Note: Descriptions are shown in the official language in which they were submitted.
~63~
MULTIPLEX SECURITY SYSTEM
USING REMOTE MICROPROCESSORS
BACKr,ROUND OF T~IE INVENTION
This invention relates generally to secu-
rity and environmental control systems and more
particularly to systems comprising multiple remote
stations or panels interconnected by multiplexed
communications with a master local station or panel
via a common communications line.
Several different kinds of multiplex secu-
rity systems have been previously employed. In
general, such systems include a plurality of remote
detectors who e outputs are connected over a common
transmission line to a central receiver. The cen-
tral receiver sequentially monitors the outputs of
such detectors.
U.S. Patent No. 3,927,404 to Cooper dis-
closes a system in which remote detectors are
interrogated one a-t a time by a control panel in a
central receiver. An address pulse generator in
the control panel transmits an address code to the
remote monitors. Each monitor is provided with a
counter-decoder which is responsive to a dif~erent
address code. Upon interrogation, only the ad-
dressed monitor responds. Multiple local control
panels can be interconnected and one of them oper-
ated as a central control facility controlling the
.. ~ ` '~
t7~i
other local panels and their respective remote
panel 5 .
This system has several principal draw-
backs. First, data transmission is only one
way--from the remote monitors to the control
panel. Operation of the remote monitors cannot be
altered by the central receiver. Second, polling
priorities among remote monitors are determined
solely by the control panel. Each remote detector
is polled and responds whether it has information
to send or not. Hence, considerable time can be
wasted before a remote detector with an important
message is polled. Third, the system requires
transmission of serial address pulses. If 256
remote monitors are in the system, 256 address
pulses must be sent and time provided for 255 moni-
tors to respond before the 256th monitor can
respond. Since the address generator operates at
51 Hz, this procedure requires 5 seconds--too slow
for many applications. This system also lacks
voice communications and means for selectively
passing either voice or data through the local
control panel to the central control facility over
a single telephone line.
U.S. Patent No. 3,828,313 to Schull, et
al. shows another form of security system. That
system comprises a central data processor connected
-- 2
, . .
to multiple remote receivers by a two-wire Gommuni-
cations line and a clock line. The cloGk line
provides for synchronous circuit operation. Two
different binary message wave forms are used--one
transrnitted only by the central panel, the other
transmitted by the remote panels~ No means for
prioritizing responses from remote terminals or for
enabling such a terminal to interrupt with an emer-
gency message are disclosed. It would be prefer-
able if a single message format could be usedthroughout the system. It would also be preferable
for the system to operate asynchronously.
Other security control systems are dis-
closed in U.S. Patent Nos. 3,792,469; 3,803,594;
3,936,821; 3,938,118; 4,019,172; 4,032,908,
4,056,684 and 4,067,008. Many of these systems
provide for multiplex communications between remote
security panels or alarms and a control panel.
However, none are known to provide asynchronous
two way communications in a ~ormat which permits
serial polling of the remote terminals but prior-
itizes their responses so that the most urgent
message is transmitted first. In addition, none
are known to provide a remote terminal with means
for signaling that it has an emergency message or
a local terminal with means for acknowledging suGh
a signal and thereby enabling the remote terminal
-- 3
to transmit its messaye. Also, none of the refer-
ences disclose combined two-way voice-data commu-
nications between a local terminal and a central
control facilitiy over a single telephone line.
Nor do they disclose means for transmitting voice
communications from the remote terminal throu~h the
local terminal to central via a telephone line
normally dedicated to data communications.
Accordingly, there remains a need for an
improved multiplex security control system having
these capabilities.
SUMMARY OF THE INVENTION
One object oE the invention is to provide
a multiplex security s~stem with high speed trans-
mission of important messages from remote panels to
the local panel.
A second object is to prioritize communi-
cations from remote panels so that panels with more
important messages can transmit before panels with
less important messages,
Another object is to maximize the amount
o~ communications time available for remote panels
to transmit information to the local panel.
A further object is to reduce the amount
of unused communications time in the system.
Yet another object is to increase the
numbers of remote panels that can be interconnected
in a single system.
An additional object is to enable remote
panels with emergency messages to interrupt routine
polling of remote panels.
A still Eurther object is to provide
two-way voice and data communications between a
local panel and its associated remote panels.
10A related object is to provide two-way
; voice and data communications from the local panels
to a central control unit via a single line.
In accordance with the foregoing objects,
one aspect of the invention provides the remote
panels with means for transmitting, in addition to
digital data, a request signal to the local panel
signifying that the remote panel has a message to
transmit. The local panel includes means for dis-
tinguishing the request signal from digital data
and for acknowledging the request. The acknowl-
edgement or grant message, or a first portion
thereof is superimposed over the request signal.
The remote panel includes means for sensing the
superimposed signal to turn off the request signal
so that the communications line is clear for the
transmission of the digital data.
- 5 -
In another aspect of the invention, the
remote panels, of which many can be connected to a
single local panel, include means for prioritizing
the order in which they transmit data to the local
panel. The remote panels assigned priorities, for
example, by setting different switch numbers in
each panel. The switch numbers correspond to
unique time slots in which each of the remote
panels can commence transmitting. Each panel
includes means for receiving any data on the com-
munications line. If another remote panel starts
transmitting during one of the earlier time slots,
the remaining panels, including the panel initiat-
ing the request signal, refrain from transmitting.
In one example, the highest priority
remote panel is assigned the first time slot and
the lowest remote panel switch number. The lowest
priority remote panel is assigned the last time
slot and the highest switch number. Following
receipt of a grant command from the local panel,
the remote panels begin counting time slots. None
of the panels can respond until the count equals
their respective switch number, and then only if
another panel has not already commenced transmit-
ting.
In a further aspect of the invention, the
local panel includes audio control means for
selectably transmitting either data or voice mes-
sages from remote panels to central. Either the
local panel or central can initiate data communica-
tions over an interconnecting telephone line. The
remote panel can also cause the local panel to
initiate such communications. Voice communications
can be initiated from the remote panel for example,
by setting a panic switch~ The local panel audio
control means then connects a speaker/microphone to
the telephone line to central and disables trans-
mission of data over such line. In another appli~
cation, a central station can "listen-in" at a
- remote location via the microphone of a remote
panel that has reported a burglar alarm to central
through the local panel.
The foregoing and other objects, features
and advantages of the invention will become more
apparent ~rom the following detailed description of
i~ a preferred embodiment of the invention, which
proceeds with reference to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a functional block diagram of a
multiplex security system according to the inven-
tion showing the three major subdivisions thereof.
Fig. 2 is a timing diagram showing an
example o~ data transmissions between the local and
remote panels of the system of Fig. 1.
' '
Fig. 3 is an expanded timing diagram of a
single loGal panel message of FigO 2.
Fig. 4 is a more detailed diagrarn of the
local and remote panels of Fig. 1 with the data
communications interface, the power supplies and
audio control element shown schematically.
Fig. 5 is an expanded portion of the tim-
ing diagram of Fig. 2 showing an example of opera-
~ tion of the communications protocol between the
-~ 10 local and remote panelsO
Fig~ 6 is a parallel flowchart of portions
of the programming of the microcomputers of the
local and remote panels of Fig. 1 to support the
communications protocol of Fig. 5, with dashed
arrows indicating interactions between the local
and remote panels.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
General System Descri~tion
Referring to Fig. 1, a multiplex security
system comprises three major subdivisions. The
first subdivision is a central control element 20,
referred to hereinafter as "central." Central
includes a conventional digital computer 22 and
modems 24, 24a, 24b driven by a real-time clock 26
to provide data communications over conventional
telephone lines 28, 28a, 28b with other elements of
-- 8 --
the system. Central also includes a telephone set
30 providing voice communications with other ele-
ments of the system over line 28.
The second subdivision oE the system is a
local panel 32 connected to central via telephone
line 28. Other local panels (not shown) can be
connected to central via telephone lines 28a, 28b
or additional telephone lines (not shown), as
needed. In general, local panel 32 includes a
telephone interface 33, a modulator 34, a demodu-
lator 35 and a microcomputer 36 connected to the
digital side of the modem. Connected to the micro-
computer are a number of local panel input and
output devices. Such devices include a keyboard
38, a test switch 39, light-emitting diode (LED)
displays 40, a reset button 41, security function
control switches 42, a siren 43, a prealarm speaker
44 and a fire detector 46. Also connected to
microcomputer 36 are an audio control means 45 and
; 20 a local-to-remote panel communications bus device
50 whose functions are described further herein-
after. The local panel also includes a power sup-
ply 48 operable from alternating current or direct
current, such as backup batteries, to produce vari-
ous voltage levels as described hereinafter.
The third subdivision oE the system
includes a remote panel 52, connected to the local
g
panel by four lines 54, 55, 56, 57. In one exam-
ple, there can be up to 256 remote panels, o~ which
remote panel A is shown in detail and similar
remote panels B, K and N are simply represented
symbolically.
Lines 54, 55, 56, 57 interconnect each of
the remote panels and the local panel. Data line
54 provides two-way data communications among the
panels. Power line 55 provides direct current
power to the remote panels. Line 56 provides a
common or floating ground to all panels. Voice
line 57 provides two-way voice communications from
the remote panels to the local panel and to central.
Each remote panel includes a remote-to-
local-communications bus device 58 connected via
data line 54 to communications bus 50 in the local
panel. Each remote panel also includes a remote
power supply 60 connected by po~er line 55 and
common line 56 to local power supply 48, and a
speaker-microphone intercom 6~ connected by voice
line 57 to audio control 45.
Connected to communications bus device 58
in each remote panel is a microcomputer 64 having a
number of input-output elements. Such elements
include a panic button 66, security monitors or
loop inputs 67, zone input switches 68, test and
display panel 69, a keyboard 70 r and a remote panel
-- 10 --
number or address switch 71. The microcomputer
also includes ports for other inputs and outputs 72
as may be selected by the user.
Bi-directional data communications on line
54 is controlled by a communication protocol and by
the handshake operation oE the local panel bus
device 50 with the remote panel bus devices 58.
Both the handshake operation and the communications
protocol are described in detail hereinafter. All
lQ remote panels "listen to" or receive all communica-
`~ tions on line 54, including communications from
other remote panels and communications from the
local panel. The local panel likewise listens to
all traffic on line 54. However, except as will be
described further in later sections, the remote
panels ignore transmissions from other remote pan-
els and only respond selectively to transmissions
from the local panel. Following is a discussion of
the message format employed in communications
between the local and remote panels.
Local-Remote Pan_l Message Format
Referring to Fi~. 2, data communications
between the local and remote panels employ
seven-byte ASCII basic messages or digital data
signals 74, 76 transmitted at 1200 band. Fig. 3
shows an example o~ a single local panel message 74
in time-expanded form.
- l:i --
~l~J6~
The first byte of each message is a com-
mand byte containing twelve bits, best seen in Fig.
3. The first three bits of the command byte are a
starting sequence. Bits 1 and 3 are zero-voltage
level start bits separated by bit 2 whose level is
+5 volts. Bit 1 has a duration of about 20 milli-
seconds if transmitted by the local panelO Other-
wise, its duration is 0.8 milliseconds. Bit 2 has
a duration of about 5 milliseconds. All of the
following bits in the message are 0.8 milliseconds
long. The following eight bits in the command
byte, that is, bits 4 through 11, form an ASCII
command word in which bit 4 is the least signifi-
` cant digit and bit 11 is the most significant
digit. Bit 12 is a stop bit which is always high~
that is, set to +5 volts.
The command word illustrated in Fig. 3 isa reset command. Many other command words are
used, including the following examples shown in
Fig. 2 A polling command 74a is used by the local
panel to selectively poll the remote panels. The
local panel enables the remote panels to transmit
data by issuing a grant command 74b. An answer
message 76 containing, for example, switch settings
or other requested data, is transmitted by a remote
panel in response to the polling signal or other
inquiry from the local panel. The local panel uses
- 12 -
an arm command to direct a remote panel to arm aspecified security loop. A repeat or ret~ansmit
command is used by the local panel to request the
remote panel to repeat its previous message. The
remote panel can also issue a repeat-request to the
local panel. Other commands can be added at the
user's choice.
Referring back to Fig. 3, the remaining
six bytes of ea~h message are, in form, identical
to one another. Each includes ten 0.8 microsecond
` duration bits commencing with a single zero-level
start bit and ending with a high (~5 volt) stop
bit. Bits 2 through 9 of each such byte form an
ASCII code word.
The second byte is a zone/dummy byte shown
in Fig. 3. The ASCII code word of bits 2 through 9
is used to identify a specific zone or condition to
be affected by the command word. If no zone or
condition is identified, a standard dummy se~uence
of bits is inserted in bits 2 through 9 of this
byte.
Following the zone/dummy byte are three
info/dummy bytes of ten bits each shown in Fig. 3.
The ASCII words of such bytes are used to transmit
general inormation, such as programming and status
information, between the remote and local panels.
If any such byte is unused to transmit information,
- 13 -
then the aforementioned dummy sequence is substi-
tuted.
A remote panel address byte follows the
three info/dummy bytes. In this sixth byte, the
ASCII word contains the address of the remote panel
to which the message is directed when transmitted
by the local panel. When a remote panel transmits
a message, it inserts its own address into bits 2
through 9 of the sixth byte.
The last byte in Fig. 3 is a cheGk-sum
byte, The ASCII word in this byte contains parity
and error correction information pertaining to the
previous six bytes of the message. If either the
local or remote panel detects and cannot correct an
error in transmission, it wil:l request retransmis-
sion of the message.
The local panel and all the remote panels
utilize the basic message format of Fig. 3, as
des~ribed above. However, the remote panels also
transmit a second kind of message, described in the
next subsection.
Remote/SRQ Signal
Since all remote panels communicate with
the local panel over line 54, it is necessary to
prevent multiple panels from attempting to transmit
simultaneously. To do so, the present invention
employs a data communications protocol, described
- 14 -
in a subsequent section. This protocol resemblesthe traditional classroom discipline which requires
students to raise their hands and be recogni~ed by
the teacher before speaking.
In the multiplex security system, the
remote panels must transmit a remote SRQ or request
signal 7~ (Figs~ 2, 3 and 5) before transmitting
- any message. The SRQ signal has a different ampli-
tude from the basic message amplitudes~ The SRQ
10 signal is preferably +8 to 20 volts, so as to be
readily distinguished from the zero and +5 volt
~ . .
levels of the basic messages 74, 76. ~owever, a
negative voltage could also be used for the SRQ
signal.
Referring to Fig. 2, the SRQ signal is
suppressed until an ongoing basic message, such as
message 74a, is completed. After a brief delay,
for example, 0.4 milliseconds, best seen in Fig. 3,
one or more remote panels can assert the SRQ sig-
;~ 20 nal. The duration of the SRQ signal, controlled by
the local panel, is typically 5 to 10 milliseconds.
The circuitry for generating the SRQ sig-
nal by the remote panel and interpretin~ it by the
local panel is described in the following section:
SRQ Generator-Detector_Circuit
As mentioned above, the local and remote
panels have complementary data communications bus
- 15 -
devices 50, 58~ These devices are representedgenerally in Fig. 1 and in greater detail in Fig. 4.
Referring to Fig. l, the local panel com-
munications bus 50 includes a bus driver 80, an SRQ
receiver 82 and a bus receiver 84. The remote
panel includes a bus driver 86, an SRQ driver 88
and a bus receiver 90. In the local panel, the bus
driver 80, the SRQ receiver 82 and the bus receiver
84 are all connected to line 54 at a common node
10 92. Similarly, in the remote panel, the bus driver
86 and SRQ driver 88 and the bus receiver 90 are
all connected to line 54 at a common node 94.
The bus drivers 80, 86 transmit the zero
to +5 volt basic messages under the control of the
microcomputers 36, 64 of their respective panels.
The bus receivers 84, 90 are comparators which
compare the data on line 54 with a +2.5 volt refer-
ence or threshold voltage to differentiate between
the zero and five volt levels of the basic mes-
20 sages. The SRQ receiver 82 is also a comparator.
It compares the data on line 54 with a +7.5 volt
reference voltage to differentiate between the
basic messages 74, 76 and the SRQ signal 78.
Referring to Fig. 4, the local panel bus
driver 80 includes an open collector buffer ampli-
fier 96 and a resistor 98 connected in series
between node 92 and microcomputer 36, and a pull-up
- 16 -
2~i;
resistor 100 and diode 102 connected in seriesbetween node 92 and the +5 volt output of power
supply 48.
The SRQ receiver 82 is a volta~e com-
parator having its negative side connected to node
92 and its positive side connected through resistor
104 to the ~10 volt output of voltage supply 48 and
through resistor 106 to the common ground. Resis
tors 104 and 106 are proportioned to provide the
aforementioned +7.5 volt reference voltage to the
positive side of the comparator.
The bus receiver 84 is also a voltage
comparator having its negative side connected
through resistor 108 to node 92. Its positive side
is connected through resistors 110, 112 to the +5
volt and common ground connections, respectively,
of supply 48. Resistors 110 and 112 are propor-
tioned to provide the aforementioned +2.5 volt
reference voltage~ The output of comparator 84 is
connected to microcomputer 36 through an inverter
amplifier 114. A feedback resistor 116 is con-
nected between the positive input and the output of
comparator 84. Two equal size resistors 118 con-
nect the outputs of comparators 82, 84 to the +5
volt source. A diode 119 connects the negative
input of bus receiver 84 to the +10 volt output of
the power supply to prevent the voltage on such
input from exceeding ~10 volts.
- 17 -
?26
The remote panel bus driver 86 includes an
inverter 120 and an output resistor 122 connected
in series between the microcomputer 64 and node
94~ The SRQ driver 88 includes an inverter 124 and
a diode 126 connected in series between the micro-
computer and node 94. A resistor 128 is connected
between the output of inverter 124 and the +Vcc
voltage output of power supply 50. Bus receiver 90
is a voltage comparator having its negative lead
10 connected through resistor 130 to node ~4 and its
positive side connected to a +2.5 volt reference
voltage~ The output of comparator 90 is connected
to mîcrocomputer 64 through an inverter 132. A
feedback resistor 134 is connect'ed between the
output and the positive input of the comparator.
The input and output of the inverter are connected
through different value resistors 136, 138 to the
~5 volt output of power supply 60.
In a specific example, the local panel
microcomputer 36 is an Intel 8748-8, bus driver 80
is a Texas Instxuments 7417 buffer and receivers
82, 84 are National Semiconductor LM 339 com-
parators. Continuing the example, the remote panel
microcomputer 64 is an Intel 8048-8. Inverters
120, 124 are Texas Instruments 7416 inverters.
Comparator 90 is an LM 339 comparator. The values
of resistors 98 and 128 are 180 ohms and 24
- 18 -
kilohms, respective1y. The reasons for these pro-
portionate values are discussed hereinafter.
Resistance values for the rest of buss devices 5
and 58 are as follows: resistor 108 -- 20 kilohms,
resistor 122 -- 180 ohms, and resistor 130 -- 24
kilohms.
During normal transmission of the basic
messages or data signals 74, 76, only bus drivers
80, 86 and bus receivers 84, 90 are used. For
lO example, when the local bus driver is transmitting
a message from the local panel, the voltage levels
on line 54 switch between zero and +5 volts. These
voltage levels are compared by remote panel bus
receiver 90 with the a~orementioned ~2.5 volt
reference level. Conversely, when the remote panel
bus driver 86 transmits, local panel bus receiver
84 compares the zero to +5 volt levels of the basic
messages with its +2.5 volt reference input and
switches to transmit an output si~nal to microcom-
20 puter 36. ~he SRQ receiver 82 also receives thezero to +5 volt messages transmitted by both bus
drivers 80, 86 but, comparing such signals with its
+7.5 volt reference level, it does not switch and
produces a steady-state zero output signal to
microcomputer 36.
To assert the SRQ signal, the remote panel
microcomputer 64 generates an SRQ input signal to
-- 19 --
3t~i
the SRQ driver 88. Inverter 124 normally holds
diode 126 in a reverse biased, nonconducting condi-
tion so that voltage ~Vcc through resistor 12~ is
blocked and thus does not appear at node 94. The
SRQ input signal is inverted by inverter 124, for-
wardly biasing diode 126 and enabling voltage
~Vcc to pass through such diode and node 94 onto
line 54 as SRQ signal 78. Voltage +Vcc thus
appears at the negative input to the SRQ receiver
10 comparator 82 in the local panel. This voltage is
compared with +7~5 volts on the positive input of
such comparator to produce an SRQ output signal to
microcomputer 36. The SRQ signal (clipped to +10
volts by diode 119) is also compared in the local
panel bus receiver 84 with its +2.5 volt reference
level to produce a second SRQ output signal as a
data signal to microcomputer 36. However, suitable
programming enables the latter signal to be ignored
by microcomputer 36, as described hereinafter,
Upon receiving the SRQ input signal,
microcomputer 36 generates an acknowledgment or
grant command message in accordance with the basic
message format of Fig. 3. As described above, the
first bit of such message is a zero. For the dura-
tion of such bit, approximately 20 milliseconds,
buffer 96 essentially grounds line 54, causing a
current flow from voltage input +Vcc through
- 20 -
resistors 128 and 98. Because of the great dispar-
` ity in value between these two resistors, substan-
tially all of the voltage drop appears across
resistor 128, thereby reducing the voltage appear-
ing on line 54 essentially to zero within 5 to 10
ms of the commencement of the SRQ signal.
Remote panel bus receiver 90 receives the
SRQ signal and, comparing such signal with ~2.5
volts, presents a continuous high logic level to
10 microcomputer 64 for the duration of the SRQ sig-
nal. When the local panel transmits bit 1 of the
grant command, causing the voltage on line 54 to
drop below +2.5 volts as a result of operation of
bus driver 80, bus receiver 90 senses the voltage
drop and begins to transmit a continuous low logic
level signal to microcomputer 64 for the remaining
duration of bit l--about 10 to 15 ms. Internal
programming responsive to this signal change causes
microcomputer 6~ to turn off the SRQ input signal
to the SRQ driver and prevents its being turned on
again until after transmission is completed o both
the local panel acknowledgement message and the
nex~ message transmitted by an~ remote panel.
The use of the foregoing message format
and signals to discipline data communiGations
between the local panel and the remote panels,
along with the internal programming of the micro-
- 21 -
2~i
computers, is described in the following section,with reference to Figs. 2, 5, and 6.
Local-Remote Panel Communications Protocol
Referring to Fig. 2, the data transmitted
on line 59 includes local panel messages 74, remote
panel messages 76 and remote SRQ signals 78. As
mentioned above, the local and remote messages 74,
76 employ essentially the same format. EIowever, in
the remote panel messages 76, bit 1 of the command
10 byte is of the same duration as all of the remain-
ing bits.
When the multiplex security system is
first turned on, and from time to time during its
operation, the local panel transmits the status
command 74. This command causes the remote panels
to reset to certain functions including displays,
loop and zone inputs and the like. This step is
indiGated by blocks 149, 151, 152 at the beginning
of the flow chart of Fig. 6.
Following reset, the local panel will
ordinarily issue a series of commands, indicated in
block 153, arming or setting specific security
functions in the remote panels. These commands can
be initiated manually from the keyboard 38 in the
local panel, generated indirectly from the remote
panel by stored programs in the local panel, or
initiated by the central computer, as indicated by
- 22 -
~63~2~
blocks 155a, b and c in Fig. 6. These commands can
be directed to all remote panels or can be
addressed to a specifiG remote panel. Referring to
blocks 157, 159, the remote panels await these
further command messages and upon receiving them,
decode and impLement the commands.
After the programming of the remotes is
complete, the local panel microcomputer begins
processing a main monitor program as indicated by
block 161. This program generates additional com-
mand messages to the remote panels such as a
polling command message 74a in Fig. 2. Referring
to the flow chart, the remote panels decode and
implement such commands in the same manner as dur-
ing the programming step.
In response to a polling command received
by block 163, the remote panel microcomputers com-
pare the address contained in byte 6 of the polling
command message with their respective assigned
remote panel switch numbers as indicated by block
167. In one of the remote panels, such as panel A,
the address compares with its switch number as
indicated by the yes output (y) of block 167, caus-
ing such panel to enable its SRQ driver (block
171). The remaining panels return to internally
programmed tasks, such as monitoring their respec-
tive re~ote inputs for alarm conditions (blocks
- 23 -
z~
170, 172). Detection of an alarm condition such assetting of panic switch 66 or a break ln a loop
input 67 in Fig. 4 will also cause the remote panel
to enable SRQ. Likewise, detection of a data
transmission error (block 173) from the local panel
will cause enabling of SRQ so that the remote panel
can request retransmission. If no such error is
detected, the message is processed per block 175.
All local panel messages are initially processed
through block 173.
Remote panel A, whose SRQ driver was
enabled, transmits an SRQ signal on line 54 (Figs.
1 and 4). This signal is received by the local
panel SRQ receiver 82 and provided to microcomputer
36. Receiving the SRQ signal (block 174), the
local panel microcomputer responds by transmitting
(block 176) a grant command message 74b, as shown
in Figs. 2 and 5.
~Referring to blocks 178, 180, 182 in Fig.
-~20 6, remote panel A receives the grant command, dis-
ables the SRQ driver and reads its remote panel
switch numbers, which can range from zero to 255.
If the remote panel switch number equals zero
(block 184), the remote panel immediately causes
the bus driver 86 to commence transmitting the data
requested to the local panel (block 194) during the
zero time interval 77 (Fig. 5).
- 24 -
If the remote panel switch nurnber does not
equal æero, the remote panel counts time intervals
(blocks 186, 188). The number of time intervals
equals the maximum number of remote panel switch
numbers. The duration of these time intervals is
200 microseconds. When the number of time inter-
vals equals the address in the polling message,
indicated by a yes output (Y) of block 188, micro-
computer 64 checks the input of its bus receiver to
10 see if another panel is already transmitting ~block
190). If another panel is transmitting, remote
panel A waits until such transmission is complete
(block 192). At that point, it returns to block
171 and again enables its SRQ driver. If no other
panel is transmitting, panel A causes its bus
driver to commence transmitting the requested data
signal 76 to the local pane:L (block 194) during
timing interval 77a, as shown in Fig. 5.
Referring to blocks 196, 198, the local
20 panel receives this data from the remote panel and
checks it for errors. If any uncorrected errors
remain, the local panel sends a retransmit command
to the remote panels (block 199), causing remote
panel ~ to repeat the above-described counting and
transmitting steps. Each of the remote panels
treats the retransmit command as a grant command,
again disabling their SRQ drivers until retransmis-
sion is complete.
- 25 -
~ii3~
Once the local panel has received correct
data from the remote panel in response to a polling
command, as indicated by the no output (N) of block
198, the data decoded in block 197 is provided to
the main monitor program (block 162) Eor process-
ing. Then the local panel checks to see if an SRQ
siynal has again been asserted (block 174). If no
such signal has been asserted, the main monitoring
program continues polling.
Referring to Figs. 2 and 5, the next
polling signal is message 74c addressed to remote
panel M. Remote panel M responds by transmitting
SRQ signal 78a, as shown in Figs. 2b and 5b. The
local panel replies with grant command message 74d
causing all of the remote panels to disable their
SRQ drivers and to proceed to count up to their
respective remote panel switch numbers, as previ-
ously described. In this particular example,
remote panel B has an alarm indicator which has
been set, for example, in response to an alarm
condition detected on one oE the loop inputs to
such panel. Panel B has a lower remote panel
switch number than panel M on a correspondingly
earlier time slot 77b. Accordingly, panel B com-
mences transmitting message 76a before panel M can
respond~
- 26 -
As soon as the transmission of message 76a
is complete, remote panel M again enables its SRQ
driver, causing SRQ signal '78b to be transmitted.
In response, command grant message 74e is trans-
mitted and the SRQ driver of remote panel M is
turned off. If, for example, remote panel K now
has an alarm condition to report, and its remote
panel switch number is of higher priority than that
of panel M, panel K will begin transmitting message
76b during its assigned time interval 77d ahead of
panel M.
Referring to Fig. 2, panel M will again
; assert its SRQ signal 78c upon the completion of
the transmission of message 76b. Following grant
command 74f and counting of the number of time
intervals corresponding to its switch number,
finally is given the opportunity to respond and,
thus, transmits message 76c. Then, the polling
process resumes. The local panel polls remote
panel N by transmitting message 74g and panel N
responds by asserting SRQ signal 78d. And then the
above-described process is repeated.
Thus, the local-remote panel communica-
tions protocol permits the local panel to routinely
poll the remote panels while allowing remote panels
having urgent messages to interrupt the normal
polling process and transmit their more urgent
- 27 -
message. The counting of time intervals duringwhich remote panel transmissions can be commenced
and comparison of the count with remote panel
switch numbers provides both a prioritization means
and a means for time-multiplexing messages from the
remote panels. In this connection, it should be
remembered that~ before a remote panel can transmit
a message, it must transmit an SRQ signal and the
local panel must acknowledge such signal with a
10 grant command. Only then can that or another
remote panel transmit a message to the local panel.
The remote panel switch numbers can be set
manually at the remote panel, or can be programmed
by the local panel or central computer via the
local panel. In this example, it i5 assumed that
each remote panel has 8 remoke panel switch numbers
; which can be set, and that there are up to 256
remote panels. However, both can be changed to
accommodate larger numbers of both remote panels
20 and securit~ functions per remote panel.
Voice-Data Switching
This section describes the interaction of
the data communications between the local and
remote panels with the voice communications between
such panels and with the central. As mentioned
above, each remote panel has associated with it a
speaker/microphone. The microphones are of the
- 2~ -
highly sensitive type used for detecting intrud-
ers. The local panel has a prealarm speaker 44 for
providing prealarm sound in a burglar entry sensing
mode. The local panel also has a siren 43. Audio
control 45 controls the operation of the sirens and
the prealarm speaker, and enables the telephone
interface between the local panel and central to be
used to alternately transmit voice and data com-
munications.
Referring to Fig. 4, the audio control
includes a pair of siren drivers 43 connected to
microcomputer 36. The siren drivers are connected
to sirens 43 and are also connected in series with
a resistor 150, a capacitor 152, and a field effect
transistor 154. An inverter 1S6 provides a pre-
alarm enable/disable signal from microcomputer 36
to the node between resistot 150 and capacitor
152. Connected to a node 158 between capacitor .L52
and field effect transistor (FET) 154 are the end
20 Of voice line 57, a resistor 160 connected at its
opposite end to the common floating ground and the
prealarm speaker 44. The gate of transistor 154 is
conne~ted through an expander chip 36b to microcom-
puter 36~ Also connected to the FET gate is an
inverter 160 whose output is connected to the gate
of a second field effect transistor 162. This
latter transistor is connected between the output
- 29 -
of modulator 34 and the output of transistor 15~ atnode 164. This node is connected to one side of an
isolation transformer 166, which is part of -the
telephone interface 33, and to the input of the
demodulator 35. I'he telephone interface is also
connected to the microcomputer 36 by two lines, a
ring line 168 and a dial and connect line 169, as
further described hereinafter.
During transmission of the data through
10 the modulator/demodulator, that is, between the
local panel and central, gate 154 is turned off and
gate 162 i5 turned on. To transmit voice informa-
tion, microcomputer 36, responding to either a
telephone input (not shown~ at the local panel or
to a voice input at speaker/microphone 62, causes
gate 154 to switch on and gate 162 to switch off,
blocking further transmission of data and enabling
transmission of voice information through the tele-
phone interface.
To actuate the prealarm speaker, microcom-
puter 36 transmits a si~nal through gate 156 to
turn on the speaker.
To actuate the sirens, for example, in
response to an alarm from fire detector 46, the
microcomputer generates signals to the siren
drivers 43a which drive sirens ~3. This signal is
also transmitted through resistors 150 and capaci-
- 30 -
3~
tor 152 to line 57 so that the siren driver signal
is applied to speaker 62. By operation of gates
154, 162, the siren driver signal can also be
transmitted throuyh the telephone interface to
central. Alternatively, and simultaneously with
actuation of the siren drivers, microcomputer 36
can dial and ring through the telephone interface
to central.
Central-~ocal Communications
As mentioned above, data can be trans-
mitted in both directions between central and the
local panels via telephone line 28. Such trans-
missions can be initiated from either end. Nor-
mally, the telephone line is idle.
The central computer initiates communica-
tions with a local panel ~y transmitting a ringing
signal from modem 24. This signal is received by
telephone interface 33 and transmitted across an
optical coupler (not shown) to ring line 16~. This
ZO signal is input to microcomputer 36 which responds
by causing modulator 34 to transmit a tone, for
example, at 1000 Hz. Simultaneously, the microcom-
puter disables the gate of FET 154 and enables the
gate of FET 162 to place the tone on the telephone
line. This tone continues for about 5 seconds.
The central modem 24 receives the tone and so sig-
nals the digital computer 22. The computer then
,
commences transmitting 4 to 15 byte messages in
ASCII code to local.
In this way, central can initiate a varie-
ty of actions which affect the local panels or
cause one or more of the local panels to take some
action affecting their respective remote panels.
Central can intermittently poll the local panels to
determine their status and the condition of their
telephone lines. Similarly, central can read any
10 switch settings at a remote panel. Central can
also transmit or download security programming,
such as loop number, type of loop and arm codes to
any remote panel via its local panel. Central can
likewise troubleshoot hardware failures at the
remote panels.
Once central has initiated communications
of the telephone line, the local panel can transmit
message to central spontaneously as well as in
response to requests from central. However, a
20 local panel can also open the telephone line to
initiate communications with central. To do so~
microcomputer 36 sends a connect and dial signal
via line 169 to the telephone interface~ This
signal is transmitted to relay circuitry in the
telephone interface which dials through to cen-
tral. Central answers the call by transmitting a
5-second tone from modem 24 to the local panel.
- 32 -
This tone is received by demodulator 35 which sig-
nals the microcomputer 36. The microcomputer then
disables FET 15~, enables FET 162 and begins trans-
mitting 4 to 15 byte ASCII messages to central.
These messages are demodulated by modem 24
and stored in a buffer memory (not shown) until the
digital computer is ready to process the informa-
tion. The computer then services the information
in order of its priority. A burglar alarm or other
mergency message is serviced before a nonemergency
message, such as a test report.
The interaction of voice and data trans-
missions between a remote panel and central is more
readily apparent from the following example.
Assume someone activates panic switch 66 or an
intruder trips a loop input 67. The remote panel
microcomputer immediately recogni~es these inputs
as an alarm condition (Block 172 in Fig. 6). It
then enables transmission of an SRQ signal such as
20 signal 78 in Fig. 2. This signal is acknowledged
by a grant command ~rom local. Since remote pan-
els with a panic switch or intruder entry alarm are
assigned remote panel switch numbers of relatively
high priority, such remote panel is ordinarily able
to transmit its alarm message quite quickly.
; Referring to Fig. 2, this message can be trans-
mitted in as little as 160 milliseconds. Even if
- 33 -
3~
the particular remote panel were assigned a panel
switch number of 250, the alarm message would be
transmitted within 2/3 secondO
Upon receipt of the alarm message, the
- local panel initiates communications with central
as desGribed above. If the alarm condition is a
loop input ~hat has been tripped, the local panel
microcomputer 36 transmits pertinent data to cen-
tral in ASCII code, leaving FET 162 enabled for
10 continuing data communications.
If the alarm condition is the panic
switch, the local panel enables voice communica-
tions from the remote panel to central via the
speaker/microphones. Upon receipt of the panic
switch message, the local panel initiates communi-
cations with central as described above. ~owever,
as soon as central responds with a tone, the loGal
panel microcomputer disables FET 162, blocking
further transmissions from modulator 34. FET 154
20 is simultaneously enabled so that the person who
activated the panic switch can talk to someone at
central via speaker/microphone 62, voice line 57,
telephone line 28 and telephone set 30.
Voltage Regulated Power Supplies
Referring to Fig. 1, the multiplex securi-
ty control system is designed to be run from AC
power with backup DC batteries~ An AC/DC loss
- 34 -
~63~2~
detector 200 signals microcomputer of loss of ACpower. The microcomputer in turn signals central
and switches to the batteries. When fully charged,
these batteries provide 13.6 volts of power.
The power supply 48 has two parts, best
seen in Fig. 4. One part is a conventional AC/DC
power supply 48a whose outputs are +Vc~, which is
an unregulated direct current voltage level which
typically ranges from 8 to 20 volts, a regulated +5
10 volt level and a floating ground or common.
The second part of the power supply is a
regulated 10 volt supply 48b. This portion of the
power supply is designed to provide a regulated 10
volts direct current even when the power supply is
; being powered by batteries which have run down to
less than 10 volts. Power supply 48b includes a
circuit portion 170, including, for example, a 555
pulse generator, which chops the DC voltage level
+Vcc into a periodic signal, such as a square
20 wave with a peak-to-peak voltage amplitude of as
; close as possible to ~Vcc. This signal is
applied to one side of a large value capacitor
172. Voltaye Vcc is connected through a recti-
fier 174 to the opposite side of capacitor 172.
This junction is connected through a second diode
176 to a 5 volt regulator 178. Between diode 176
and the 5 volt regulator is a second large value
- 35 -
~L63~
capacitor 180 connected to the Eloating ground.
The 5 volt regulator is connected to the -~5 volt
lead of supply portion 48a. ~he output of the
voltage regulator is connected to a third capacitor
182, which is in turn connected to ground. This
last capacitor provides a regulated 10 volts level
which is used by the modulator and demodulator and
by comparator 82.
: Having illustrated and described a pre-
10 ferred embodiment of my .invention, it should be
apparent to those skilled in the art that the
invention can be modified in arrangement and
detail. Accordingly, I claim as my invention all
apparatus falling within the spirit and scope of
the following claims.
- 36 -
