Note: Descriptions are shown in the official language in which they were submitted.
2 1 86 794
Automatic Dialin~ Mode Scl~lior
kg~Qund Of tl~e Invention
The invention relates generally to telephony, and more particularly to techniques
for selecting an approp~iate dialing mode for telephonic devices.
5 2. nes~ lionofPriorArt
The dialing mode of telephonic devices must be set to specify the a~propliate
dialing mode, such as pulsed dialing or touch-tone dialing. State-of-the-art telephonic
devices do not include any means by which the capabilities of a given tip-ring connection
may be automatically checked to determine the a~pi~liate dialing mode. Although
10 many tip-ring lines connected to the Public Switched Telephone Network are equipped to
accept touch-tone dialing signals, other tip-ring lines will only accept pulsed dialing
signals. The device user must m~ml~lly select an app,~liate dialing mode by setting a
slide switch to a first position corresponding to touch-tone ~ lin~, or to a second position
corresponding to pulsed ~ ling
Telephonic device users are required to know the dial sign~lin~ capabilities of a
given tip-ring line in order to select the proper dialing mode. Of~elltimes~ the dialing
mode is not known, and, as a result, the slide switch is not set to the proper position. If
the switch is set to pulsed dialing when the tip-ring line is equipped to implement touch-
tone sign~ling, the device user will not benefit from the ~ltili7~tion of touch-tone
20 si~n~lin~- The telephonic device will take a long time to place an outgoing call relative
to other telephonic equipment that the user may have employed in the past. If the user
~llelll~ to access services that utilize end-to-end touch tone sign~ling, such services will
be rendered inoperative. On the other hand, if the switch is set to touch-tone dialing when
the tip-ring line is only equipped to implement pulsed di~ling, the device user will not be
25 able to originate any outgoing telephone calls. When the dialing mode slide switch is not
set to the proper position, the user may return the device to the seller because the device is
perceived as having relatively poor p~_lrol.llance.
2 21 867~4
What is needed is a technique for automatically detc~ the dialing mode
capabilities of a tip-ring line, and for automatically setting the dialing mode of a
telephonic device to specify the appr~1iate dialing mode. Such mode setting should take
place when the telephonic device is first connected to the tip-ring line, and the mode
setting should remain in force until the telephonic device is removed from that tip-ring
line. However, an option may be provided for the user to specify mode setting for the
duration of a telephone call after the call has been established by the PSTN (public
switched telephone network), thereby permitting the user to access interactive touch-tone
services from a tip/ring line equipped to implement only pulsed dial si~n~lin~ for
o purposes of call establishment.
y of ~he ~r vention
Automatic dialing mode selection techniques are ut~ e~l in the operational
environment of a telephonic device connected to a tip-ring line. The telephonic device
includes dialing mode assessment ch~ y and dialing mode setting cil'cuilly. The
dialing mode ~sessment circuitry automatically determines the dialing mode supported
by the tip-ring line. The dialing mode setting circuill ~ is responsive to the dialing mode
assessment circuilly for automatically setting the dialing mode of the telephonic device to
specify the dialing mode supported by the tip-ring line, such as pulsed dialing or touch-
tone lli?ling. The dialing mode is automatically set at the time that the telephonic device
is first connected to the tip-ring line, and the telephonic device retains that mode setting
until the device is removed from the tip-ring line.
Brief l)escriptior of the l)rawin~
FIG. 1 is a har.lw~e block diagram setting forth an illustrative embodiment of the
automatic dialing mode selection system disclosed herein;
FIG. 2 is a flowchart describing a first sequence of operations implemented by the
system of FIG. l; and
3 2186794
FIG. 3 is a flowchart describing a second sequence of operations implemented by
the system of FIG. 1.
l)etailed ~escription of the Preferred Embodiments
FIG. 1 is a hardw~e block diagram setting forth an illustrative embodiment of the
automatic dialing mode selection system 100 disclosed herein. Automatic dialing mode
selection system 100 may be used in conjunction with, and/or incorporated into, virtually
any telephonic device that is equipped to interface with a tip/ring line 121. A polarity
guard 101 circuit is connected across tip/ring line 121. Polarity guard circuit 101 includes
four semiconductor diodes in a bridge rectifier arrangement, and enables the automatic
dialing mode selection system 100 to function properly, independent of the actual polarity
of the DC voltages on tip/ring line 121. Polarity guard circuit 101 is coupled to a line
switch 105, which may be an electronic, electromechanical, or mechanical line switch of
conventional design. An optional mechanical hook switch 103 is present if, for example,
the telephonic device consists of a POTS telephone (plain old telephone set). This
mechanical hook switch 103 is coupled to line switch 105.
A first energy storage device is employed to store electrical power while the
automatic dialing mode selection system 100 is in an on-hook state with respect to
tip/ring line 121. In the present example, this energy storage device consists of an
electrolytic capacitor 104 which is charged through an isolation resistor 102. Electrolytic
capacitor 104 is selected to have a relatively high capacitance value of, for example, 1000
microfarads or greater, and as low a value of leakage current as is practicable. The DC
potential across capacitor 104 is coupled to a first input tçrmin~l 151 of a power supply
control circuit 126. The DC potential across capacitor 104 is also coupled to a first input
tçrmin~l of a second voltage sense circuit 135.
A second energy storage device is employed to store electrical power while the
automatic dialing mode selection system 100 is in an off-hook state with respect to
tip/ring line 121. In the example of FIG. 1, this second energy storage device consists of
~ ~ 21 ~6794
an electrolytic capacitor 108 which is charged through an isolation resistor 106. An
ind~lctor having a relatively high impedance at audio frequencies may optionally be
placed in series with isolation resistor 106 (or, alternatively, used in place of isolation
resistor 106) to minimi7e the extent to which the combination of eleçtrolytic capacitor
108 and isolation resistor 106 ~ttenl-~te the audio frequency range. Electrolytic capacitor
108 is selected to have a relatively high capacitance value of, for example, 1000
microfarads or greater, and as low a value of leakage current as is practicable. A
rechargeable battery could be used in place of electrolytic capacitor 108 if desired. The
DC potential across capacitor 108 is coupled to a second input tPrmin~l 153 of power
o supply control circuit 126.
An optional power source 113 is coupled to a third input termin~l 155 of power
supply control circuit 126. This power source 113 may comprise, for example, an AC
adapter that converts conventional residential AC current into a low-voltage DC current.
Such AC adapters typically include a power transformer that steps down this AC voltage
(nominally 117 volts AC or 220 volts AC, depending on location) to a lower voltage level
(e.g., 6.3 or 12.6 volts AC). The stepped-down AC voltage is applied to a diode bridge
rectifier and the rectified DC voltage is filtered by means of an electrolytic capacitor.
Alternatively, power source 113 may comprise a rechargeable battery, a non-rechargeable
battery, and/or a rechargeable battery combined with an AC adapter and battery-charging
Cil~;uill~.
Power supply control circuit 126 selectively applies DC power to a main power
128 output t~rmin~l and/or a backup power terminal 130 based upon the presence or
absence of DC power at each of the input termin~l~ 151, 153, 155 of the power supply
control circuit. For example, if power is present at all ofthe input termin~l~ 151, 153, and
155, then power supply control circuit 126 applies DC power to both the main power 128
output and the backup power 130 output. However, if power is present at first input
terminal 151, but no power is present at second and third input termin~l~ 153, 155,
5 2186794
respectively, then power supply control circuit 126 only applies powér to the backup
power 130 output and not to the main power 128 output. The backup power output 130
of the power supply control circuit 126 is coupled to a second input of the second voltage
sense circuit 135. In practice, various combinations of transistors, diodes, other
semiconductor devices, and/or logic gates may be employed to implement power supply
control circuit 126. The construction of a suitable circuit for power supply control circuit
126 is a matter within the knowledge of those skilled in the art.
An electronic line switch may be employed for line switch 105 or, ~Itern~tively,line switch 105 may be a mechanical line switch. In the example of FIG. 1, line switch
o 105 is coupled to an optional mechanical hook switch 103. Conventional components
may be used to fabricate line switch 105 and mechanical hook switch 103. Line switch
105 is provided with a first port, a second port, and a control port for selectively enabling
and disabling a commlmications pathway between the first and second ports. Polarity
guard circuit 101 is coupled to the first port of line switch 105, and the control port of line
switch 105 is coupled to microcontroller 115. The second port of line switch 105 is
coupled to a voice hybrid network 111, and this second port is also coupled to a dial tone
detector 107. The output from a DTMF tone generator 109 is coupled to voice hybrid
network 111. The operation of DTMF tone generator 109 is controlled by
microcontroller 115.
Voice hybrid network 111, DTMF tone generator 109, and dial tone detector 107
are components of conventional design, the details of which are generally known to those
skilled in the art. For example, dial tone detector 107 may include an energy detector for
detecting the presence of dial tone on tip/ring line 121. Dial tone detector 107 is coupled
to microcontroller 115, and sends microcontroller 115 a signal indicative of whether or
not dial tone exists.
A first voltage sense circuit 125 senses voltage on main power terminal 128, andthe second voltage sense circuit 135 senses voltage on voltage storage device 104. The
6 21 ~6794
first voltage sense circuit 125 is coupled to a first pulse generator 132. Upon sensing a
voltage level above a predetçrrnined threshold, the first voltage sense circuit 125 activates
the first pulse generator 132 to apply a pulse to the RESET termin~l of microcontroller
115. The first pulse generator 132 is powered from main power tetrnin~l 128. In this
s manner, the combination of first voltage sense circuit 125 and first pulse generator 132
function as a power-on-reset circuit element that is responsive to voltage on main power
termin~l 128 to reset microcontroller 115.
Microcontroller 115 may be implemented by a conventional microprocessor of a
type well-known to those skilled in the art, and is coupled to an associated random-access
o memory (RAM) circuit 122. Microcontroller 115 uses RAM 122 to store a mode control
bit that indicates whether tone or dial pulse sign~lin~ is to be used. RAM 122 is coupled
to main power 128 as well as backup power 130.
The operation of line switch 105 is controlled and monitored by a microcontroller
115. As previously stated, microcontroller 115 also controls the operation of DTMF tone
generator 109. DTMF tone generator 109 is employed for the purpose of dete- .. i~ the
dial sign~ling capabilities of tip/ring line 121, as will be described in greater detail
hereinafter. The DTMF tone generator 109 is also used to place outgoing telephone calls
and to access on-line interactive services that use DTMF si~lin~;.
The output of second voltage sense circuit 135 is coupled to a second pulse
generator 143. When activated by the voltage sense circuit 135, which occurs when
voltage sense circuit 135 senses a voltage above or below a predeterrnined threshold, the
second pulse generator 143 applies a pulse to a reset input of latch 148. Latch 148 may
be implemented using a conventional latch device. A set input of latch 148 is coupled to
microcontroller 115. The output of latch 148 is concept~l~li7çd as l~resentin~ an "ID
bit". The value of this ID bit is forwarded to microcontroller 115 to indicate the time at
which the sequence to set the dialing mode must be pe.ro~ ed.
7 21867~4
Microcontroller 115 may be coupled to an optional display device for providing an
indication as to the dialing mode capabilities of tip/ring line 121, an indication as to the
operations presently being pc.rolllled by automatic dialing mode selection system 100,
and/or user plo.ll~ so as to enable a proper determin~tion of dialing mode at the proper
s time, as when the telephonic device is connected to a new tip/ring line.
The embodiment of FIG. 1 is used in conjunction with telephonic devices that arebattery-powered, and/or powered from a conventional AC (~Itern~ting current) wall
outlet. Such telephonic devices include telephone answering m~cllines, cordless
telephones, fax machines, many present-day electronic telephones with enhanced fealules
that require a steady source of power, as well as other types of equipment that may be
connected to a tip/ring line. The embodiment of FIG. 1 also operates in conjunction with
plain, old telephone devices, also known as "POTS" telephones, which do not generally
include power source 113. If it is desired to equip a POTS telephone with enhanced
features requiring the use of active semiconductor devices, these devices must thc.cfolc
be powered up using energy extracted from tip/ring line 121.
In the case where automatic dialing mode selection system 100 is employed in theoperational environment of a POTS telephone that does not include a power supply, the
system opc.ates as follows. Tip/ring line 121 is connected to a polarity guard circuit 101
which, in the present example, includes four diodes arranged in a conventional bridge
rectifier configuration. While a POTS telephone is on-hook, in most cases, insufficient
power exists to operate microcontroller 115. However, the bridge rectifier of polarity
guard circuit 101 delivers a DC voltage of a given polarity to capacitor 104, independent
of the actual polarity of the DC voltages on tip/ring line 121. These DC voltages may be
used to trickle-charge an energy storage device, which, in the present example, consists of
electrolytic capacitor 104 which is charged through isolation resistor 102. Electrolytic
capacitor 104 is selected to have a relatively high capacitance value of, for example,
1,000 microfarads or greater, and as low a value of leakage current as is practicable.
8 2 1 86794
An inductQr having a relatively high impedance at audio frequencies may
optionally be placed in series with isolation resistor 102 to minimi~e the extent to which
the combination of capacitor 104 and resistor 102 attenuate the audio frequency range.
The DC potential across capacitor 104 is used to power DC power supply control circuit
126 and latch circuit 148. The DC potential across capacitor 104 may also be used to
power RAM 122 when RAM 122 is in a standby mode. In standby mode, RAM 122
retains the contents of its memory, but devices external to RAM 122 are not able to read
the contents of RAM 122, nor are such external devices able to write to RAM 122.First voltage sense circuit 125 detects the presence of tip/ring voltage at the output
of polarity guard 101. This voltage sensing circuit may include, for example, a Zener
diode and/or a comparator device.
When the POTS telephone is off-hook, sufficient power exists on tip/ring line 121
to power microcontroller 115 and RAM circuit 122 using a power supply circuit
con~i~ting of an isolation resistor 106 and a capacitor 108. An induGtor having relatively
high impedance at audio frequencies may optionally be placed in series with isolation
resistor 106 to minimi7e the extent to which the combination of resistor 106 and capacitor
108 attenuate the audio frequency range. Microcontroller 115 includes a DC powersupply input which is connected to main power 128. Upon the occurrence of an off-hook
condition, power supply control circuit 126 couples this DC power supply input to
capacitor 108 through a current limiting resistor 106. In the case of a POTS telephone,
line switch 105 may, in fact, represent a mechanical switch hook. Altern~tively, the
mechanical switch hook 103 of a conventional POTS telephone may be coupled to line
switch 105, as shown in FIG. 1. The POTS telephone is placed in the off-hook condition
by operation of mechanical switch hook 103 andtor line switch 105. In the off-hook
condition, the output of polarity guard 101 is connected to voice hybrid network 111, dial
tone detector 107, and power supply isolation resistor 106. When off-hook, DC power
for RAM circuit 122 is supplied by capacitor 108 and resistor 106 via power supply
2 1 86794
.
control circuit 126 and main power 128. When on-hook, DC power for RAM circuit 122
is supplied by capacitor 104 and resistor 102 via power supply control circuit 126 and
backup power 130.
Microcontroller 115 may be implemented using a generally available
microprocessor of conventional design. A microprocessor should be selected that has a
relatively low current drain, due to the fact that the microprocessor is to be powered from
the tip/ring line 121, and not from a continuous power supply. The microcontroller 115 is
coupled to RAM circuit 122. Although RAM circuit 122 and microcontroller 115 areshown as separate elements in the configuration of FIG. 1, RAM circuit 122 could be
o combined with microcontroller 115 in the same integrated circuit package.
As previously stated, microcontroller 115 controls the operation of a DTMF tone
generator 109. In response to microcontroller 115 comm~n~ signals, DTMF tone
generator 109 produces DTMF tones which are coupled through voice hybrid network111 and polarity guard 101 to tip/ring line 121. Dial tone detector 107 detects the
presence of dial tone on tip/ring line 121, and signals the microcontroller 115 as to the
presence or absence of dial tone.
FIG. 2 is a flowchart describing the sequence of operations implemented by the
system of FIG. 1 according to a first embodiment disclosed herein. The operational
sequence of FIG. 2 is p~lrolllled when the system of FIG. 1 is to be employed inconjunction with a telephonic device that operates using a power source 113. Theprogram commences at block 301. At block 303, a test is pcl~,llled to ascertain whether
or not the tip/ring line 121 (FIG. 1) and a power source 113 (FIG. 1) are both connected
to the automatic dialing mode selection system 100 (FIG. 1). In this context, a tip/ring
line 121 "connection" means that one end of the tip/ring line 121 is connected to the
automatic dialing mode selection system 100 and the other end of the tip/ring line 121 is
connected to an active communications port at the public switched telephone network
(PSTN), with electrical coupling between the PSTN and the automatic dialing mode
Io 2 1 867q4
selection system 100. Such a connection signifies that tip/ring line 121 has been activated
and placed into service by the PSTN, and that no discontinllities or shorts exist between
the PSTN and the automatic dialing mode selection system 100.
The PSTN applies a DC voltage potential of approximately 48 VDC across
s activated tip/ring lines when all devices connected to that tip/ring line are on-hook and the
tip/ring line is not receiving a ring signal from an incoming call. This DC voltage
potential may be l1tili~1 to power the automatic dialing mode selection system 100 in a
standby mode, so long as the current drain of this system is sufficiently low so as not to
be interpreted as an off-hook condition by the PSTN. This requirement is easily achieved
10 through the use of CMOS semiconductor devices in automatic dialing mode selection
system 100.
An ID bit is used to specify whether or not the dialing mode needs to be set. This
ID bit could be stored, for example, in a memory register of the microcontroller, a
memory device coupled to the microcontroller, a flip-flop, a latch circuit, or the like. For
purposes of illustration, an ID bit value of "1" may be defined as specifying that the
dialing mode has been set. If the dialing mode has been established, and the tip/ring line
121 remains connected to the automatic dialing mode selection system 100, the value of
the ID bit remains set at 1. An ID bit value of "0" may be defined as specifying that the
dialing mode needs to be set. Note that, if the tip/ring line 121 remains connected to the
20 automatic dialing mode selection system, the value of the ID bit is retained. If tip/ring
line 121 does not remain connected to automatic dialing mode selection system 100, the
value of the ID bit is reset to "0".
If either the power source 113 or the tip/ring line 121 are not connected to system
100, the negative branch from block 303 leads back to block 301 where the program waits
25 until both of the aforementioned connections are made. Likewise, if neither the power
source 113 nor the tip/ring line 121 are connected to automatic dialing mode selection
system 100, the program waits until both connections are made.
11 2 1 86 794
Program control progresses to block 305 where the microcontroller 115 (FIG. 1)
activates the line switch 105 (FIG. 1) to place the system 100 into an off-hook condition.
After automatic dialing mode selection system 100 is placed into an off-hook condition at
block 305, program control progresses to block 307 where the microcontroller 115 (FIG.
5 1) activates DTMF tone generator 109 (FIG. 1) to dial a DTMF digit. In a PBX
en~iro~ .ent, note that system 100 could be programmed to select the dialing mode of the
PBX itself or, alternatively, system 100 could be programmed to select the dialing mode
of the outgoing telephone line connecting the PBX to the PSTN. In the case where the
dialing mode of the outgoing telephone line is to be determined, a DTMF digit of 9 is
o dialed at block 307, followed by the dialing of a second DTMF digit. This ensures proper
operation in a PBX environment where a DTMF digit of 9 causes the PBX to access an
outgoing line to the PSTN. If a particular PBX system uses a digit or digits other than 9
to access the PSTN, then the DTMF tone generator 109 should dial such access digits.
Hereinafter, it will be assumed that the DTMF digit "9" is used to provide PSTN access
from a PBX, it being understood that a digit or digits other than 9 could also be employed
for this purpose.
After a DTMF digit is dialed (block 307), the dial tone detector 107 (FIG. 1)
checks the tip/ring line 121 for the presence of dial tone (FIG. 2, block 309). If dial tone
is present, program control jumps ahead to block 311, where the microcontroller 115 is
20 set to implement pulsed dial signaling. This function may be performed by setting a
mode bit to a value signifying pulsed dial signaling. Such a mode bit could be stored, for
example, in a memory register of the microcontroller, a memory device coupled to the
microcontroller, a flip-flop, a latch circuit, or the like. For purposes of illustration, a
mode bit value of "1" may be defined as specifying pulsed dial si~lin~, and a mode bit
25 value of "0" may be defined as specifying touch-tone dial si~ling If dial tone is absent
at block 309, the program advances to block 315 where the microcontroller is set to
implement touch-tone dial sign~ling by setting the mode bit to the a~r~liate value.
- ~ 12 2 1 86794
After block 311 or, alternatively, block 315, is pelro~ ed, program control passes
to block 313, where the microcontroller sets the ID bit to indicate that the dial si~ling
mode, i.e., the dialing mode, has been set. After the ID bit has been set, the
microcontroller continlle~ to use the mode bit to determine the dialing mode that is to be
5 employed (block 316). From time to time, the microcontroller monitors the ID bit (block
317) to determine whether or not the tip/ring line 121 (FIG. 1) remains connected to the
automatic dialing mode selection system 100 (FIG. 1). If the tip/ring line 121 remains
connected to the automatic dialing mode selection system 100, the system retains the dial
sign~lin~ mode previously determined at block 311 or block 315, and the program loops
o back to block 316. If the tip/ring line 121 is disconnected from automatic dialing mode
selection system 100, the ID bit is reset to "0", and the program loops back to block 303
and waits until the system is connected to power source 113 and tip/ring line 121.
In a PBX environment, prior to the time that PSTN access digits, such as a DTMF
"9", are dialed, no connection exists between the PSTN and the automatic dialing mode
selection system 100. If the digit 9 (or other digits providing PSTN access) are dialed at
block 307, an automatic dialing mode selection system 100 connected to an office PBX
forms a communications link with the PSTN after the dialing of the access digit(s), i.e.,
after the "9" is dialed. At this time, the PSTN will automatically apply a dial tone to the
automatic dialing mode selection system 100 which replaces the dial tone generated by
20 the PBX. The automatic dialing mode selection system 100 now proceeds to select an
appr~.;ate dialing mode using the same procedure as in the case where no PBX is
employed. In this manner, the dialing mode selection is not based upon the
"reappearance" of dial tone caused by the PBX connecting system 100 to the PSTN.Rather, dialing mode selection is properly based upon the dialing mode capabilities of the
25 tip/ring line between the PSTN and the PBX. This situation can be addressed by
pro~.. ;.. g microcontroller 115 and/or by instructing the user to dial a DTMF "9"
followed by the entry of at least one additional DTM~ digit.
13 2 1 86794
The scenario in the preceding paragraph addresses various problems presented by
a PBX environment. However, this scenario is not intended to imply that the procedure
of FIG. 2 is applicable only in a PBX environment. Note that the procedure of FIG. 2 is
applicable to environments which do not include a PBX, as in the situation where a
5 telephonic device is connected to a tip/ring line providing a direct co"l~"ications link to
the PSTN. In systems having such direct links, any DTMF digit (including 9) could be
dialed at block 307.
It is possible to automatically change the dialing mode from pulse to touch-toneafter the last digit of a telephone number has been pulse-dialed. For exarnple, such a
o technique is disclosed in U.S. Patent No. 5,369,697 which issued to Murray et al. on
November 29, 1994. Although somewhat useful in situations where an interactive touch-
tone service must be accessed from a telephone line equipped to receive only pulsed
dialing signals, this approach presents some serious shortcomings. All outgoing calls are
placed using pulse dialing and, after the call has been dialed, the dialing mode is changed
to touch-tone signaling for the duration of the call. The mode is switched from pulse to
touch-tone when the calling telephone receives ring back signals, DTMF signals, voice,
or data.- This technique presents a shortcoming in that the actual dial sipn~lin~
capabilities of the tip-ring line are not determined. Rather, it is assumed that the
telephonic device user is connected to a tip-ring line equipped to support pulsed dialing
only. Although the technique allows access to on-line touchtone services, the telephone
call is always established using relatively slow, inefficient pulse (li~ling.
In the embodiments of FIGS. 1 and 2, microcontroller 115 may be programmed
such that, in response to user input (i.e., a predetermined DTMF key press sequence), the
microcontroller will set the dialing mode bit from pulsed dialing to touch-tone dialing
2s after the call has been completed, but only for the duration of the call. In this manner, the
user can access interactive touch-tone services from a tiptring line equipped to support
only pulsed dial sign~ling for the purpose of completing an outgoing telephone call. Even
14 21 86794
though such pulsed telephone lines do not support touch-tone dial sign~lin~ for purposes
of call establi~hment after the call has been established on such a line using pulsed
sign~lin~, the line can be used to communicate DTMF signals among telephonic devices
connected to the line.
FIG. 3 is flowchart describing a sequence of operations implemented by the
automatic dialing mode selection system 100 of FIG. 1 according to a second
embodiment disclosed herein. The sequence of operations described in connection with
FIG. 3 are implemented in the operational environment of a conventional POTS
telephone. The program commences at block 401. At block 403, the POTS telephone is
o connected to a tip/ring line 121 (FIG. 1). In this context, a tip/ring line 121 "connection"
means that one end of the tip/ring line 121 is connected to the automatic dialing mode
selection system 100 and the other end of the tip/ring line 121 is connected to an active
co",."~ ications port at the public switched telephone network (PSTN), with electrical
coupling between the PSTN and the automatic dialing mode selection system 100.
The program advances to block 404. When the voltage on the first input terminal
151 of the power supply control circuit 126 rises above a pre~letçrrnined threshold,
voltage sensing circuit 135 resets latch circuit 148 with an "ID bit" value of 0, signifying
that the dialing mode has not yet been determined. The program then waits until the
POTS user places the POTS telephone off-hook. At block 407, the POTS user places the
20 POTS telephone in an off-hook condition, and dials the telephone (i.e., enters digits) to
place a call to any telephone number. After digits are entered at block 407,
microcontroller 115 (FIG. 1) reads the ID bit to determine whether or not the dialing
mode has already been set (block 408). If so, the program advances to block 430 where
the microcontroller 115 reads the value of a mode bit stored in RAM circuit 122. The
25 value of the mode bit is set to specify either pulse dialing or touch-tone (li~ling For
example, a mode bit value of 1 may correspond to touch-tone (li~ling, and a mode bit
value of 0 may correspond to pulsed dialing. After block 430, the program advances to
2186794
"~ -
block 410, where the microcontroller 115 dials the telephone number previously entered
by the user at block 407 using the dial signaling mode determined by the value of the
mode bit. The program then jumps ahead to block 418.
The negative branch from block 408 leads to block 409, where the microcontrollers 115 activates the DTMF tone generator 109 (FIG. 1) to generate in DTMF mode the first
digit entered by the POTS user at block 407 (FIG. 3). The program progresses to block
411, at which time the dial tone detector 107 (FIG. 1) checks the tip/ring line 121 for the
presence of dial tone. If dial tone is present, the program advances to block 415 where
microcontroller 115 (FIG. 1) loads RAM circuit 122 with a "mode bit" value specifying
pulsed dialing for the POTS telephone, thereby setting the dialing mode to pulse. The
program then advances to block 416 where the microcontroller 115 pulse dials the first
digit of the telephone number previously entered by the user at block 407, and the
program progresses to block 417. If dial tone is not present at block 411, the program
advances to block 413 where microcontroller 115 (FIG. 1) loads RAM circuit 122 with a
"mode bit" value specifying touch-tone (DTMF) dialing for the POTS telephone, thereby
setting the dial si~ling mode to touch-tone. As stated above, this "mode bit" is stored
as a one-bit value in RAM circuit 122.
After block 413 is performed, program control progresses to block 417. Program
control also progresses to block 417 from block 416. At block 417, the microcontroller
115 sets the "ID bit" to a value of 1, to signify that the dialing mode has been set. This
"ID bit" is stored as a one-bit value in latch 148. At block 418, the microcontroller 115
contimles to dial the telephone number previously entered by the user at block 407. This
number is dialed using the a~l~liate dial sign~ling mode as specified by the mode bit.
The microcontroller 115 continues to use the mode bit to determine pulse or touch-tone
dial si~ ng mode (block 419) for any numbers entered by the user. The
microcontroller 115 then monitors the ID bit at the output of latch 148 (block 420). If the
voltage on the first input terminal 151 of the power supply control circuit 126 falls below
21 86794
~ 16
a pre~eterrnined threshold, voltage sense circuit 135 resets the latch 148, signifying that
the POTS telephone has been removed from the tip/ring line 121, and/or that tip/ring line
121 is no longer active. If the latch has been reset, execution of the program is suspended
(block 420) until the voltage on the first input terminal 151 once again exceeds a
5 pre~letPrmined threshold, whereupon the program then loops back to block 403. If the
latch has not been reset, the program loops back to block 419.
