Cellular telephone signalling circuit operable with different cellular telephone systems

Apparatus operable with different cellular telephone systems and signalling protocols is described. Signalling messages, both data messages and supervisory related signals between a cellular telephone microcontroller (4) and a base station are transferred via a baseband signalling circuit (10). The baseband signalling circuit is operable to employ different signalling protocols, the protocol being selected by control bits provided from the microcontroller to the signalling circuit. In a preferred embodiment, the signalling protocol selection is made between an AMPS/TACS signalling protocol and a NAMPS/NTACS subaudible signalling protocol.

FIELD OF THE INVENTION 
This invention relates generally to cellular telephone signalling protocols 
and, more particularly, to dual-mode or multi-mode cellular telephones 
capable of changing a signalling protocol according to a mode selection so 
as to operate with different cellular telephone systems. 
BACKGROUND OF THE INVENTION 
FIG. 1 is a simplified block diagram showing a signalling path of a 
cellular telephone. An antenna 1 is coupled to a radio frequency (RF) 
block 2. Antenna 1 both receives and transmits RF signals for 
accomplishing a telephone conversation. A Baseband Signaling Circuit (BSC) 
3 is interposed between the RF block 2 and a controller, typically 
implemented as a microprocessor based controller (microcontroller) 4. BSC 
3 outputs an analog signal (Tx) 2a to the RF block 2, Tx 2a being used to 
modulate a suitable RF carrier. BSC 3 receives an analog signal (Rx) 2b. 
Rx 2b represents a demodulated RF signal that is received by antenna 1. 
Communication between BSC 3 and the microcontroller 4 is by digital data, 
including an Interrupt signal line 3a, an address bus 4a, and a data bus 
4b. In operation, the BSC 3 and the microcontroller 4 implement a selected 
signalling protocol when transmitting and receiving a telephone 
communication. 
A conventional Advanced Mobile Phone Services (AMPS), and also a Total 
Access Communication System (TACS), signalling protocol and format is 
described in Appendix A of the Specification. 
As described in Appendix A and FIG. 7, for a Forward Control Channel (FCC 
or FOCC) and a Reverse Control Channel (RCC or RECC) signalling protocol, 
the FOCC signalling is a continuous bit stream from a base station (or 
land station) to a mobile station. Forward and Reverse Voice Channel (FVC 
and RVC) signalling protocols are employed for voice channels (or speech 
channels). The FVC and the RVC are both burst type messages; that is, not 
a continuous bit stream. 
Referring to FIG. 8, a Supervisory Audio Tone (SAT) and a Signalling Tone 
(ST) are used on the voice channel, SAT being a continuous signal from 
base station to mobile station, with the mobile station transponding the 
SAT back to the base station. The ST is a burst type signal from the 
mobile station to the base station. 
At present, mobile telephones are not available that are operable on both 
the AMPS and the TACS systems. Thus, if a mobile telephone is constructed 
or programmed to be an AMPS telephone, it cannot be user-selected to 
operate also on TACS. But, the same signaling circuit can be used in both 
types (AMPS/TACS) telephones, and the selection of the signalling circuit 
may occur at initialization. 
The AMPS/TACS selection of the signaling circuit can be achieved by 
changing the bit rate. The frame structure (both control and voice 
channel), and the supervisory signals (SAT and ST), are identical for both 
systems. 
However, narrow band AMPS (NAMPS) and narrow band TACS (NTACS) present 
clearly different signaling protocols. A subaudible signalling protocol is 
employed on NAMPS voice channels. NAMPS voice channels are referred to as 
narrow band voice channels, because the channel spacing is substantially 
smaller than on an AMPS voice channel (30 Khz .fwdarw.10 Khz). 
Correspondingly similar differences exist in NTACS as compared to TACS. 
The NAMPS/NTACS system is a dual-mode system. That is, mobile telephones 
must be operable both on AMPS/TACS--specific wide band voice channels, and 
on NAMPS/NTACS--specific narrow band voice channels (utilizing subaudible 
signaling). 
The NAMPS/NTACS narrow band voice channel signalling protocol (frame) is 
shown in FIG. 3. 
Supervisory signalling on the voice channel is realized by DSAT and DST. On 
voice channel mobile receivers there is utilized a continuous bit stream, 
Digital SAT (DSAT) 200 bit/s, NRZ-coded, which is also transponded to the 
base station. There may be up to seven different DSAT patterns. 
Furthermore, ST is a Digital ST (DST), also 200 bits/s, NRZ. The DST signal 
is generated by inverting the transmitted DSAT. 
Voice channel signalling is accomplished by a digital DATA WORD, which is 
100 bit/s, Manchester coded. The DATA WORD does not contain repeats, as on 
AMPS and TACS (control and voice channels), but only one data message. The 
DATA WORD is preceded by a Word Sync pattern (WSYNC) which is a fixed 
30-bit pattern, 200 bit/s, NRZ. 
DSAT is a continuous bit stream, which can be replaced by WSYNC and DATA 
WORD for certain periods of time. Thus, the DATA WORD is not a burst type 
of transmission having its own frequency, but is instead "embedded" in the 
DSAT pattern. 
Based on the foregoing, required NAMPS signalling functions for a mobile 
station include the following: 
a) detecting received DSAT (NRZ) and transponding DSAT to the base station; 
b) detecting WSYNC (NRZ) and DATA WORD, Manchester-decoding DATA WORD, and 
also BCH-decoding DATA WORD; 
c) transmitting DST (NRZ) (invert transmitted DSAT); and 
d) transmitting WSYNC (NRZ) and DATA WORD, DATA Manchester and BCH-coded. 
As a result, several problems must be overcome to realize NAMPS signalling 
in a mobile station, as compared to an AMPS signalling embodiment. These 
problems include the following. 
a) The bit rate is substantially different, i.e., significantly slower. 
b) DSAT, DST and WSYNC are not Manchester-coded, but DATA WORD is, although 
all of these signals appear in the same continuous bit stream. Thus, DATA 
WORD must be encoded (transmitter) and decoded (receiver), but DSAT and 
WSYNC not encoded (transmitter) or decoded (receiver). 
c) DATA WORD does not contain repeats. As a result, AMPS 3/5 majority 
voting is not required. 
d) DATA WORD is "embedded" in the DSAT bit stream, and occasionally 
replaces the DSAT bit stream. 
e) WSYNC has a different length (30 bits instead of 11 bits as found in 
AMPS). 
f) Also, there are seven different DSAT patterns, instead of the three SAT 
patterns. 
One known implementation of NAMPS narrow band voice channel signalling 
includes a conventional AMPS (TACS) signalling circuit, and also 
additional circuitry to accomplish NAMPS signalling, to and from the 
microcontroller 4 or some other controller. This approach also requires a 
substantial amount of additional software for the microcontroller 4. 
By example, this technique can be realized by using a commercial 
AMPS-signalling circuit, such as the DPROC/UMA 1000, available from 
Philips/Signetics, for AMPS signalling, and also an additional circuit, by 
example a NE5234, a switch, and a microcontroller (PCB80C552) to 
accomplish narrow band NAMPS signaling. 
However, this approach requires additional components, which increases at 
least component cost and also power consumption. Depending on the amount 
of additional circuitry to implement NAMPS, a substantial amount of 
additional software may also be required. Also, surface area requirements 
on printed circuit boards is increased, thus making it more difficult to 
implement a small, lightweight portable telephone. 
It can thus be realized that what is required is a signalling circuit that 
is both area and cost effective, consumes no additional current, has an 
efficient interface to microcontroller software, and is operable on both 
AMPS/TACS and NAMPS/NTACS signalling systems. 
OBJECTS OF THE INVENTION 
Accordingly, it is an object of this invention to provide a signalling 
circuit operable with different cellular telephone systems and with 
different signalling protocols. 
It is another object of this invention to provide a signalling circuit 
operable with AMPS/TACS control and voice channels, and also with 
NAMPS/NTACS channels, with the operational mode and function of the 
circuit being selected by one or more control signals. 
It is another object of this invention to provide a signalling circuit 
which has a flexible interface to a microcontroller, so that the interface 
data bus bit rate, bus width, and interrupt rate may be modified during 
operation. 
It is a further object of this invention to provide a signalling circuit 
that enables control of transmitted modulated signal deviation, by control 
signals from a microcontroller to the signalling circuit, on all systems 
and on both wide band and narrow band voice channels. 
SUMMARY OF THE INVENTION 
The invention provides a baseband signalling circuit for use with a 
cellular telephone, the baseband signalling circuit including an interface 
to a cellular telephone controller and an interface to a radio frequency 
reception and transmission circuit. The baseband signalling circuit is 
responsive to a first state of a control signal line for operating in 
accordance with wideband AMPS/TACS signalling protocols (greater than one 
kilo-Hertz), and is also responsive to a second state of the control 
signal line for operating in accordance with narrowband NAMPS/NTACS 
subaudible signalling protocols (less than one kilo-Hertz). The state of 
the control signal line is controlled by the cellular telephone 
controller. 
The first interface includes a multi-bit data bus and an interrupt signal 
line that is coupled between the baseband signalling circuit and the 
cellular telephone controller. The baseband signalling circuit is 
responsive to information written over the data bus by the cellular 
telephone controller for selectively generating the interrupt signal on an 
occurrence of a reception of eight data bits from the second interface, or 
on an occurrence of a reception of one bit from the second interface. 
A decoder is responsive to the first state of the control signal line for 
operating as a Manchester decoder for decoding AMPS/TACS data that is 
received from the second interface. The decoder is also responsive to the 
second state of the control signal line for operating as a one bit 
integrator for decoding NAMPS/NTACS DSAT, WSYNC, and DATA WORD information 
that is received from the second interface. 
When operating in the narrowband mode, the control signal line is also 
employed to place wideband circuitry into a low power quiescent state, 
thereby reducing power consumption.

DETAILED DESCRIPTION OF THE INVENTION 
An example of a baseband signalling circuit 10 is shown in block diagram 
form in FIGS. 2a and 2b. The illustrated circuit operates only with 
AMPS/TACS control and voice channels. 
A Control Register (CREG) 12 includes 8-bit registers for controlling 
circuit operation. Internal clocks are generated from a 4.8 Mhz clock in 
block CLOCKDIV 14. 
An input node (DI) 16 provides an output to a low-pass filter (AAFIL) 18 
which attenuates high input frequencies to prevent aliasing in subsequent 
switched capacitor (SC) filter stages. AAFIL 18 has a 6 dB passband gain. 
The data is connected through a comparator (DATACOMP) 20 to a Manchester 
decoder (MANDEC) 22 which decodes the Manchester encoded data to a NRZ 
(Non-Return to Zero) format. 
The signalling circuit 10 is synchronized to the received data with a 
digital Phase Locked Loop (DPLL) 24 and with a word synchronization 
detection logic block (RECBUF) 26. 
Data validity (block DATVAL 28) is continuously monitored (status flag 
DFLAG), and this information is used internally by the circuit 10. 
The serial data from the Manchester decoder 22 is 3/5 majority voted in 
block VOTE 30, Bose-Chandhuri-Hocquenghem (BCH) decoded in block 32, 
corrected (CORR) in block 34, and shifted into a receiver register (RREG) 
36. A final data word is comprised of 28 bits. Four status bits are added 
to RREG 36 to make up a 32-bit register, which is read by microcontroller 
4 in 8-bit increments (bytes), via status multiplexer (SMUX) 38 (FIG. 2b). 
The generator polynomial for a (40, 28; 5) BCH code is: 
EQU gB(x)=X.sup.12 +X.sup.10 +X.sup.8 +X.sup.5 +X.sup.4 +X.sup.3 +X.sup.0. 
The code, a shortened version of the primitive (63, 51; 5) BCH code, is a 
systematic linear block code with the leading bit as the most signficant 
information bit and the least-significant bit as the last parity-check. 
SMUX 38 outputs (a) the receiver data registers, (b) test registers (not 
shown), or (c) the status register to an 8-bit data bus provided at 
interface 40. The microcontroller 4 is connected to the 8-bit data bus for 
receiving the information output by SMUX 38. 
Referring again to FIG. 2a, a Receiver timing block (RECTIM) 42 extracts 
the data from received frames on both control and voice channels and 
generates data transfer interrupts (WFLAG) and repeat interrupts (RFLAG). 
RECTIM 42 also separates the time multiplexed data streams (channel A and 
B) and Busy/Idle-information (XBOI) on the control channel. RECTIM 42 also 
maintains bit and word synchronization during different frames, and passes 
a synchronization status (SFLAG) forward to the status register. 
The Supervisory Audio Tone (SAT) signal is filtered and amplified with a 
band-pass filter (SATFIL) 44. The output of SATFIL 44 is converted to a 
digital square wave signal by block SATCOMP 46. 
SAT detection is done with a digital PLL/detection circuit (SATDET) 48. 
This logic compares the SCC code given by control register 12 bits SCC0 
and SCC1 to the incoming SAT frequency and indicates the result with a 
status register bit (SATVAL). The regenerated SAT is then fed to block 
DACSUM 50 for transmission. Data to be transmitted is loaded into a 
transmitter register (TR) 52. From the TR 52 the data is converted to 
serial form, serially shifted to a Manchester encoder (MANENC) 54, and 
then inputted to DACSUM 50. 
The sending of ST is controlled with a control register bit STE that is fed 
to DACSUM 50. 
DACSUM 50 generates the analog output signals (ST, SAT and wide band data) 
from the digital inputs, and sums them to create an analog signal to be 
transmitted (TX). The analog signal is low-pass filtered at block TRFIL 
56. 
A Post-Filter (POSTFIL) 58 attenuates the clock frequency noise in the 
output signals. The output of POSTFIL 58 is connected to output pin DO 60 
and is provided to the RF block 2 (FIG. 1). 
The Interface 40 includes Address signal lines (A0, A1) and a Select signal 
line (XCS) whereby the microcontroller 4 can select specific ones of the 
circuit 10 registers. The Interface 40 also includes a Read Strobe (XRD) 
and a Write Strobe (XWR), in addition to the Interrupt signal line (INT). 
These various Interface signal lines operate, in conjunction with the 
eight bit data bus (D0-D7), in a conventional fashion, and allow the 
microcontroller 4 access to the internal registers of the circuit 10. 
One significant difference between the AMPS and the TACS protocols is the 
signalling bit rate. On AMPS the signalling bit rate is ten kbit/s, and on 
TACS the signalling bit rate is eight kbit/s. Selection is made by one 
control bit in CREG 12, by changing clock division in CLOCKDIV 14 to 
change the output clocks to other blocks and, thus, consequently the 
operational frequency of the other blocks. 
According to the present invention, the above-described AMPS/TACS 
signalling circuit shown in FIGS. 2a and 2b is modified to be operable 
also with NAMPS/NTACS narrow band voice channels, and to thus operate also 
with subaudible signalling. Generally, the signalling circuit of FIGS. 2a 
and 2b is reconstructed so that it can receive and transmit a 200 bit/s 
data stream, to have a flexible interface to the microcontroller, and to 
have the microcontroller 4 interpret the data contents. 
Significantly, the reconstructed circuit does not use the SAT signal blocks 
(SAT signal path) to receive the Digital SAT (DSAT), but instead employs 
the data signal path to receive (and transmit) both DSAT and data messages 
(data messages: WSYNC+DATA WORD). 
FIGS. 4A and 4B are a block diagram of a presently preferred embodiment of 
the signalling circuit 10'. Signal paths employed for subaudible signaling 
are marked with a broken line, and blocks that function for AMPS/TACS 
operation as in FIGS. 2a and 2b are similarly numbered. 
CREG 12 includes one additional 8-bit control register REG 12a for 
controlling the circuit 10' in the NAMPS/NTACS mode. The mode of operation 
is selected by a control bit (NOXW) in control register 12a. Control bit 
NOXW is distributed throughout the circuit 10' and influences the 
operation of most of the blocks, changing the operation from wide band 
signaling to narrow band signaling. The following table shows the contents 
of the control register REG 12a: 
______________________________________ 
Bit 
Position Name Description 
______________________________________ 
D(n) NOXW Narrow band or Wide 
band of selection 
D(n + 1) ISEL80X1 Interrupt interval selection 
(1 or 8 bits) 
D(n + 2) BWRGE1 Bandwidth range selection 
for DPLL 24 
D(n + 3) BWRGE2 Bandwidth range selection 
for DPLL 24 
D(n + 4) DTX Discontinuous transmission 
selection 
______________________________________ 
The operation of Control bits ISEL8OX1, BWRGE1, BWRGE2 and DTX is described 
in detail below. 
It should be noted that control bit NOXW changes the CLOCKDIV 14 divisions 
so that the CLOCKDIV output clocks are of a reduced frequency, thus 
changing the operational frequency of the circuit 10' from the AMPS/TACS 
10/8 kHz range to the NAMPS/NTACS 200 Hz range. 
RECEIVING of Subaudible Signalling 
The incoming NAMPS/NTACS signal (RX) appearing at node DIN 16 is first low 
pass filtered in block AAFIL 18. In the NAMPS/NTACS narrow band mode the 
AAFIL 18 has a 12 dB passband gain, as opposed to 6 dB in the AMPS/TACS 
embodiment of FIG. 2. NRECFIL 62 functions as a 100 Hz low pass filter, 
filtering out the incoming voice signal and noise. The operation of 
NRECFIL 62 is described in greater detail in commonly assigned U.S. patent 
application Ser. No. 07/893,752, filed on even date herewith, entitled "A 
Switched Capacitor Decimator", by J. Pikkarainen now U.S. Pat. No. 
5,289,059, issued Feb. 22, 1994. 
The data is converted to digital form in DATACOMP 20, as in the wideband 
mode. The data is applied to DPLL 24 where the data is synchronized to the 
internal digital clock. DPLL 24 is employed to generate a bit rate clock 
to clock the data, and also to clock all receiver blocks. The nominal DPLL 
24 center frequency in wide band mode is 10/8 kHz, and is changed by the 
control signal NOXW to 200 Hz in the narrow band NAMPS/NTACS mode. 
Additionally, in the narrow band mode, the CREG 12 bits BWRGE1 and BWRGE2 
are used to select the bandwidth (locking range around the center 
frequency) of the DPLL 24 according to the following table (Fc=nominal 
center frequency). 
______________________________________ 
NAMPS NTACS 
BWRGE2 BWRGE1 bandwidth bandwidth 
______________________________________ 
0 0 Fc +/- 1.56 Hz 
FC +/- 1.56 Hz 
0 1 Fc +/- 3.125 Hz 
FC +/- 3.125 Hz 
1 0 Fc +/- 6.25 Hz 
FC +/- 6.25 Hz 
1 1 Fc +/- 12.5 Hz 
FC +/- 12.5 Hz 
______________________________________ 
From the DPLL 24 the synchronized 200 bit/s data stream is input to the 
MANDEC 22. The MANDEC 22 is used as a Manchester Decoder in the wide band 
mode, but in the narrow band mode is operated instead as a bit integrator. 
The MANDEC 22 obtains several samples from each received bit (symbol) and 
determines whether a zero or a one bit is received. The function of the 
integration is to minimize the effect of noise and distortion in the 
received data. Also, the effect of jitter in the data can be minimized, 
for example, by handling the samples in the mid-area of the bit in a 
different manner (weighing factors) as compared to samples on side areas 
of the bit. 
More specifically, in the wide band mode the MANDEC 22 converts the 
Manchester coded data to NRZ data by integrating the ex-or of the 
Manchester coded data (RECDXQ) and the clock generated by the DPLL 24 
(QREC) over one QREC period (from one rising edge of QREC to the next). 
The integration is accomplished by sampling the ex-or output at a rate of 
320 kHz for TACS and 400 Khz for AMPS, which yields 40 samples per bit 
period. An internal six bit counter counts the number of samples wherein 
the ex-or output is high. A count of 20 or greater results in a one at the 
output (DREC). A count of less than 20 results in zero. The converted NRZ 
data is available at the DREC output during the QREC period following the 
decoded period. 
In the narrow band mode Manchester decoding is inhibited. All incoming bits 
are treated as NRZ bits having a baud rate of 200 bits/s. A logic one at 
input RECDXQ enables the six bit counter to count. The sampling rate is 8 
kHz, i.e. 40 samples per bit period. In the narrow band mode a weighting 
function specifies increments of the integrator counter, as seen in FIG. 
6. More specifically, FIG. 6 illustrates a weighting function h(n) of 
integration wherein: 
h(n)=0, when n=1,2,3,4,5,6,7,34,35,36,37,38,39,40; 
h(n)=1, when n=8,9,10,11,12,13,28,29,30,31,32,33; and 
h(n)=2, when n=14,15,16,17,18,19,20,21,22,23,24, 25,26,27. 
A decided data bit y(k) is given by: 
##EQU1## 
where x is a sample of the input data. 
It should be noted that all received data, including DSAT, WSYNC, and DATA 
WORD, is processed in similar manner; as a 200 bit/s bit stream. That is, 
although the DATA WORD is 100 bit/s Manchester coded, and DSAT and WSYNC 
are each 200 bit/s NRZ coded, the 100 bit/s Manchester coded data may be 
interpreted also as 200 symbols/s data. FIG. 5 shows a clarifying example 
of this technique. All bit streams in the MANDEC 22, and also in 
subsequent blocks, are processed as a 200 bit/s stream. At the 
microcontroller 4, the bit streams are interpreted differently, as will be 
described. 
RREG 36, which is used in the wide band mode to buffer the received (and 
3/5 voted and BCH-decoded) data word as 28 bits+additional status bits, is 
also used as a data buffer in the narrow band mode. The 200 bit/s bit 
stream (DSAT, WSYNC or DATA WORD) from MANDEC 22 is directly shifted to 
RREG 36 without any further processing. From RREG 36 the received data 
bits are output to the microcontroller 4 for interpretation, after the 
generation of an interrupt by RECTIM 42. 
RECBUF 26, which is used in the wide band mode to detect the 11-bit 
synchronization pattern, is not used in the narrow band mode, i.e. the 
output status bit (WS, or WSYNC, in FIG. 2) is ignored. If desired, RECBUF 
26 may be used to detect the 30-bit NAMPS/NTACS WSYNC pattern, by 
providing a suitable buffer length (1-30 bits) and appropriate detection 
logic. 
DATVAL 28, which is used in the wide band mode to detect if data is being 
received, is also not used in the narrow band mode, i.e. the output status 
bit (DFLAG in FIG. 2) is ignored. However, this function also may be used, 
if desired, with the 200 bit/s stream to detect the quality of the 
received signal. 
Blocks VOTE 30, BCH 32 and CORR 34, which are used in the wide band mode to 
3/5 majority vote the received data repeats and to BCH-decode the data 
word, are also not used in the narrow band mode. In the narrow band 
signalling protocol there are no repeats, thus the VOTE block 30 is not 
required. Blocks BCH 32 and CORR 34 could be employed to BCH-decode the 
DATA WORD, thereby performing this function with the signalling circuit 
10', instead of the microcontroller 4. 
Also, the SAT detection signal path (SATFIL 44, SATCOMP 46, SATDET 48) is 
not used in the narrow band mode, and is preferably set by the control 
signal NOXW to a stand-by mode of operation to reduce current consumption. 
The microcontroller 4, which receives the data via SMUX 38 and Interface 
40, uses several interrupt and status flags when receiving wide band 
(AMPS/TACS) channels. DFLAG is used to supervise the quality of received 
data, SFLAG is used to supervise frame synchronization, RFLAG is used to 
indicate that a new repeat has been received, and WFLAG to indicate that 
the entire word (several repeats) has been received. 
For the narrow band voice channels, only one receiving flag, for example 
WFLAG, is used to cause an interrupt and to indicate to microcontroller 4 
that it should read data from the signalling circuit 10'. Other flags, for 
example DFLAG, could also be used, although only one flag signal is 
necessary. 
The bit content of the data received by the microcontroller 4 is analyzed 
in accordance with the format shown in FIG. 3 and, if DSAT is indicated, 
the data is transponded to the transmitter. In the case of a WSYNC and a 
DATA WORD pattern, DATA WORD is Manchester-decoded and BCH-decoded in the 
microcontroller 4, and appropriate actions are taken. 
When employing the narrowband voice channels, the interrupt mechanism 
(generated in block RECTIM 42) and data transfer method from the 
signalling circuit 10' to the microcontroller 4 provides a flexible 
interface. If desired, the same method may be employed for the wideband 
channels. Preferably, an interrupt is generated with WFLAG after every 
eight bits. In response, the microcontroller 4 reads the byte from the 
RREG 36 block and the interrupt is removed. 
For the case of 200 bits/s signalling, the time to accumulate eight bits 
can be substantial (40 ms for DSAT and WSYNC, 80 ms for DATA WORD). 
However, advance information from the first received bits is required. 
Thus, a timing and interrupt modification is provided, implemented by 
control bit ISEL8OX 1. When ISEL8X1 is set to one (high), the interrupt 
interval, or cycle, is eight bits. When this bit is set to zero (low), the 
interrupt cycle is set to only one bit, and data may be read into the 
microcontroller 4 bit by bit. The interrupt cycle selection is modifiable 
during operation, so that the microcontroller 4 may select the interrupt 
cycle which is the most optimum for a given circumstance. 
For example, if DSAT is received during the normal condition (narrow band), 
an 8-bit interrupt cycle is the most convenient, as it does not require 
the microcontroller 4 to service the interrupt at a rapid rate, thereby 
releasing the microcontroller 4 for other operations. However, if, for 
example, DSAT is lost or is being tracked for the first time after setting 
the voice channel, or if there are bit errors, or if DSAT is changing to 
WSYNC and DATA WORD, or any other similar operation is occurring, the 
1-bit interrupt cycle may be the most optimum mode of operation. 
In the 1-bit interrupt cycle mode the signalling circuit 10' provides a 
mechanism to accommodate the case where the microcontroller 4, for some 
reason, cannot service every interrupt. If the bit interrupt occurs, and 
the bit is not read before the next bit is received (and a new interrupt 
occurs, or the previous interrupt flag remains active), the received bits 
are serially shifted into the 32-bit RREG 36 and stored. As a result, the 
bits may be read by the microcontroller 4 one by one, or in groups of 2, 
3, 4, . . . , or in any group up to eight bits in length (the width of the 
interface 40 data bus). 
In summary, in the receiving mode for subaudible signalling, a single 
control bit (NOXW) causes the passbands of the filter blocks to be changed 
to a value suitable for a 200 bit/s rate, the DPLL 24 center frequency is 
reduced from 10/8 kbits/s to 200 bits/s, the Manchester decoder 22 
operates as a bit integrator, and the receiver register 36 is used to 
buffer the serial data before transferring the data to microcontroller 4. 
All other functions associated with the wide band mode may be set to 
stand-by, or they may be employed to enhance the operation of the circuit 
10' by reducing the processing burden of the microcontroller 4. 
TRANSMITTING of Subaudible Signalling 
For AMPS signalling, speech is nominally modulated with a deviation of 8.0 
kHz, with a maximum deviation of up to 12 kHz. In comparison, the SAT is 
deviated by only a relatively small amount (+/-2.0 kHz). All data is sent 
at 10 kilobits per second and is modulated onto the carrier using 
Frequency Shift Keying (FSK) with a deviation of 8.0 kHz. The 10 kHz 
signalling tone (ST) is also modulated with 8.0 kHz deviation. The 
filtered wideband data stream is employed to modulate the carrier using 
direct binary FSK. A one (high) into the modulator corresponds to a 
nominal peak frequency deviation that is 8.0 kHz above the carrier 
frequency. A zero (low) into the modulator corresponds to a nominal peak 
frequency deviation that is 8.0 kHz below the carrier frequency. 
For subaudible signalling, data to be transmitted is loaded by the 
microcontroller 4 into the signalling circuit 10' transmitter register TR 
52 in 8-bit increments. From TR 52 the data is serialized (block 52a), and 
then input to the NDATA D/A converter of DACSUM 50'. In the signalling 
circuit 10', all transmitted data is processed as 200 bits/s, including 
DSAT, DST, WSYNC and DATA WORD. Thus, in that DSAT, DST and WSYNC are 
NRZ-coded, they are loaded as they are (pure bit stream) from the 
microcontroller 4 to the signalling circuit 10'. However, DATA WORD (100 
bits/s) is Manchester-coded (to be 200 symbols) in the microcontroller 4 
before being loaded into the signalling circuit 10'. 
Thus, the operation of the transmitter in the narrow band mode of operation 
is similar to the operation in the wide band mode, except for the 
following distinctions. 
The Manchester-encoder block MANEN 54 is bypassed, the bypass being 
controlled by the control bit NOXW. 
The bit rate is reduced from 10/8 kbits/s to 200 bits/s, by changing the 
clock frequency from CLOCKDIV 14 to the transmitter blocks. The clock 
change is also controlled by control bit NOXW. 
In both modes (narrow band and wide band) the data loading is timed by a 
Transmit Interrupt Flag, TFLAG. When TFLAG is high, the signalling circuit 
10' indicates that it is ready to load a new byte from microcontroller 4. 
The transmitted sub-audible analog signalling data output by the NDATA D/A 
of DACSUM 50' is filtered in a low pass filter NTRFIL 64 (bandwidth 150 
Hz) to remove the higher spectrum contents within the audio band. Block 
NPOSTFIL 66 attenuates any clock frequency noise in the output signal. The 
output of NPOSTFIL 66 is applied to the output node 60 and thus to the RF 
block 2 for transmission. 
In summary, for the subaudible signalling transmitter operation, the single 
control bit (NOXW) causes the Manchester encoder to be by-passed, the bit 
rate to be reduced to 200 bits/s, and the D/A converter and filter blocks 
passbands to be changed so as to be suitable for the 200 bits/s rate. 
In accordance with an aspect of the invention, the Control bit NOXW 
preferably sets all unnecessary signal blocks, including certain of the 
analog filter blocks, to a standby mode. This is accomplished by resetting 
these blocks, or by inhibiting their input clock signals. The current 
consumption in the narrow band mode is thus less than in the wide band 
mode (voice channel), mostly as a result of setting blocks SATDET 48 and 
DATVAL 28 in a low power mode. As can be appreciated, the reduction in 
power consumption of a mobile telephone is an important consideration, in 
that battery life is extended. 
The level of the transmitted signal, and the corresponding transmission 
deviation, are now described. 
The level of the transmitted subaudible signalling data is selected in 
block DACSUM 50', by control bits NOXW (narrow/wide band), TOXA (TACS/AMPS 
selection) and DTX (Discontinuous Transmission), all of which originate 
from CREG 12. On the NAMPS/NTACS voice channels, and during so called 
discontinuous transmission (DTX), the transmitted signal deviation at the 
antenna 1 is changed, and the transmitted power is decreased. 
Discontinous transmission refers to the ability of a mobile station to 
switch autonomously between two transmitter power level states while the 
mobile station is in a conversation state on a voice channel. 
Changing the signal deviation in the transmitter is accomplished by 
changing the analog signal level at the signalling circuit 10' output 
node, DOUT 60, according to the following criteria. 
Output levels at DOUT 60 in the wide band mode operating condition 
(NOXW=0): 
ST=2.3 Vpp 
WIDE BAND DATA=2.3 Vpp 
SAT=610 mVpp (TACS) 
SAT=575 mVpp (AMPS) 
Output levels at DOUT 60 in the narrow band mode (NOXW=1): 
NARROW BAND DATA=201 mVpp (AMPS, DTX=0) 
NARROW BAND DATA=252 mVpp (TACS, DTX=0) 
NARROW BAND DATA=804 mVpp (AMPS, DTX=1) 
NARROW BAND DATA=1004 mVpp (TACS, DTX=1) 
The output level change control within the signalling circuit 10', between 
the AMPS and TACS mode, is a useful feature. However, the level 
selections, and thus the deviation control in the NAMPS/NTACS modes, and 
even more specifically during DTX conditions, are very useful and provide 
advantages over conventional systems. 
That is, this aspect of the invention relates to a frequency deviation 
change when the channel is changed on the same system (for example from 
the AMPS voice channel to the NAMPS voice channel, or when discontinuous 
transmission is used on AMPS/TACS or NAMPS/NTACS voice channels) during 
normal operation. In other words, this aspect of the invention provides a 
method to change the transmitted frequency deviation during a telephone 
conversation. 
Furthermore, by changing only a few control bits the deviation is varied, 
thereby eliminating a need to add additional components, such as RF 
components, for level selection. This solution saves area, component 
costs, and current consumption in the telephone. 
A presently preferred specification for the transmitted signal deviation is 
as follows: 
__________________________________________________________________________ 
AMPS Data +/- 8.0 kHz SAT +/- 2.0 kHz ST +/- 8.0 kHz 
TACS Data +/- 6.4 kHz SAT +/- 1.7 kHz ST +/- 6.4 kHz 
NAMPS +/- 700 Hz (DSAT, DST, WSYNC, DATA WORD) 
NAMPS/DTX +/- 2.8 kHz (DST transmitted, instead of DSAT) 
NTACS +/- 700 Hz (DSAT, DST, WSYNC, DATA WORD) 
NTACS/DTX +/- 2.8 kHz (DST transmitted, instead of DSAT) 
__________________________________________________________________________ 
The mobile phone's transmitter is implemented in such a manner that, for 
the previously mentioned signalling circuit 10' output levels at DOUT 60, 
a specified deviation occurs in the transmitted signal. For example, in 
AMPS with a WIDE BAND DATA signal at DOUT 60, a signal level of 2.3 Vpp 
produces 8.0 kHz deviation in the transmitted signal. Correspondingly, in 
the TACS mode with a WIDE BAND DATA signal at DOUT 60, a signal level of 
2.3 Vpp will produce 6.4 kHz deviation in the transmitted signal, as 
specified above. 
According to the present invention, the AMPS/TACS signalling circuit of 
FIG. 2 is modified as in FIG. 4 to also be operable for NAMPS/NTACS 
cellular telephone systems that employ narrow band voice channels and 
subaudible signalling. The modified signalling circuit is thus enabled to 
also receive and transmit subaudible signalling protocols, in conjunction 
with the microcontroller 4. 
The embodiment of FIGS. 4A and 4B does not require a significant number of 
additional components, or more than a few additional internal blocks, and 
thus overcomes the disadvantages of described prior art technology. The 
presently preferred embodiment, through the use of a single control signal 
(NOXW), is enabled to switch between AMPS/TACS and NAMPS/NTACS signalling 
protocols and thus provides savings in cost, area, and power consumption. 
It should be understood that the foregoing description is only illustrative 
of the invention. Various alternatives and modifications can be devised by 
those skilled in the art without departing from the invention. 
Accordingly, the present invention is intended to embrace all such 
alternatives, modifications and variances which fall within the scope of 
the appended claims. 
APPENDIX A 
There are four signalling paths used in the AMPS network. 
The Forward Control Channels (FCC) and Reverse Control Channels (RCC) are 
used to set up calls and manage the mobiles on the system. They are not 
used for conversation. 
The Forward Voice Channel (FVC) and Reverse Voice Channel (RVC) are used 
for managing the calls. Data is transmitted on these channels before, 
after and during the call. The speech path is muted during the bursts of 
data to prevent annoyance to the calling parties. 
Speech, Data and Supervisory tones are transmitted over the network, each 
with particular modulation characteristics. 
A feature of the AMPS system is the use of two supervisory tones. These are 
sent over an assigned voice channel. 
The first tone is referred to as SAT (Supervisory Audio Tone) and is 
generated by the base station and transponded by the mobile to form a 
closed loop. Three SAT tones are available for indentification (5970, 6000 
& 6030 Hz). 
The second tone is called ST (Signalling Tone) and is a 10 kHz tone 
generated by the mobile when the handset is in place (on-hook), it is not 
sent when off-hook ST is sent over the voice channel until the handset is 
picked up. It is also sent for a period of 1-8 seconds at cleardown of a 
call, also for a period of 0-4 seconds if a three-way conversation is 
requested. 
3.7.1 FORWARD CONTROL CHANNEL 
The forward control channel (FOCC) is a continuous wideband data stream 
sent from the land station to the mobile station. This data stream must be 
generated at a 10 kilobit/second =0.1 bit/second rate. FIG. 3.7.1-1 
depicts the format of the FOCC data stream. 
##STR1## 
Each forward control channel consists of three discrete information 
streams, called stream A, stream B, and busy-idle stream, that are 
time-multiplexed together. Messages to mobile stations with the least 
significant bit of their mobile identification number (see 2.3.1) equal to 
`0` are sent on stream A, and those with the least-significant bit of 
their mobile identification number equal to `1` are sent on stream B. 
The busy-idle stream contains busy-idle bits, which are used to indicate 
the current status of the reverse control channel. The reverse control 
channel is busy if the busy-idle bit is equal to `0` and idle if the 
busy-idle bit is equal to `1`. A busy-idle bit is located at the beginning 
of each dotting sequence, at the beginning of each word sync sequence, at 
the beginning of the first repeat of word A, and after every 10 message 
bits thereafter. 
A 10-bit dotting sequence (1010101010) and an 11-bit word sync sequence 
(11100010010) are sent to permit mobile stations to achieve 
synchronization with the incoming data. Each word contains 40 bits, 
including parity, and is repeated five times; it is then referred to as a 
word block. For a multi-word message, the second word block and subsequent 
word blocks are formed the same as the first word block including the 
10-bit dotting and 11-bit word sync sequences. A word is formed by 
encoding 28 content bits into a (40, 28) BCH code that has a distance of 
5, (40, 28; 5). The left-most bit (i.e., earliest in time) shall be 
designated the most-significant bit. The 28 most-significant bits of the 
40-bit field shall be the content bits. 
2.7.1 REVERSE CONTROL CHANNEL--REQUIREMENT FOR 32-DIGIT DIALING OPTION 
The reverse control channel (RECC) is a wideband data stream sent from the 
mobile station to the land station. This data stream must be generated at 
a 10 kilobit/second=1 bit/second rate. FIG. 2.7.1-1 depicts the format of 
the RECC data stream. 
##STR2## 
All messages begin with the RECC seizure precursor that is composed of a 
30-bit dotting sequence (1010 . . . 010), an 11-bit word sync sequence 
(11100010010), and the coded digital color code (DCC). The 7-bit coded DCC 
is obtained by translating the received DCC. 
3.7.2 FORWARD VOICE CHANNEL 
The forward voice channel (FVC) is a wideband data stream sent by the land 
station to the mobile station. This data stream must be generated at a 10 
kilobit/second.+-.0.1 bit/second rate. FIG. 3.7.2-1 depicts the format of 
the FVC data stream. 
##STR3## 
A 37-bit dotting sequence (1010 . . . 101) and an 11-bit word sync sequence 
(11100010010) are sent to permit mobile stations to achieve 
synchronization with the incoming data, except at the first repeat of the 
word, where the 101-bit dotting sequence is used. Each word contains 40 
bits, including parity, and is repeated eleven times together with the 
37-bit dotting and 11-bit word sync sequences; it is then referred to as a 
word block. A word is formed by encoding the 28 content bits into a (40, 
28) BCH code that has a distance of 5, (40, 28; 5). The left-most bit 
(i.e., earliest in time) shall be designated the most-significant bit. The 
28 most-significant bits of the 40-bit field shall be the content bits. 
The generator polynomial is the same as that used for the forward control 
channel. 
2.7.2 REVERSE VOICE CHANNEL 
The reverse voice channel (RVC) is a wideband data stream sent from the 
mobile station to the land station. This data stream must be generated at 
a 10 kilobit/second.+-.1 bit/second rate. FIG. 2.7.2-1 depicts the format 
of the RVC data stream. 
##STR4## 
A 37-bit dotting sequence (1010 . . . 101) and an 11-bit word sync sequence 
(11100010010) are sent to permit land stations to achieve synchronization 
with the incoming data, except at the first repeat of word 1 of the 
message where a 101-bit dotting sequence is used. Each word contains 48 
bits, including parity, and is repeated five times together with the 
37-bit dotting and 11-bit word sync sequences; it is then referred to as a 
word block. For a multi-word message, the second word block is formed the 
same as the first word block including the 37-bit dotting and 11-bit word 
sync sequences. A word is formed by encoding the 36 content bits into a 
(48, 36) BCH code that has a distance of 5, (48, 36; 5). The left-most bit 
(i.e., earliest in time) shall be designated the most-significant bit. The 
36 most-significant bits of the 48-bit field shall be the content bits. 
The generator polynomial for the code is the same as for the (40,28: 5) 
code used on the forward control channel