Patent Publication Number: US-5633894-A

Title: Circuit for modulating a sinusoidal waveform signal using digital pulse shaping

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to modulating circuitry. In particular, the present invention to an electronics circuit for modulating a sinusoidal waveform signal using digital pulse shaping. 
     2. Description of the Prior Art 
     Communications systems have evolved over the years to utilize numerous modulation techniques for modulation a carrier signal. These modulation techniques range from amplitude to frequency and phase modulation. 
     The transmission of digital data over communication circuits is an important aspect of many modern electronic communication systems. These systems include computers, data processing equipment, modems and many other devices which must frequently be interconnected over existing voice grade communication facilities such as telephone lines, satellite links and the like. However, the transmission characteristics of existing voice grade communication facilities are often not suitable for the direct transmission of the signals in a form most efficiently processed by these modern electronic communication systems. For example, high frequency components of digital data signals are beyond the transmission capability of a number of existing voice grade communication facilities. Thus, there arises a need for converting the binary data signal which is most efficiently used by these electronic systems into a signal that is compatible with existing transmission systems. 
     There have been developed over the years many modulation techniques for the efficient transmission of digital data over existing transmission systems. One modulation technique for the transmission of digital data that has found wide spread acceptance is frequency shift key (FSK) wherein a number of signals, usually two when a binary system is used, having separate discrete audio frequencies compatible with the transmission are each assigned a separate, different symbol identification portion of the data signal. For example, in a mark-space data signal, the mark is assigned a first frequency while the space is assigned the second frequency. In these FSK systems the frequency of the signal to be transmitted is shifted from the first frequency to the second frequency as a function of the mark and space symbol identification in the data signal. 
     When high frequency and radio frequency signals are used to transmit digital data signals frequency shift keying is employed to shift a continuous-running carrier in frequency between two closely spaced frequencies according to the ones and zeros being transmitted with 850 hertz of shift being a typical value. The use of frequency shift keying to transmit digital data is extremely efficient and effective in the presence of large signal fading from changing propagation conditions. 
     While there are many devices in the prior art to shift a continuous-running carrier in frequency between two closely spaced frequencies, none of these prior art devices allow the user to change the two closely spaced frequencies of the continuous carrier by using a personal computer or the like. In addition, it would be very desirable to allow the user of a system for frequency shift keying a continuous-running carrier to efficiently trouble shot the system through use a personnel computer. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes some of the disadvantages of the prior art, including those mentioned above, in that it comprises an electronics circuit for frequency shift keying a continuous-running carrier, such as a sinewave, which allows the user to vary two closely spaced frequencies from a personal computer. In addition, the present invention allows the user to trouble shoot each logic element of the electronics circuit from his or her personal computer. 
     The electronics circuit of the present invention comprises a microcontroller which has stored therein the lower frequency and the offset frequency for frequency shift keying a continuous-running carrier, such as a sinewave. After the electronics circuit is powered up the microcontroller enters the MAIN program and generates control and address signals to effect a transfer of thirty two data bits representing the lower frequency from the microcontroller to a pair of eight bit RAMS. A programmed array logic device, which receives addresses from the microcontroller, decodes the addresses and then provides chip select and output enable signals to the RAMs to allow the thirty two data bits to be written into the RAMs with the write signal being provided by the microcontroller. 
     The microcontroller deasserts control of the RAMS and then provides a manual load signal to an oscillator data and control circuit to initiate a direct memory access data transfer of the thirty two data bits from the RAMs to a sixteen bit numerically controlled oscillator. The oscillator data and control circuit provides the control signals to the RAMs and the numerically controlled addressing to effect the direct memory access data transfer of the thirty two data bits representing the lower frequency from the RAMs to the oscillator. 
     After the transfer of the thirty two bits representing the lower frequency is complete, the microcontroller transfers the thirty data representing the offset frequency from the microcontroller to the RAMs. The oscillator data and control circuit then initiates and provides control signals to effect a direct memory access data transfer of the thirty two data bits representing the offset frequency from the RAMs to the numerically controlled oscillator. 
     After the center and offset frequencies are loaded into the numerically controlled oscillator, the microcontroller provides an output enable sinewave signal which enables the digital outputs of the oscillator resulting in a digitized sinewave signal at these outputs. A serial binary data stream of logic ones and zeros from an external source is also supplied to the oscillator. Whenever a data bit of the data stream is a logic zero the digitized sinewave signal provided by the oscillator has a frequency equal to the lower frequency. Similarly, whenever a data bit of the data stream is a logic one the digitized sinewave signal provided by the oscillator has a frequency equal to the lower frequency plus the offset frequency. The digitized sinewave signal is converted to an analog signal by a digital to analog converter. 
     The user of the present invention can load a new lower frequency and a new offset frequency by using a personal computer since the microcontroller has a debug program which is accessed from the personal computer. The debug program also allows the user to test and when necessary replace each logic element of the electronics circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1a-1f are an electrical schematic diagram illustrating the circuit for modulating a sinusoidal waveform signal using digital pulse shaping which constitutes the present invention; 
     FIGS. 2a-2c are a detailed electrical schematic diagram oscillator data and control circuit of FIG. 1; and 
     FIGS. 3A-3N illustrate some of the timing waveforms occurring during a direct memory access transfer of data from the RAMs of FIG. 1b to the sixteen bit numerically controlled oscillator of FIG. 1d. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1a-1f, there is shown a circuit for modulating a sinusoidal waveform signal using digital pulse shaping which is designated generally by the reference numeral 20. Circuit 20 comprises an eight bit microcontroller 22 which provides addressing and the read (RD) and write (WR) control signals for a programmed array logic device 24, as well as supplying a tri-state enable (TR1) signal to the programmed array logic device 24. Each of these control signals are, in turn, active low, that is, for example, programmed array logic device 24 will read the addresses supplied to its A0, A12, A13 and A14 address inputs whenever the read control signal provided by microcontroller 22 to the RD input of programmed array logic device 24 is asserted active low. 
     Port zero of microcontroller 22 which includes the P00-P07 outputs of microcontroller 22 provides the lower eight bits of addressing (address bits A0-A7) for the logic elements of circuit 20 as well as eight bit data words. The upper eight bits of addressing (address bits A8-A15) for the logic elements of circuit 20 are supplied by port two of microcontroller 22 which includes the P20-P27 outputs of microcontroller 22. Address bits A0-A7 are supplied to the 1D-8D inputs of an eight bit latch 26 and are then latched to the 1Q-8Q outputs of latch 26 by an active low enable control signal supplied by microcontroller 22 to the C input of microcontroller 22. 
     It should be noted that a logic one supplied to the output control input of latch 26 sets the 1Q-8Q outputs of latch 26 to a high impedance state. This feature of latch 26 is utilized whenever an oscillator data and control circuit 38 controls addressing and data transfer within circuit 20. 
     The computer software listing of Appendix A is for the software used by microcontroller 22. This software includes the files/modules set forth in the following table. 
     
                       TABLE I                                                     
______________________________________                                    
ABSACC.H      CTYPE.H       DEBUG.C                                       
EXTERN.H      FUNDEC.H      INIT.C                                        
IOADDR.H      ISR.C         MOD.C                                         
MOD.H         NCO.C         REG51.H                                       
SERIAL.C      STDIO.H       UTIL.C                                        
______________________________________                                    
 
    
     The main program listing for microcontroller 22 is set forth in the program file MOD.C of Appendix A and is entitled MAIN. 
     At lines 70 through 73 of the MAIN program microcontroller 22 is initialized. The MAIN program jumps to the 8031 INITIALIZATION MODULE (INIT.C). The subroutine INIT INTERVAL TIMER of the file INIT.C sets a timer 0 within microcontroller 22 to an eight bit auto reload mode and a timer 1 to provide a baud rate of 9600 for the serial port of microcontroller 22 which includes the serial input line RXD and the serial output line TXD. These serial lines may be used to interface microcontroller 22 with an external computer, not shown. 
     It should be noted that an oscillator 28 is included in circuit 20 to provide a clock signal having a frequency of 11.059 Mhz to microcontroller 22. 
     The INIT.C file also includes the INIT SERIAL PORT subroutine which initalizes the serial port lines RXD and TXD of microcontroller 22. A serial port interrupt and serial port reception are enabled during the INIT SERIAL PORT subroutine of the INIT.C file. The INIT 87C51 subroutine of the INIT.C file sets each port P0, P1, P2 and P3 of microcontroller 22 to an initial value of hexadecimal ff and disables all unused interrupts within microcontroller 22. 
     After microcontroller 22 is initialized the lower frequency is loaded from microcontroller 22 into a pair of 2048-Word by eight bit RAMS 30 and 32 with RAM 30 being identified as RAM --  1 in the MOD.C module and RAM 32 being identified as RAM --  2 in the MOD.C module. The lower frequency, which is 9.5 Mhz, is loaded or written into RAM 30 with two eight bit data words having all zeros and RAM 32 with an eight bit word having a hexadecimal value of 00 and an eight bit word having a hexadecimal value of 4C. The lower frequency is loaded into microcontroller 32 twice by the MOD.C module of the software of Appendix A. 
     The offset frequency is next loaded by microcontroller 22 into RAMS 30 and 32. The offset frequency , which is 1 Mhz, is loaded or written into RAM 30 with two eight bit data words having all zeros and RAM 32 with an eight bit word having a hexadecimal value of 00 and an eight bit word having a hexadecimal value 80. 
     When circuit 20 is operating in an Frequency Shift Keying mode, the frequency is centered around 10 Mhz and the frequency of the sinusoidal output waveform provided by an oscillator 32 shifts from 9.5 megahertz to 10.5 megahertz or from 10.5 megahertz to 9.5 megahertz when there is a change in logic state of the digital signal provided to a sixteen bit numerically controlled oscillator 36. 
     After the lower frequency and offset frequency are written into RAMS 30 and 32, the MAIN program enters a DIS RAM subroutine which disables microcontroller 22 from RAMS 30 and 32. Microcontroller 22 provides a logic one to the O --  CTRL input of eight bit latch 26 which sets latch 26 in a tri-state mode. An octal buffer 34 is also set in a tri-state mode by microcontroller 22 when microcontroller 22 provides a logic one to the 1G input of buffer 34 and a logic zero to the 2G input of buffer 34. 
     In a like manner, prior to the lower frequency and the offset frequency being written into RAMS 30 and 32, the MAIN program enters a ENA RAM subroutine. During this subroutine latch 26 is enabled when microprocessor provides a logic zero to the O --  CTRL input of latch 26, while buffer 34 is enabled when microcontroller 22 provides a logic zero to the 1G input of buffer 34 and a logic one to the 2G input of buffer 34. Enabling buffer 34 allows data from port P0 of microcontroller 22 to be written into RAM 32 via buffer 34. 
     Microcontroller 22 also provides a manual load signal which is supplied to an oscillator data and control circuit 38. When the MAN --  LOAD line transitions to the logic one state, oscillator data and control circuit 38 reads the lower frequency and the offset frequency data from RAMS 30 and 32 and then writes the data to oscillator 36. Oscillator data and control circuit 38 twice reads sixteen bits from RAMS 30 and 32 via respectively the lines DATA --  A(7:0) and DATA(7:0) since the lower frequency and the offset frequency each comprises 32 data bits. 
     After the logic one manual load signal is provided to oscillator data and control circuit 38, microcontroller 22 supplies an active low sinewave output enable signal to oscillator 36. This sinewave output enable signal enables the SIN0-SIN15 outputs of oscillator 36. The SIN0-SIN15 outputs of oscillator 36 when enabled provide the twelve most significant bits of the digitized sinewave signal to digital to analog converter 40. 
     The user of the present invention is allowed to change the lower frequency and the offset frequency by utilizing the file DEBUG.C which is entitled DEBUG MODULE. The software of Appendix A enters the DEBUG MODULE when a &#34;DEBUG&gt;&#34; prompt appears on a video screen connected to the external computer. For example, when the user enters the letter &#34;Q&#34; via a keyboard connected to the external computer, the computer will provide the ASCII character for &#34;Q&#34; via the serial input line RXD to microcontroller 22 causing microcontroller 22 to quit the DEBUG module. 
     The DEBUG module also allows the user of the present invention to, for example, enable octal buffer 34 by typing the letter &#34;B&#34; on the keyboard coupled to the external computer or tri-state the octal buffer 34 by typing the letter &#34;A&#34;. When the letter &#34;B&#34; is type on the keyboard, the DEBUG module enters the subroutine SETG1G2. Microcontroller 22 then provides a logic zero to the 1G input of buffer 34 and a logic one to the 2G input of buffer 34, enabling buffer 34. In a like manner, when the letter &#34;A&#34; is type on the keyboard, the DEBUG module enters the subroutine RESETG1G2. Microcontroller 22 then provides a logic one to the 1G input of buffer 34 and a logic zero to the 2G input of buffer 34, which sets the 1Y1-2Y4 outputs of buffer 34 to a tri-state mode. 
     By typing the letter &#34;D&#34;, the user can toggle the enable function for a digital to analog converter 40, that is the user can turn the output of converter 40 on or off. In a like manner, the &#34;R&#34; when entered into the keyboard allows the user to test RAM memory of RAMS 30 and 32. During the subroutine XRAM TEST microcontroller 22 writes zero, hexadecimal ff, hexadecimal aa and hexadecimal 55 into RAMS 30 and 32. Microcontroller 22 then reads these hexadecimal numbers from RAMS 30 and 32 and a comparison of each written hexadecimal number with each read hexadecimal number is made to check the reliability of RAMS 30 and 32. Each of the logic elements of circuit 20 can be tested using the DEBUG module of Appendix A. 
     The lower frequency for the sinewave signal output by oscillator 36 may set from zero hertz to sixteen megahertz which is one half of the frequency of the thirty two megahertz oscillator clock signal supplied by an oscillator 42 to oscillator 36. 
     The hexadecimal numbers 4C000000 and 08000000 which respectively represent the center and offset frequencies are determined by the following expression. ##EQU1## where F is the quadrature output frequency, N is the output of a frequency adder within oscillator 36 and FCLK is the 32 Mhz oscillator clock signal. 
     The computer program listing for programmed array logic device 24 is set forth in Appendix B and identified as the MOD.PLD module. Lines 17 through 24 of the MOD.PLD module define the inputs for programmed array logic device 24, while lines 27 through 30 of the MOD.PLD module define the outputs for programmed array logic device 24. 
     The logic equation for providing a chip select signal to RAM 30 is set forth at line 34 of the MOD.PLD module. The logic equation for providing a chip select signal to RAM 32 is set forth at line 35 of the MOD.PLD module. The logic equation for providing an output enable signal to RAMS 30 and 32 is set forth at line 36 of the MOD.PLD module. In each of these logic equations an explanation point &#34;!&#34; indicates that the function is not. 
     When, for example, a logic zero is provided to the/WR input of programmed array logic device 24, a logic zero is provided to the A11 input of device 24 and a logic zero is provided to the A12 input of device 24, programmed array logic device 24 decode these logic signals and then provides a chip select RAM one (CS --  RAM1) enable signal which is an active low signal enabling RAM 30 allowing data to be written into RAM 30 or read from RAM 30. 
     When a logic one is provided to the RD input, programmed array logic device 24 decodes this signal and then provides a logic zero RAM output enable (OE --  RAM) signal to the/OE inputs of RAMS 30 and 32. Depending upon which chip select signal is asserted, RAM --  CS1 for RAM30 or RAM --  CS2 for RAM 32, data is read from either RAM 30 or RAM 32. It should be noted that the/WE inputs to RAMS 30 and 32 must be at the logic one state for data to be read from RAMS 30 and 32. 
     For the write operation to either RAM 30 or RAM 32 the /CS input to the selected RAM 30 or 32 must be at the logic zero state, the/OE input must be at the logic zero state and the/WE input must be at the logic zero state. 
     It should also be noted that programmed array logic device 24 generates a chip select signal for the oscillator data and control circuit 38 (line 32 of Appendix A). This chip select signal is supplied through the EPM --  CS input of oscillator data and control circuit 38 to the CS of mode control and count register 44 enabling register 44. 
     At lines 39-41 of the MOD.PLD module of Appendix B, the RAM --  CS1, RAM --  CS2 and RAM --  OE outputs of microcontroller 24 are set in a tri-state mode. This occurs whenever these outputs are not asserted by programmable array logic device 24. At line 32 the output EMP --  CS of programmable array logic device 24 is enabled. 
     It should be noted that whenever the RAM --  CS1, RAM --  CS2 and RAM --  OE outputs of microcontroller 24 are set in a tristate mode, oscillator data and control circuit 38 controls the read and write functions of RAMS 30 and 32. 
     At this time it should be noted that the microcontroller 22 used in the preferred embodiment of the present invention is a Model 87C51 CMOS Single-Chip 8-Bit Microcontroller manufactured by Intel Corporation of Santa Clara, Calif.; the programmed array logic device 24 is a Model GAL20V8 High Performance E 2  -CMOS PLD manufactured by Lattice Semiconductor Corporation of Hillsboro, Oreg. and the RAMS 30 and 32 are Model IDT6116SA CMOS Static Rams (16Kx8-BIT) manufactured by Integrated Devices Technology Inc. of Santa Clara, Calif. Further, eight bit latch 26 is a Model SN54HC573 Octal D-Type Latch available from Texas Instruments of Dallas, Tex. and octal buffer 34 is a Model SN54HC241 Octal Buffer also available from Texas Instruments. 
     Referring to FIGS. 1a-1f and 2a-2c at lines 92 and 119 of the MAIN program (MOD.C module), microcontroller 22 transfers to oscillator data and control circuit 38 the hexadecimal number 0C, 08 and 02 via the DATA(7:0) lines. The hexadecimal numbers 0C, 08 and 02 are then supplied to the DATA[7..0] inputs of mode control and count register 44. The hexadecimal numbers 0C, 08 and 02 when processed by mode control and count register 44 set up the mode of operation of sixteen bit numerically controlled oscillator 36. 
     At this time it should be noted that the numerical controlled oscillator used in the preferred embodiment of the present invention is a Model HSP45106 16-Bit Numerically Controlled Oscillator manufactured by Harris Semiconductor of Melbourne, Fla. While the oscillator 36 may be set up to produce an FM, PSK, FSK or MSK modulated waveform, the following discussion is with respect to the FSK mode of operation of oscillator 36. 
     Microcontroller 22 also supplies addresses XBYTE[EPM], XBYTE[EPM+1] and XBYTE[EPM+2] to the ADDRS[3..0] inputs of mode control and count register 44 via the ADDR(15:0) lines. Logic zero write and chip select signals are also supplied to the mode control and count register 44 from microcontroller 22 to effect the transfer of the hexadecimal numbers 0C, 08 and 02 from microcontroller 22 to register 44 of circuit 38. 
     Mode control and count register 44 includes three registers with each register having a separate address which is defined at lines 49-55 of the REG CONTROLLER file of Appendix C. For example when the address is zero the register D0 is being written into or accessed. In a like manner, when the address is two (0010) the register D1 is being accessed and when the address is three (0011) the register D2 is being accessed. The register DO is the mode register and the registers D1 and D2 are the maximum count registers of mode control and count register 44. The maximum count registers D1 and D2 within register 44 are used in a slew mode of operation. 
     The outputs of register D0 are the MODE[7..0] outputs of mode control and count register 44, while the outputs of registers D1 and D2 are the MAX --  COUNT [10..0] outputs of mode control and count register 44. Register D1 is the lower eight bits of the eleven bit word, while register D2 is the upper three bits of the eleven bit word. The MAX COUNT [10..0] outputs of mode count and count register 44 are connected to the MAX --  COUNT [10..0] inputs of a RAM address comparator circuit 54. 
     When the present invention is operating in the FSK mode maximum count registers D1 and D2 within register 44 have hexadecimal ff written therein, that is eight logic ones are written into registers D1 and D2 within register 44. 
     Mode control and count register 44 controls the modes of operation of oscillator 36 in accordance with the following table. 
     
                       TABLE II                                                    
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       Data Bit                                                           
              Mode                                                        
______________________________________                                    
       D7     P2                                                          
       D6     P1                                                          
       D5     P0                                                          
       D4     M2                                                          
       D3     M1                                                          
       D2     M0                                                          
       D1     F0                                                          
       D0     S0                                                          
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     An eight bit (Bits D7-D0) mode control word is supplied to the mode control register 44 by microcontroller 22. The eight bit mode control words for the FSK mode of operation of oscillator 36 are the hexadecimal numbers 0C, 08 and 02. 
     Bits D7-D5 control the phase shift key (PSK) mode of operation of oscillator 36; bits D4-D2 control the DMA modes of operation of oscillator 36; bit D1 controls the BFSK mode and bit D0 controls the slew mode. 
     Microcontroller 22 first supplies the hexadecimal number 0C to the mode control and count register 44 (line 92 of the MAIN program of Appendix A). The hexadecimal number 0C has a binary value of 0,0,0,0,1,1,0,0 which in accordance with the following table is the DMA Mode Enable Center Frequency Register. 
     
                       TABLE III                                                   
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M2,M1,M0                                                                  
        Function              Load Value                                  
______________________________________                                    
0   0     0     Disabled            00 h                                  
0   0     1     N/A                                                       
0   1     0     Enable Offset Frequency Register                          
                                    08 h                                  
0   1     1     Enable Center Frequency Register                          
                                     0 Ch                                 
1   0     0     Enable Timer Increment Register                           
                                    10 h                                  
1   0     1     Enable Initialize Phase Accumulator                       
                                    14 h                                  
                Register                                                  
1   1     0     Enable Initialize Timer Register                          
                                    18 h                                  
1   1     1     N/A                                                       
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     Microcontroller 22 next supplies the hexadecimal number 08 to the mode control and count register 44 (line 119 of the MAIN program of Appendix A). Hexadecimal 08, which is binary 0,0,0,0,1,0,0,0, is the DMA Mode Enable Offset Frequency Register as set forth in Table III. 
     The three control bits M2, M1 and M0 are supplied from mode control and count register 44 through a three input MCELL buffer 46 to the REG --  SEL[2..0] inputs of Numerical Controlled Oscillator DMA Controller circuit 48. 
     Microcontroller 22 also supplies the hexadecimal number 02 to the mode control and count register 44 (line 119 of the MAIN program of Appendix A). The hexadecimal number 02 has a binary value of 0,0,0,0,0,0,1,0 which in accordance with the following table is the BFSK (Binary Frequency shift key) mode of operation. 
     
                       TABLE IV                                                    
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F0           Function Load Value                                          
______________________________________                                    
0            Disabled 00 h                                                
1            BFSK     02 h                                                
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     At this time it should be noted that oscillator data and control circuit 38 is a Model EPM5128A EPLD (Erasable Programmable Logic Device) manufactured by Altera Corporation of San Jose, Calif. The EPM5128A EPLD uses an Altera Development Program the files set forth in Appendix C and the following table to provide the logic functions shown in FIGS. 2a-2c. 
     
                       TABLE V                                                     
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Logic Element                                                             
(FIGS. 2a-2c)  File (Appendix C)                                          
______________________________________                                    
mode control and count                                                    
               REG CONTROLLER                                             
register 44                                                               
MCELL buffers 46, 47                                                      
               MCELL3 BUFFER                                              
and 49                                                                    
DMA controller circuit 48                                                 
               NCO DMA CONTROLLER                                         
register controller                                                       
               NCO REGISTER CONTROLLER                                    
circuit 50                                                                
RAM address controller                                                    
               RAM ADDRESS CONTROLLER                                     
52                                                                        
RAM address comparator                                                    
               RAM ADDRESS COMPARATOR                                     
54                                                                        
slew controller circuit 56                                                
               SLEW CONTROLLER                                            
BFSK controller circuit 58                                                
               BFSK CONTROLLER                                            
MCELL buffers 60 and 61                                                   
               MCELL10 BUFFER                                             
PSK controller circuit 62                                                 
               PSK CONTROLLER                                             
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     Microcontroller 22 also supplies a pair of logic one manual load pulses to the MAN --  LOAD input of oscillator data and control circuit 38. The manual load pulse then passes through an OR gate 64 to the LOAD input of DMA controller circuit 48. The first manual load pulse from microcontroller 22 (lines 102 and 103 of the MAIN program of Appendix A) effects a transfer of the thirty two bits representing the lower frequency of 9.5 Mhz. The second manual load pulse from microprocessor 22 (lines 129 and 130 of the MAIN program of Appendix A) effects a transfer of the thirty two bits representing the offset frequency of 1.0 Mhz. 
     Numerical Controlled Oscillator DMA Controller circuit 48, in response to the first and second manual load pulses and the control bits M1, M2 and M3, generate address bits A2, A1 and A0 and chip select and write enable signals to load the least and most significant bits of the lower frequency into LSB and MSB lower frequency input registers within oscillator 36 as well as the least and most significant bits of the offset frequency into LSB and MSB offset frequency input registers within oscillator 36. 
     The following table illustrates the addressing requirements for loading the LSB and MSB center frequency input registers and the LSB and MSB offset frequency input registers within oscillator 36. 
     
                       TABLE VI                                                    
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A2,A1,A0    Function                                                      
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0       0     0     Load least significant bits of Center                 
                    Frequency Input                                       
0       0     1     Load most significant bits of Center                  
                    Frequency Input                                       
0       1     0     Load least significant bits of Offset                 
                    Frequency Input                                       
0       1     1     Load most significant bits of Offset                  
                    Frequency Input                                       
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     When at the logic zero state the chip select signal enables the data from RAMs 30 and 32 to be written into numerically controlled oscillator 36. The write enable signal is an active low. Data from RAMS 30 and 32 is clocked into the register within oscillator 36 selected by the address bits A2, A1 and A0 on the rising edge of the write enable signal when the chip select signal is a logic zero. 
     At this time it should be noted that Numerical Controlled Oscillator DMA Controller circuit 48 is a state machine having states SO through $7. The functions processed by DMA Controller circuit 48 during each state are set forth in the file NCO DMA CONTROLLER of Appendix C. 
     As is best illustrated by the timing waveforms of FIG. 3, during state S0 (FIG. 3N) the state machine of DMA Controller circuit 48 enters a power up mode. The RESET input (FIG. 3B) to oscillator data and control circuit 38 is initially active low, while the RAM --  OE line (FIG. 3H), the RAM-CS1 line (FIG. 3F) and the RAM --  CS2 line (FIG. 3G) are each in a tri-state mode since microcontroller 22 is controlling these lines. 
     When the RESET input of oscillator data and control circuit 38 (FIG. 3B) transitions to the logic one state then the RAM --  OE output (FIG. 3H), the RAM-CS1 output (FIG. 3F) and the RAM --  CS2 output (FIG. 3G) of DMA Controller circuit 48 each transition to the logic one state which results in oscillator data and control circuit 38 having control of read operations from RAMS 30 and 32. During State S0 the NCO --  CS output (FIG. 3I), the NCO --  WR output (FIG. 3J) the NCO --  LOAD --  REG output (FIG. 3K) and the FREQ --  INC of DMA Controller circuit 48 are each inactive. In addition during state S0, the address lines NCO --  A(0)-NCO --  A(2) of circuit 48 are each zero (FIG. 3M). The REG --  SEL (2..0) inputs (FIG. 3E) which receive bits D4, D3 and D2 of the mode control word is two through each state S0-S7. 
     When microcontroller 22 asserts the manual load signal causing the LOAD input of DMA Controller circuit 48 to transition to the logic one state (FIG. 3C), an internal RUN signal within DMA Controller circuit 48 transitions to the logic one state (FIG. 3D). The RUN signal of FIG. 3D enables the state machine within DMA Controller circuit 48. 
     An oscillator 37 supplies a 20 Mhz system clock signal (FIG. 3A) to the SYS --  CLK input of oscillator data and control circuit 38 After the RUN signal of FIG. 3D transitions to the logic one state, the first clock pulse 70 of the 20 Mhz system clock signal of FIG. 3A the state machine proceeds to state S1. The second clock pulse 72 causes the state machine to proceed to state S2. When the state machine enters state S2, the RAM --  OE output (FIG. 3H), the RAM-CS1 output (FIG. 3F), the RAM --  CS2 output (FIG. 3G), the NCO --  CS output (FIG. 3I) and the NCO --  WR output (FIG. 3J) are each asserted, that is each output transitions to the logic state. This, in turn, effects a read operation from RAMS 30 and 32 putting an eight bit data word from RAM 30 on the DATA --  A(7:0) lines and an eight bit data word from RAM 32 on the DATA(7:0) lines. 
     The next clock pulse 74 of the 20 Mhz system clock signal of FIG. 3A causes the state machine to transition to state S3. When the state machine of DMA controller circuit 48 transitions state S3 the numerically controlled oscillator write signal (NCO --  WR) of FIG. 3J will transition from a logic zero to a logic one. This transition of clock pulse 74 effects a write of the eight bit data word the DATA --  A(7:0) lines and the eight bit data word on the DATA(7:0) lines into numerically controlled oscillator 36. In a like manner, a logic zero to one transition of the clock pulse 80 (FIG. 3A) effects a write of second sixteen bit data word from RAMS 30 and 32 into numerically controlled oscillator 36. The first 32 bit data word written into numerically controlled oscillator 36 from RAMS 30 and 32 by the state machine of DMA controller 48 is the hexadecimal number 4C000000 which is the 9.5 Mhz lower frequency. 
     It should be noted that the waveforms of FIG. 3 illustrate the loading of the offset frequency into oscillator 36 since the numerical value of FIG. 3E is two. The timing waveforms of FIG. 3 will be identical for loading the lower frequency except that the numerical value of FIG. 3E is three. 
     When microcontroller 22 again supplies a logic one to the MAN --  LOAD input of oscillator data and control circuit 38 (line 129 of the MAIN program) the state machine of DMA Controller circuit 48 will effect a write of the 32 bit data word for the offset frequency into numerically controlled oscillator 36. 
     During state S4 the frequency increment pulse of FIG. 3L is provided by DMA Controller circuit 48 to the FREQ --  INC input of RAM address controller 52 which increments RAM address controller 52 thereby providing a new address to RAM 30 and 32 which allows the read of the second of the sixteen bit data words from RAMS 30 and 32 during state S5 and the subsequent write of the second of the sixteen bit data words into oscillator 36 at the leading edge of the clock pulse 80 of FIG. 3A. 
     At this time it should be noted that the load center frequency and load offset frequency portions of the MAIN program each include an ENA RAM subroutine which allows the oscillator data and control circuit 38 to be reset by supplying a logic zero to the RESET input of circuit 38. This logic zero, in turn, resets the state machine of Numerical Controlled Oscillator DMA Controller circuit 48 to state S0 (FIG. 3N). 
     Oscillator data and control circuit 38 also includes a register controller circuit 50 which supplies control signals ENOFREG and ENCFREG to numerically controlled oscillator 36. The ENOFREG signal is an active low signal. When the ENOFREG signal is active after being clocked into oscillator 36 by the 32 Mhz oscillator clock signal, the ENOFREG signal enables the clocking of data into the Offset Frequency Register within Oscillator 36. After the Offset Frequency Register is enabled a second clock pulse of the 32 Mhz oscillator clock signal is required to load the Offset Frequency Register within oscillator 36. 
     The ENCFREG signal is also an active low signal. When the ENCFREG signal is active after being clocked into oscillator 36 by the 32 Mhz oscillator clock signal, the ENCFREG signal enables the clocking of data into the Center Frequency Register within Oscillator 36. After the Center Frequency Register is enabled a second clock pulse of the 32 Mhz oscillator clock signal is required to load the Center Frequency Register within oscillator 36. 
     It should also be noted that prior to a manual load the MAIN program of Appendix A at lines 99 and 126 enters the DIS RAM subroutine which disables microcontroller 22 from RAMS 30 and 32 allowing oscillator data and control circuit 38 to effect data transfers from RAMS 30 and 32 to sixteen bit numerically controlled oscillator 36. 
     Oscillator data and control circuit 38 includes a binary frequency shift key (BFSK) controller circuit 58 which when enabled allows serial binary data stream from an external source, not shown, to first pass through the source A input of circuit 38 and then pass through BFSK controller circuit 58 of circuit 38 to the /INHOFR input of sixteen bit numerically controlled oscillator 36. When control bit D1 is a logic one, mode control and count register 44 supplies a logic to the MODE --  ENA input of BFSK controller circuit 58 enabling BFSK controller circuit 58. 
     The serial binary data stream passes through a control register within oscillator 36 to the control input of a multiplexer within oscillator 36. Depending upon the value of a bit the multiplexer will allow the 1 Mhz offset frequency to pass therethrough and be added to the lower frequency of 9.5 MHz by an adder within oscillator 38 or inhibit the 1 Mhz offset frequency from passing through the multiplexer within oscillator 38. When, for example, a bit within the serial binary data stream is a logic one, the 1 Mhz offset frequency is added to the 9.5 Mhz lower frequency resulting in a 16 bit 10.5 Mhz digitized sinewave at the SIN0-SIN15 outputs of oscillator 36. When, however, a bit within the serial binary data stream is a logic zero, the 1 Mhz offset frequency is inhibited from passing through the multiplexer within oscillator 36 which results in a 16 bit 9.5 Mhz digitized sinewave at the SIN0-SIN15 outputs of oscillator 36. The twelve most significant bits of the digitized sinewave signal are then supplied to the D0-D11 inputs of digital to analog converter 40. Digital to analog converter 40 converts the digitized signal to an analog sinewave signal having a frequency of 10.5 Mhz whenever a bit within the serial binary data stream is one and 9.5 Mhz whenever a bit within the serial binary data stream is zero. 
     At this time it should be noted that the digital to analog converters 40 and 44 used in the present invention are Model Q2520 D/A converters manufactured by Qualcomm Incorporated of San Diego, California. 
     From the foregoing, it may readily be seen that the present invention comprises a new, unique and exceedingly useful electronics circuit which may be used to frequency shift keying a continuous-running carrier, such as a sinewave. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. ##SPC1##