Abstract:
The present invention is a noise tolerant communication protocol device and method where a clock signal input, triggers an internal delay clock in an integrated circuit. Data is presented to an input pin and sampled prior to the next external clock pulse based on the internal delay clock. A data pulse value is distinguished by input signal voltage level and not by pulse length. Sampling of data bits is deferred until a signal level is most likely stable, thereby avoiding sampling during periods around edges of changing data values. Therefore, error detection and correction circuitry is not required. A time reference pulse, produced by a bus master, is measured by the protocol device, in determine a data transmission rate by the master. The timing of sampling of input signaling from the master is determined by the protocol, device from measurement of the time reference pulse magnitude.

Description:
RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 11/618,542, filed Dec. 29, 2006, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to an apparatus and method for communication protocols. More specifically, the present invention pertains to an apparatus and method for implementing a communication protocol transmitted over a single wire. 
       BACKGROUND ART 
       [0003]    Serial memory devices typically have a single input clock pin and a single input/output (I/O) pin for providing data. Although there are many product specific and proprietary protocols for accessing such devices, many industry standards are known and in the public domain. 
         [0004]    Communications of data and clock information frequently occurs via a single-wire form of transfer. Such communications are often used in memory chip transfers (e.g., between flash memory, EEPROMs, etc.) Some prior art schemes use a pulse width of the data to define the protocol. For example, the duration of a “1” data pulse is longer than a duration of a “0” data pulse.  FIG. 1A  shows an ideal output utilizing a pulse width modulation protocol. A first pulse  101  is indicative of a “0” (or logic low) transmission while a second-pulse  103  is indicative of a “1” (or logic high) transmission. 
         [0005]    A problem with this pulse width protocol is that noise can affect it in such a way that it becomes difficult to determine the duration of the data pulse. Consequently, errors occur in reading the data pulses.  FIG. 1B  shows an example of a typical prior art transmission signal with noise. A first pulse  105  is indicative of a “0” transmission. However, a second pulse train  107  and a third pulse train  109  cannot be clearly discerned due to excessive noise. Indeed, the second and third pulse trains  107  and  109  each contain a plurality of data pulses, although an exact number of pulses is unknown. 
         [0006]    Error detection and correction circuits are generally used with protocols of this type to alleviate the inaccuracies in reading the data. However, these error detection/correction circuits take up valuable real estate on an integrated circuit chip. Therefore, it is not desirable to use pulse width modulation protocols and rely on error correction techniques to accurately transmit clock and data over a single wire. 
         [0007]    What is needed is a high speed read access in a serial, single wire transmission which can be achieved without excessive circuitry and/or cost. It is a further desire to provide such capability without excessive power requirements. 
       SUMMARY 
       [0008]    The present invention solves the aforementioned problems by providing noise tolerant communication protocol in which a delay clock is created internally in an integrated circuit when all input signal transitions from logic high to logic low in one embodiment, this could be the falling edge of an external clock signal. During a predefined delay time, data can be presented to an input pin and can be sampled prior to the next external clock pulse. The protocol does not rely on the length of the data pulse to determine a value of the data (i.e., whether data is a “1” or “0”). Rather, “0&#39;s” and “1&#39;s” are distinguished by a voltage level of the signal. Sampling of data bits is deferred until that signal level is likely to be stable thereby avoiding sampling during periods around rising or falling edges associated with changing data values. Therefore, noise should not affect reading of the data and error detection and correction circuitry is not required. 
         [0009]    In one embodiment of the present invention, one hit of data is sampled per external clock cycle. This embodiment encompasses bath a device and a method for its use. The electronic device samples an external clock pulse and a data bit from a single wire communication system through a data input terminal. A pulse generator produces a pulse whenever an external clock pulse is input. A first delay element coupled to the poise generator produces a delayed pulse. Together, the pulse generator and the first delay element form a portion of an internal clock used for timing various functions within the device. Input data bits are latched in and output data are valid only during a stable portion of each data bit. The latch, for example, a D-type flip-flop, is enabled by the internal clock. A second delay element produces a delay between the input data input terminal and the latch. The second delay ensures that the external clock pulse is prevented from reaching the latch while the latch is enabled. 
         [0010]    In another embodiment of the present invention, a plurality of data bits is sampled per external clock cycle. This embodiment also encompasses both a device and a method for its use. The electronic device samples an external clock pulse and data bits from a single wire communication system, through a data input terminal. A pulse generator produces a pulse whenever an external clock pulse is input. A first delay element is coupled to the pulse generator for producing a delayed pulse. Together, the first pulse generator and the first delay element form a portion of an internal clock. A first latch, for example, an SR latch, is used to enable the first pulse generator during a period of time when the external clock pulse is present on the single wire input. The external clock then serves as a trigger for the first pulse generator. A second latch, for example, a D-type flip-flop, is enabled by the internal clock for latching each of the data bits and producing an output. The second latch is enabled only during a period of time when the data bits are stable. A counter, for example, a count-by-n counter, is used for determining when all data hits within a given cycle have been latched. The counter then resets the device in preparation for a subsequent serial communication cycle. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1A  is an ideal pulse train of the prior art employing pulse width modulation to distinguish logic high and logic low data states. 
           [0012]      FIG. 1B  is a simulated actual pulse train with noise employing pulse width modulation of the prior art to distinguish logic high and logic low data states. 
           [0013]      FIG. 2  is an exemplary schematic circuit diagram of a single-bit implementation of the present invention to provide a communication protocol from over a single wire. 
           [0014]      FIG. 3  is a timing diagram of the circuit of  FIG. 2 . 
           [0015]      FIG. 4  is another exemplary schematic circuit diagram of a single-bit implementation of the present invention to provide a communication protocol from over a single wire. 
           [0016]      FIG. 5  is a timing diagram of the circuit of  FIG. 4 . 
           [0017]      FIG. 6  is a schematic circuit diagram of an exemplary multi-bit implementation of the present invention to provide a communication protocol from over a single wire. 
           [0018]      FIG. 7  is a timing diagram of the circuit of  FIG. 6 . 
           [0019]      FIG. 8  is a flowchart of a method of operation of the schematic circuit of  FIG. 2 . 
           [0020]      FIG. 9  is a flowchart of a method of operation of the schematic circuit of  FIG. 4 . 
           [0021]      FIG. 10  is a flowchart of a method of operation of the schematic circuit of  FIG. 4 . 
           [0022]      FIG. 11  is a flowchart of a method of operation of the schematic circuit of  FIG. 4 . 
           [0023]      FIG. 12  is an exemplary timing diagram of a single wire protocol. 
           [0024]      FIG. 13  is an exemplary schematic diagram of a time reference circuit. 
           [0025]      FIG. 14  is a timing diagram of the circuit of  FIG. 13 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    With reference to  FIG. 2 , an exemplary embodiment of a single-bit noise resistant circuit  200  is shown. The single-bit noise reduction circuit  200  includes a first delay element  201 , a D-type flip-flop  203 , a single-pulse generator  205 , a second delay element  207 , an SR-type latch  209 , a third delay element  211 , and a fourth delay element  213 . 
         [0027]    As shown in this exemplary embodiment, a combination external clock and data pulse train enters the single-bit noise resistant circuit  200  at a single wire input and is concurrently fed into an input of the single-pulse generator  205  and the first delay element  201 . Assuming the SR latch  209  is in a “set” position, a failing edge of an incoming external clock pulse produces a pulse at an output of the single-pulse generator  205 . The pulse produced at the output of the pulse generator  205  starts an internal clock and follows two paths. First, the pulse propagates through the third delay element  211 , thereby forcing the SR latch  209  into a reset position. Secondly, the pulse propagates through the second delay element  207 , and is again split, reducing an enable pulse for the D-type flip-flop  203 , and concurrently propagating through the fourth delay element  213 . Once the pulse has propagated through the fourth delay element  213 , the SR latch  209  is placed back in a “set” state. However, the third delay element  211  is chosen to have a propagation delay which is less than the total propagation delay of the second and the fourth delay elements  207 ,  213  combined. This difference in delay creates a window in time during which only data is gathered from the incoming clock and data pulse train. The second delay element  207  is chosen to enable the flip-flop  203  only when a data pulse is present, thereby excluding external clock pulses from appearing at an output of the flip-flop  203 . The clock pulse is not latched as part of an output pulse from the single-bit noise resistant circuit as described infra with regard to a single-bit protocol timing diagram. Letters “A”-“E” serve as references for a timing diagram of  FIG. 3 . 
         [0028]      FIG. 3  shows an exemplary single-bit protocol timing diagram  300  for the single-bit circuit  200  of  FIG. 2 . The timing diagram  300  comprises the constituent timing diagram of each significant input and output of the single-bit noise resistant system  200  of  FIG. 2 . (Note that each line of the timing diagram “A”-“E” references a particular point in the circuit  200 ). A constituent timing diagram changes state only when an event represented by another constituent event occurs. The timing diagram includes an initial clock pulse  301 , an initial data pulse  303  (or lack of a pulse for a “0” data value), a single-pulse generator enable signal  305 , a  31 ) single-pulse generator disable period  307 , a single-pulse generator re-enable signal  309 , an SR latch set pulse  311  (prior to propagation through the delay element  213 ). a delayed initial clock pulse  313 , a delayed initial data pulse  315 , a non-inverted latched output  317 , and a start of a subsequent clock cycle  319 . The initial data pulse  303  is shown at a high (i.e., “1”) logic level for aid in understanding the timing diagram  300 . However, one skilled in the art will recognize that a low logic data level will function appropriately. 
         [0029]    On operation of the single-bit circuit  200 , the clock/data pulse train concurrently passes to the first delay element  201  and the single-pulse generator  205 . After propagation, an output from the first delay element  201  produces a delayed initial clock pulse  313  and the delayed initial data pulse  315 . 
         [0030]    A second portion of the clock/data pulse train continues as follows. Assuming the SR latch  209  is in the set position, the single-pulse generator  205  is enabled by the enable signal  305 . A falling edge of the initial clock pulse  301  then forces the single-pulse generator  205  to produce an output pulse as shown at “B.” After the delay incurred propagating through the third delay element  211 , the pulse shown at “C” sends a reset to the SR latch  209 . While the SR latch is in a reset position, an output from the SR latch  209  is forced low, thereby placing the single-pulse generator  205  into a disabled period. 
         [0031]    The output pulse from the generator  205  also propagates through the second delay  207 , enabling the D-type flip-flop  203 . However, notice that the delayed clock pulse  313  occurs prior to the D-type flip-flop being enabled (at “E”). Therefore, the clock pulse is stripped from the clock/train pulse input to the single-bit circuit  200  and anon-inverted data pulse appears as the latched output  317  (at reference “H”). After an additional delay, the pulse at “E” propagates, causing the SR set pulse  311  (at reference “F”), thereby producing the pulse generator re-enable signal  309  for pulse generator  205  to be enabled for the start of a subsequent clock cycle  319 . Further, the D-type flip-flop  203  is only enabled to latch to the data pulse  303  after the data pulse  303  is in a stable region (see the delayed initial data pulse  315  at “G”), thereby ensuring reliability of data latched at the output of the D-type flip-flop  203 . The delay path through the fourth delay element  213  is designed to be long enough to ensure the data pulse train is not interpreted as a clock to the D-type flip-flop  203 . Blocking the input data from being interpreted as an input clock is accomplished by holding “D” low  307  which disallows the data pulse from generating a clock pulse from the pulse generator  205 . 
         [0032]    With reference to  FIG. 4 , another exemplary embodiment of a single-bit noise resistant circuit  400  incorporates a single wire to output data. The single-bit noise reduction circuit  400  includes a first delay element  401 , a first D-type flip-flop  403 , a first single-pulse generator  405 , a second delay element  407 , an SR-type latch  409 , a third delay element  411 , a second single-pulse generator  412 , a fourth delay element  413 , a fifth delay element  415 , and an output circuit  421 . 
         [0033]    The output circuit  421  includes a sixth delay element  423 , an enable select block  425 , an inverting delay element  427 , a second D-type flip-flop  429 , an inverter  431 , and a pull-down transistor  433 . 
         [0034]    As shown in this exemplary embodiment, a combination clock and data pulse train is output to the bus. The single-bit noise resistant circuit  400  has a single wire input which is concurrently coupled to the output circuit  421 , an input of the single-pulse generator  405 , and the first delay element  401 . Assuming the SR latch  409  is in a “set” position, a falling edge of all incoming external clock pulse produces a pulse at an output of the single-pulse generator  405 . The pulse produced at the output of the pulse generator  405  starts an internal clock. The pulse propagates through the second delay element  407 , and follows two paths, First, the pulse forces the SR latch  409  into a reset position. Secondly, the pulse propagates through the fifth delay element  415 , and is again split, producing an enable pulse for the D-type flip-flop  403 , and concurrently propagating through the third delay element  411 . Once the pulse has propagated through the third delay element  411 , a falling edge of the pulse triggers a second single-pulse generator  412  to produce a pulse. The pulse from the second single-pulse generator  412  propagates through the fourth delay element  413 , thereafter forcing the SR latch  409  back to a “set” position. 
         [0035]    Relative delay times for each delay element are chosen to create a window in time during which only data are gathered from the incoming clock and data pulse train. Relative delays shown are exemplary only and may be modified by methods known to a skilled artisan depending upon factors such as delay between external clock pulses, delay between external clock and data pulses, relative data pulse durations, and so on. 
         [0036]    For general guidance, the first delay element  401  is utilized for noise reduction purposes, The second delay element  407  ensures an adequate pulse width at point “C.” Otherwise, the pulse at “C” could be very narrow and be filtered at a subsequent stage. The fifth delay element  415  prevents the first flip-flop  403  from becoming enabled prior to latching a stable data portion of the data pulse and additionally preventing a clock pulse from being latched during data input situations. The fifth delay element  415  works in conjunction with the second delay element  407  and is chosen to enable the first flip-flop  403  only when a data pulse is present, thereby excluding external data In pulses or data out pulses from entering the clock pin of the first flip-flop  403 . The third delay element  411  works in conjunction with the fourth delay element  413  to allow sufficient delay time for the data pulse to fully propagate so as to prevent the SR-latch from being in a “set” position (thereby ensuring that the single-pulse generator  405  is not enabled). One skilled in the art will recognize that the third and fourth delay elements  411 ,  413  may be combined into a single delay element depending on external clock/data pulse parameters discussed supra. 
         [0037]    When various delays are properly selected as described, the clock pulse is not latched as part of an output pulse from the single-bit noise resistant circuit, as described infra, with regard to a single-hit protocol timing diagram. Letters “A”-“H” and “K”-“N” serve as references for a timing diagram of  FIG. 5 . 
         [0038]    The output circuit  421  is configured to output data, at “J,” from an internal. memory, and, once latched by the second D-type flip-flop  429 , to enter a main portion of the single-bit noise resistant circuit, described supra. The second inverter  431  and the second pull-down transistor  433  serve to pull the output low for outputting a logic zero. A skilled artisan will recognize that there may be ways to further simplify the logic of  FIG. 4  or alternate methods to accomplish the same suggested protocol and still he within the scope of the present invention. 
         [0039]      FIG. 5  shows an exemplary single-bit protocol timing diagram  500  for the single-bit circuit  400  of  FIG. 4 . The timing diagram  500  comprises the constituent timing diagram of each significant input and output of the single-bit noise resistant system  400  of  FIG. 4 . (Note that each line of the timing diagram “A”-“H” and “K”-“N” references a particular point in the circuit  400 ). A constituent timing diagram changes state only when an event represented by another constituent event occurs. The timing diagram includes an initial clock pulse  501 , an output pulse  503  (or lack of a pulse for a “0” data, value), a single-pulse generator enable signal  505 , a single-pulse generator disable period  507 , a single-pulse generator re-enable signal  509 , an SR latch set pulse  511  (prior to propagation through the third and fourth delay elements  411 ,  413 ), a delayed initial clock pulse  513 , a delayed initial data pulse  515 , a non-inverted latched output  517 , an SR latch set pulse  519  (after propagation through the third and fourth delay elements  411 ,  413 ), and a start of a subsequent clock cycle  521 . The initial data pulse  503  is shown at a high (i.e., “1”) logic level for aid in understanding the timing diagram  500 . However, one skilled in the art will recognize that a low logic data level will function appropriately. Additionally, an output of the optional second D-type flip-flop  429  at “M” depends on a state of a clock pulse at “K,” an enable signal at “L,” and a state of incoming secondary data from on-chip memory elements at “J.” 
         [0040]    On operation of the single-hit circuit  400 , the clock/data pulse train concurrently passes to the first delay element  401  and the single-pulse generator  405 . After propagation, an output from the first delay element  401  produces a delayed initial clock pulse  513  and the delayed initial data pulse  515 . 
         [0041]    A second portion of the clock/data pulse train continues as follows. Assuming the SR latch  409  is in the set position, the single-pulse generator  405  is enabled by the enable signal  505 . A falling edge of the initial clock pulse  501  then forces the single-pulse generator  405  to produce an output pulse as shown at “B.” After the delay incurred propagating through the second delay element  407 , the pulse shown at “C” sends a reset to the SR latch  409 . While the SR latch is in a reset  5  position, an output from the SR latch  409  is forced low, thereby placing the single-pulse generator  405  into a disabled position. 
         [0042]    The output pulse from the generator  405  also propagates through the second and fifth delay elements  407 ,  415 , thereby enabling the first D-type flip-flop  403 . However, notice that the delayed clock pulse  513  occurs prior to the first D-type flip-flop being enabled (at “E”). Therefore, the clock pulse is stripped from the clock-data train pulse input to the single-bit circuit  400  and a non-inverted data pulse appears as the latched output  517  (at reference “H”), After an additional delay, the pulse at “E” propagates, causing the SR set pulse  519  (at reference “N”), thereby producing the pulse generator re-enable signal  509  for pulse generator  405  to be enabled for the start of a subsequent clock cycle  521 . Further, the first D-type flip-flop  403  is only enabled to latch to the data pulse  503  after the data pulse  503  is in a stable region (see the delayed initial data pulse  515  at “G”), thereby ensuring reliability of data latched at the output of the D-type flip-flop  403 . 
         [0043]      FIG. 6  shows an exemplary embodiment of a multi-bit noise resistant circuit  600 . The multi-bit noise resistant circuit  600  includes an OR gate  601 , a D-type flip-flop  603 , a single-pulse generator  605 , a first delay element  607 , an SR-type latch  609 , a second delay element  611 , a third delay element  613 , a count-by-n element  615 , and a monostable multivibrator (“one-shot”)  617 . 
         [0044]    As shown in this exemplary embodiment, a combination external clock and data pulse train enters the multi-bit noise resistant circuit  600  at a single wire input and is concurrently fed into an input of the single-pulse generator  605  and the D-type flip-flop  603 . Assuming the SR latch  609  is in a “set” position a falling edge of an incoming external clock pulse produces a pulse at an output of the single-pulse generator  605 . The pulse produced at the output of the pulse generator  605  starts an internal clock. The output of the pulse generator  605  is coupled to the second delay element  611 . A pulse from an output of the second delay element  611  resets the SR latch  609 . Concurrently the pulse is also an input to the OR gate  601 . While at least one input of the OR gate is high, the one-shot  617  produces a pulse which is fed into the first delay element  607 . An output of the first delay element  607  enables the D-type flip-flop  603 . Concurrent with the flip-flop enablement an output of the first delay element  607  is also fed back to the OR gate  601  and to an input of the count-by-n element  615 . The count-by-n element  615  may be, for example, an n-bit binary counter comprised of sequential logic. Once the count-by-n element  615  has achieved a desired count level, a pulse is transmitted into the third delay element  613 . A delayed pulse from the third delay element  613  then places the SR latch  609  in a set position. When in a set position, an output of the SR latch  609  then enables the single-pulse generator  605  in preparation for a subsequent clock/data pulse train. An operation of the multi-bit noise resistant circuit  600  will be described in detail, infra. Letters “A”-“H” and “J” serve as references for a timing diagram of  FIG. 7 . 
         [0045]      FIG. 7  shows an exemplary single-bit protocol timing diagram  700  for the multi-bit noise resistant circuit  600  of  FIG. 6 . The timing diagram  700  comprises the constituent timing diagram of each significant input and output of the multi-bit circuit  600  of  FIG. 6 . A constituent timing diagram changes state only when an event represented by another constituent event occurs. The timing diagram includes an initial clock pulse  701 , a plurality of initial data pulses  703 , a single-pulse generator enable signal  705 , a single-pulse generator disable period  707 , a single-pulse generator re-enable signal  709 , an OR gate logic output  711 , a one-shot output pulse  713 , a first D-type flip-flop enable signal  715 , a final D-type flip-flop enable signal  717 , a count-by-n output pulse  719 , an SR set pulse  721 , and a start of a subsequent clock/data pulse train  723 . The initial plurality of data pulses  703  are shown at a high logic level (i.e., “1”) to aid in understanding the timing diagram  700 . However, one skilled in the art will recognize that a low logic data level will function appropriately. 
         [0046]    Unlike the single-hit noise resistant circuit  200  ( FIG. 2 ) which passes through the first delay element  201  prior to the flip-flop  203 , the clock data pulse train in the multi-bit circuit  600  passes directly to the D-type flip-flop  603 . However, since the flip-flop  603  is not enabled, the initial clock pulse  701  is not latched to an output of the flip-flop  603 . The SR latch  609  is in a set position at “D” and is therefore sending a single-pulse generator enable signal  705  to the single-pulse generator  605 , thereby allowing an output pulse at “B” when triggered by the initial clock pulse  701 . The output from the single-pulse generator  605  is also transmitted to the second delay element  611  causing a delayed pulse at “C.” The delayed pulse at “C” forces a reset on the SR latch  609 , While the SR latch  609  is in the reset position, an output from the SR latch  609  is forced low, placing the single-pulse generator  605  into a disabled period  707 . Concurrent with the delayed output pulse resetting the latch  609 , the delayed pulse is also transmitted through the OR gate  601  producing an OR gate logic output  711  at “E.” The OR gate logic output  711  triggers the one-shot  617  producing the one-shot output  713  at “F.” The one-shot output  713  is transmitted through the first delay element  607  producing the enable signal  715  for the D-type flip-flop  603 , thereby latching a first of the plurality of initial data pulses  703  during a stable period of the first data pulse. Concurrently, the flip-flop enable signal  715  is also transmitted to the one-shot  617  through the OR gate  601 . This transmitted pulse repeats the data read/latch cycle just described and depicted at “E,” “F,” and “G.” Once the count-by-n element  615  reads the final data signal  717 , the count-by-n element  615  produces the count-by-n pulse  719 . The count-by-n pulse  719  is transmitted through the third delay element  613  producing the SR latch set pulse  721  at “J.” In turn, the SR set pulse  721  sends the re-enable signal  709  to the single-pulse generator  605 , thus resetting the multi-bit circuit  700  for the start of the subsequent clock/data pulse train  723 . 
         [0047]    With reference to  FIG. 8 , a flowchart  800  of a method of operation of the single-bit noise resistant circuit  200  of  FIG. 2  is presented. Initially, au external clock/data pulse train is presented to the single-bit circuit  200 . From there, the pulse is split into two paths. On the left, an internal clock pulse is started. At step  803 , if the single-pulse generator  805  is enabled, a single pulse is generated using the external clock pulse as a trigger  605 . The pulse is split a second time into two paths. 
         [0048]    The left branch of the second split delays the single pulse generated in step  805  for a time, t 1 , where t 1  is less than a summation of delay times t 2  and t 3 , discussed below. In general, all delay times are chosen based upon a specification of external clock pulse frequencies, pulse widths, and time between clock and data pulses. All required delays are readily determined by a skilled artisan and will not be elaborated upon herein. After the delay step  807 , a reset pulse  809  is sent to the SR latch  209 . 
         [0049]    The left branch of the second split starts with a second delay for a time t 2    811 . The pulse is split a third time into two additional branches. The left branch of the third split begins with a third delay for time t 3    813 . After the third delay step  813 , a set pulse is sent  815  to the SR latch  209 . A determination is made whether the latch  209  is set  817 . If the latch  809  is set, an enable pulse is sent  819  to the single-pulse generator  205 . Once the single-pulse generator  205  is enabled, the single-bit circuit is ready for a subsequent external clock and data pulse. 
         [0050]    After the initial split from step  801 , the right branch of the flowchart proceeds as follows. The clock/data pulse train is delayed for a fourth delay time t 4    823  prior to being transmitted to the flip-flop  203 . If the flip-flop  203  is enabled  827 , the data pulse is latched  829  and output  631 . Note that the flip-flop enable pulse occurs after step  811  when the enable pulse is sent to the flip-flop  203  in step  821 . The delays are calculated such that 1) the flip-flop  203  is not enabled during an external clock pulse, and 2) the data pulse is latched only during a data stable portion of the data pulse (see  FIG. 3  at “G”). 
         [0051]    With reference to  FIG. 9 , a flowchart  900  of a method of operation of the single-hit noise resistant circuit  400  of  FIG. 4  is presented. Notice that this flowchart is similar to flowchart  800  of  FIG. 8 . The primary significant differences between flowcharts  800  and  900  occur with reference to steps  901 ,  903 , and  905 . Step  901  accepts an optional input to the single-bit noise resistant circuit  400  from a secondary external clock-pulse data train. At step  903 , a single pulse is produced by the single pulse generator  405 . The generated pulse is then delayed in step  905  for time t=t 1  before taking bifurcated routes. Thus, the method of operation presented in flowchart  900  is in contrast to the route of the generated pulse immediately being bifurcated in step  805 . 
         [0052]      FIG. 10  shows a flowchart  1000  of a method of operation of the multi-hit noise resistant circuit  600  of  FIG. 6 . Initially, an external clock/dam pulse train is presented to the multi-bit circuit  600 . Similar to  FIG. 8 , the pulse is split into two paths. On the left branch, the clock/data pulse train is transmitted  1041  to the flip-flop  603 . On the right, an internal clock pulse is started. At step  1003 , if the single-pulse generator  605  is enabled, a single pulse is generated using the external clock pulse as a trigger  1005 . The pulse is then delayed for a time, t 1 ,  1007 . The pulse is then split a second time into two additional paths. On the right, a reset pulse is sent  1039  to the SR latch  609 , thereby preventing any additional pulses being generated by the single-pulse generator  605  until a subsequent external clock/data pulse train is received. Data pulses are unable to trigger a single pulse since the single-pulse generator  605  is not enabled while the SR latch  609  is in a reset condition. 
         [0053]    The left branch of the second split transmits the delayed pulse  1009  to the OR gate  601 . If a determination is made  1011  that at least one OR gate input is at logic high, the pulse is transmitted  1013  to the one-shot  617 , thereby generating a new pulse. The new pulse is delayed  1015  for time t 2 . After the time delay t 2    1015 , the pulse is split three ways. 
         [0054]    Starting with the far left branch, the delayed one-shot pulse is used to enable the flip-flop  603 . Once a determination is made  1043  that the flip-flop is enabled, the data pulse transmitted from step  1041  is latched  1019  and the data pulse is output  1021 . As with the flowchart  800 , the various delay times are established such that a clock pulse does not arrive at an output flip-flop while the flip-flop is enabled. Other timing elements are determined in a way well known to one skilled in the art. 
         [0055]    The center branch of the three-way split after step  1015  starts by transmitting a pulse to the count-by-n element  615  in step  1023 . An internal counter on the count-by-n element  615  is incremented  1025 . A determination  1027  is made whether the internal counter equals n. For example, if a clock/data pulse is designed to have 8 data pulses (i.e., n=8) between external clock pulses, than the count-by-n element  615  is chosen to be an eight bit counter. If the internal counter equals n (i.e., all n data hits have been received) the transmitted pulse is delayed for time t 3 . The delayed pulse  1033  is then transmitted to “set” the SR latch  609 , thereby preparing the multi-bit circuit  600  to receive a subsequent external clock/data pulse train. 
         [0056]    Concurrent with the pulse being transmitted to the count-by-n element  615  from step  1015 , the far right branch of the three-way split transmits the pulse  1029  to the OR gate  601 . This forces at least one input of the OR gate to logic high, so the cycle is repeated at step  1011  until the count-by-n element  615  equals n as described supra. Compare to  FIG. 3  at “E”-“H.” 
         [0057]    Similar to the method of operation  800  for the single-bit circuit  200 , the delays for the multi-hit method  1000  are calculated such that 1) the flip-flop  603  is not enabled during an external clock pulse, and 2) the data pulse is latched only during a data stable portion of the data pulse (see  FIG. 7  at “A”). 
         [0058]    With reference to  FIG. 11 , serial data output is produced with a single wire device from a data stream having one or more clock pulses in series with one or more input data bits in a serial data output method  1100 . The one or more input data bits are discerned  1110  from the one or more clock pulses in the data stream. The one or more input data bits are latched  1120  during a stable period of the data stream. Serial output data are produced  1130 , devoid of the one or more clock pulses, from either data from an internal memory or from the one or more input data bits. If a determination  1140  is made that the output is to be comprised of input data, then the output is appended  1160  with data from an internal memory. Otherwise, the output is produced from internal memory and appended  1150  with input data bits. 
         [0059]    With reference to  FIG. 12 , an input signal “I” on a single wire bus, ramps up during a power up time t 1  in an exemplary single wire protocol waveform diagram  1200 . A ramp up characteristic of the input signal “I” during the power up time t 1  is determined by a pullup resistor on the single wire bus. The pullup resistor may be external to a plurality of integrated circuits communicating on the bus and supplies a high logic level that driving devices within the integrated circuits may pull down against to produce electrical signaling. 
         [0060]    A second time frame of the input signal is a timeout period t 2 . The timeout period t 2  is provided so that once the high logic level is attained during the power up time t 1 , an amount of time is allowed to elapse within each integrated circuit on the bus before any communication is initiated. All transmit and receive circuitry within roaster and receiver integrated circuits is held in a quiescent state during the timeout period t 2  and no communication is undertaken. The timeout period t 2  ensures that no false starts of transmission occur during the power up phase of the bus due to noise or other incidental transitions that may occur during and immediately following the power up time t 1 . 
         [0061]    After the timeout period h elapses, a bus master, which may be for example, a microcontroller, produces a time reference pulse t r  on the single wire bus. The time reference pulse t r  produced by a bus master is an indication of the length of time making up one timeframe containing one quantity of data signaling. The duration of the time reference pulse t r  determines the frequency at which the bus master communicates data to receivers on the single wire bus. In order for a receiver to properly acquire data transmitted by the bus master, the receiver must sample the time reference pulse t r , determine its duration, and set up internal circuitry with timing that enables acquisition of data at the rate determined by the time reference pulse t r . 
         [0062]    In order for a receiver on the single wire bus to determine the duration of the time reference pulse t r , circuitry within the receiver must be able to effectively measure the duration of the pulse and calculate and appropriate response for setting up the timing of internal circuitry to be able to communicate at the rate determined by the time reference pulse. A calculation time t calc  is defined as a period of time following the time reference pulse t r  that a receiver is allowed for assessing the duration of the time reference pulse t r  based on certain calculations by internal circuitry to the receiver. 
         [0063]    Once the calculation time t calc  has transpired and circuitry internal to the receiver has determined a duration of the time reference pulse, essential characteristics of timing required in the receiver for sampling data from the bus master may be determined. Two quantities required for sampling data transmitted from the bus master are a sample delay time f 1  (t r ) and a sample time f 2  (t r ). Both the sample delay time f 1  (t r ) and the sample time f 2  (t r ) are a function of the magnitude of the time reference pulse t r . The sample delay time f 1  (t r ) is the amount of time following the transition of a clock signal on the single wire bus that circuitry within the receiver must wait before sampling for a transition of the input signal “I” corresponding to a data signal on the single wire bus. The sample delay time f 1  (t r ) is also an applicable wait time for the same circuitry within the receiver to wait after the final signal transition of a previous data timeframe before sampling for a subsequent data signal where a plurality of successive data bits are transmitted within a protocol. 
         [0064]    A further essential timing characteristic of the circuitry within the receiver is the sample time f 2  (t r ). This is the amount of time following the sample delay time f 1  (t r ) that transitions of a data signal may be sampled. The duration of the sample time f 2  (t r ) is in effect a sampling window and the sample delay time f 1  (t r ) is the timing characteristic that positions the sampling window within one single wire protocol time frame. Successive application of the sample delay time f 1  (t r ) and the sample time f 2  (t r ) after each trailing edge of a clock or prior data signal, provides proper timing for circuitry within the receiver to correctly sample data. 
         [0065]    With reference to  FIG. 13 , a single wire input signal “I” is applied at a single wire input  1305  of an exemplary schematic diagram of a time reference device  1300 . A sequence of, for example, five delay stages are connected in series. A delay stage may be composed of for example, two inverters connected in series with a capacitor. Alternatively, a number of inverter pairs and a value of the capacitor may be selected to add up to a desired delay of each stage. Additionally, delays of the delay stages may be chosen to be not equal to one another. For example a magnitude of delay for each stage may form a progression so that an increasing or decreasing value of delay between successive stages allows for an expansion in the scope of lime captured at a measurement time, or in the case of decreasing values, forms a finer grain resolution for determining a trailing edge of a reference pulse which may be applied at the single wire input  1305 . 
         [0066]    An input of a first delay stage  1310  connects to the single wire input  1305 . The series connections are made by an output of a previous delay stage connecting to an input of a successive delay stage. A first delay stage output signal “A” is produced at an output of the first delay stage  1310  where a connection is made to an input of a second delay stage  1320 . A second delay stage output signal “B” is produced at an output of the second delay stage  1320  where a connection is made to an input of a third delay stage  1330 . A third delay stage output signal “C” is produced at an output of the third delay stage  1330  where a connection is made to an input of a fourth delay stage  1340 . A fourth delay stage output signal “D” is produced at an output of the fourth delay stage  1340  where a connection is made to an input of a fifth delay stage  1350 . A fifth delay stage output signal “E” is produced at an output of the fifth delay stage  1350 . 
         [0067]    The first delay stage output signal “A” is provided to a data input of a first latch  1315  from the output of the first delay stage  1310 . A second delay stage output signal “B” is provided to a data input of the second latch  1325  from the output of the second delay stage  1320 . The third delay stage output signal “C” is provided to a data input of the third latch  1335  from the output of the third delay stage  1330 . The fourth delay stage output signal “D” is provided to a data input of the fourth latch  1345  from the Output of the fourth delay stage  1340 . The fifth delay stage output signal “E” is provided to a data input of a fifth latch  1355  from the output of the fifth delay stage  1350 . 
         [0068]    A first latch output signal “Q 0 ” is produced at an output of the first latch  1315 . A second latch output signal “Q 1 ” is produced at an output of the second latch  1325 . A third latch output signal “Q 2 ” is produced at an output of the third latch  1335 . A fourth latch output signal “Q 3 ” is produced at an output of the fourth latch  1345 . A fifth latch output signal “Q 4 ” is produced at an output of the fifth latch  1355 . 
         [0069]    A logic inversion device is connected to the single wire input  1305 . A logic inversion device output signal “I” is produced at an output of the logic inversion device  1365  and is provided to a clock input of each of the first latch device  1315 , the second latch device  1325 , the third latch device  1335 , the fourth latch device  1345 , and the fifth latch device  1355 . 
         [0070]    With reference to  FIG. 14 , the power up time t 1  ( FIG. 12 ) precedes the timeout period t 2  on a single wire input signal “I” in an exemplary time reference timing diagram  1400 . The high logic level produced on the single wire input signal by the pullup device on the single wire bus, propagates through the first delay stage  1310  and produces a high logic level on the first delay stage output signal “A” during the timeout period t 2 . Continued propagation of the high logic level through the remainder of the serially connected delay stages  1320 ,  1330 ,  1340 ,  1350  produces a succession of high logic levels on the remainder of the delay stage output signals “B”, “C”, “D”, “E”. 
         [0071]    The time reference pulse t r  ( FIG. 12 ) produced by the bus master, is provided to the single wire bus after the timeout period t 2 . In a similar fashion to the propagation of the high logic level during the timeout period t 2 , the time reference pulse t r  propagates through the delay stages  1310 ,  1320 ,  1330 ,  1340 ,  1350 . In a cascading fashion, the propagation of the time reference pulse t, produces a similar pulse occurring at an offset delay due to the delay within each of the serially connected delay stages  1320 ,  1330 ,  1340 ,  1350 . Therefore, a sequence of derivatives of the time reference pulse t r    1410 ,  1420 ,  1430 ,  1440 ,  1450  are produced in sequence on the delay stage output signals “A”, “B”, “C”, “D”, “E”. 
         [0072]    Propagation of the time reference pulse t, through the logic inversion device  1365  produces a derivation of the time reference pulse t r  as the logic inversion device output signal “I”. The derivation of the time reference pulse t r  may be for example, an inversion of the time reference pulse t r  produced at an output of the logic inversion device  1365 . As an inverted derivative of the time reference pulse t r , the trailing edge of the inverted time reference pulse is configured to produce a clock time signal t c . Formation of the derivative of the time reference pulse t r  is a configuration of a signal with an appropriate species of edge occurring at an appropriate time to operate as a clock signal for the series of latches  1315 ,  1325 ,  1335 ,  1345 ,  1355  ( FIG. 13 ). The clock time signal t c  is provided to the clock input of each of the series of latches  1315 ,  1325 ,  1335 ,  1345 ,  1355 . The clock time signal t c  causes the series of latches  1315 ,  1325 ,  1335 ,  1345 ,  1355  to activate and latch a signal level at each respective latch input. 
         [0073]    Propagation through the series connection of delay stages positions the time reference pulse t r  topologically and in time along the sequence of delay stage output signals “A”, “B”, “C”, “D”, “E”. The time reference pulse t r , at any given dine, is at a different stage of progression with respect to the input of each of the series of latches  1315 ,  1325 ,  1335 ,  1345 ,  1355 . If the time reference pulse t r  has had enough time to propagate to the input of an n th  latch, the input of the n th  latch is low and when clocked, a corresponding low logic level is present as the n th  latch output signal Q n  (where Q n  is representative of the latch output at the n th  stage of the series connection of latches) If the time reference pulse t r  has not had enough time to propagate to the input of the n t h latch, the input of the n th  latch is still at a high logic level, resulting from the level being established during the power up time t 1 . 
         [0074]    The leading edge transition of the time reference pulse t, propagating through the series connection of the delay stages  1310 ,  1320 ,  1330 ,  1340 ,  1350  means that according to position within the series of connections, any given latch captures a level prior to or after the leading edge of the time reference pulse t r  when the given latch is activated. All latches prior to the leading edge transition (topologically in the schematic diagram of  FIG. 13 ) capture a low logic level and all latches subsequent to the leading edge transition capture a high logic level. The latch output signals “Q 0 ”, “Q 1 ”, “Q 2 ”, “Q 3 ”, “Q 4 ” are measured at a measurement time t m  which occurs after a settling time characteristic of the series of latches  1315 ,  1325 ,  1335 ,  1345 ,  1355 . For example, at the measurement time t m , the first three latches  1315 ,  1325 ,  1335  are provided with a low level from a preceding delay stage output signal “A”, “B”, “C”. The first three latch output signals “Q 0 ”, “Q 1 ”, “Q 2 ” at the measurement time tm  1405 ,  1415 ,  1425  are also at a low level. The last two latches  1345 ,  1355  are provided with a high level from a preceding delay stage output signal “D”, “E”. The last two latch output signals“Q 3 ”, “Q 4 ” at the measurement time tm  1435 ,  1445  are also at a high level. 
         [0075]    The latch output signals “Q 0 ”, “Q 1 ”, “Q 2 ”, “Q 3 ”, “Q 4 ”, taken as an ordered sequence, produce a positional value of the trailing edge transition of the time reference pulse t r . With the respective values of the latch output signals “Q 0 ”, “Q 1 ”, “Q 2 ”, “Q 3 ”, “Q 4 ” analyzed as a sequence of values corresponding to the presence or absence of a reference level, a position in time of the time reference pulse t r  within the exemplary time reference device  1300  is determined. For example, the positional value 00011 is produced by the latch output signals “Q 0 ”, “Q 1 ”, “Q 2 ”, “Q 3 ”, “Q 4 ” at the measurement time t m    1405 ,  1415 ,  1425 ,  1435 ,  1445 . The positional value 00011 indicates that the trailing edge of the time reference pulse t, occurred between three and four delays times. The positional value is a magnitude characteristic of the time reference pulse t r  and is usable by internal circuitry (not shown) of a receiver for establishing sampling time characteristics during the calculation time t calc . Key sampling time characteristics so determined are the sample delay time f 1  (t r ) and sample time f 2  (t r ) ( FIG. 12 ). 
         [0076]    An additional sampling time characteristic is the point in a protocol when a transmission phase has ended. A particular transmission termination characteristic is, for example, a stop time f stop  (t r ) (not shown). The stop time f stop  (t r ) of a protocol is also a function of the time reference pulse t r . After a given phase of a transmission concludes either a next phase of transmission follows or the receiver is able to commence a next operation/such as writing of the data just received. For example, to signify to a receiver that a write is possible after address and data are sent, the master does not cause a transition signal, for example, and does not pull the voltage level on the single wire bus to a low level. The receiver waits an amount of time equal to the stop time f stop  (t r ) and samples the bus level. If after the stop time f stop  (t r ) elapses and the level on the bus remains high, the receiver knows that the present transmission phase has concluded and a writing phase may be initiated by the receiver. In a complementary situation, after the stop time f stop  (t r ) elapses and the level on the bus is not high, the receiver knows that the master is commencing a next transmission phase and the receiver must respond accordingly. 
         [0077]    By configuring a magnitude of delay in each of the delay stages  1310 ,  1320 ,  1330 ,  1340 ,  1350  to correspond to an expected range of magnitudes of lime reference pulses t r  to be received, a receiver is able to autonomously determine a rate at which data is transmitted by a master and set sampling time characteristics accordingly to correctly receive data from the master. Essential sampling time characteristics are derivable by a receiver for determining when to initiate sampling, how long to sustain sampling, and when sampling may conclude, thus allowing the receiver to go on to other processes. In this way/a reference time for a single wire protocol and the ensuing essential timing characteristics for sampling data within the protocol are determined. 
         [0078]    Although the detailed description and drawings describe various embodiments and methods for single- and multi-hit circuits for implementing a communication protocol, one skilled in the art will recognize that other embodiments can readily be contemplated without departing from the intended scope of the device described. For example, various types of flip-flops and latches are referenced herein. However, a skilled artisan will recognize that many other combinational logic circuits will have the same effect as components of the present invention. A skilled artisan will recognize that a number of inverter pairs and a value of the capacitor may be selected to accumulate a desired delay of each stage. Additionally, delays may be chosen to be not equal to one another. For example a magnitude of delay between stages may form a progression so that an increasing or decreasing value of delay between successive stages allows for an expansion in the scope of time captured at the measurement time or in the case of decreasing values, forms a finer grain resolution for determining a trailing edge of a reference pulse. One skilled in the art will recognize that a range of magnitudes of time reference pulses will correspond to the selection of magnitudes in each delay stage and any progression assigned to the delay magnitudes. 
         [0079]    Additionally, delay elements are shown as hardware elements implemented with inverters. One of skill in the art will also recognize that other hardware or software changes may be implemented that are still within the scope of the present invention. Therefore, the scope of the present invention shall only be limited by the appended claims.