message from the control unit
memory, tags that portable unit "inactive" and polls for data again from
that same portable unit during a subsequent "inactive" polling sequence.
The flow chart of FIG. 7 shows the sequence of steps in the polling for
data sequence from control unit to portable unit. Polling is an invitation
from the control unit to the portable unit to send data to the control
unit, usually to be sent to the host computer. The first block "poll for
data" indicates that the control unit is polling all portable data
terminals in the sequence as described above. If no response is received
to a particular address code, that code will be included in the next
polling sequence unless, as described above, it is tagged "inactive"
before the beginning of that sequence. If a response is received from a
portable unit, the control unit determines whether this is a beginning of
a new message or a continuation of a message begun on a previous polling
sequence. If it is the beginning of a new message the control unit checks
the message number and the block check number to be sure that the message
has been received correctly. If not, the message is deleted from memory
and the particular portable unit is tagged "inactive" and polled for data
in the "inactive" polling sequence. If the message number and block check
number are satisfactory the portable unit is so notified (ACK) on the next
polling sequence. If the signal indicating that more data is waiting was
detected, the message block is stored and labelled and the unit is polled
for data on the next polling sequence. If a signal had been received
indicating that the message was complete, the control unit would transmit
the data to the host computer and while waiting for reply would not again
poll that particular portable unit. Returning to the point in the chart
where it was determined whether the message received was the beginning of
a new message or a continuation of a previously begun message, and if the
latter were the case, the next step in the control unit is to determine
whether four such blocks of the same message had been received. If the
answer is "no" the blocks are linked together in the control unit memory
and the message number and block check characters examined as before and
if the answer here is "yes" or "no" the same procedures apply as before.
However, if four blocks have been received without the signal indicating
that the complete signal has now been transmitted, the message is assumed
to be in error and it is deleted from the control unit memory and that
portable unit is polled for data on the next "inactive" polling sequence.
Thus there has been described and shown a system in accordance with the
present invention wherein substantial improvement in channel efficiency is
made in the two-way transmission of data between a control unit and a
multiplicity of portable units. Part of the improvement derives from the
fact that all so-called "inactive" units are not polled on each sequence,
and part by the fact that no delays are required in order to listen for an
answer since the system can abort the polling sequence at any point when
the control unit address is received, switch to transmission of surplus
base messages, and resume transmission of the polling sequence at the
address code which was aborted. Safeguards are also included for
preventing overly long messages which would typically be messages
containing a serious transmission error, so that the system or even one
portable unit is not blocked from further communication. The reader is
also reminded that the embodiment shown is only one of many possible
applications of the invention and that all applications, variations and
modifications covered by the appended claims are included.
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