Abstract:
A configuration of logic elements enables existing Serial-In-Parallel-Out (SIPO) shift registers to perform their own bit count, report the receipt of a valid transmission consisting of an expected number of bits and report the receipt of an invalid transmission consisting of greater than the expected number of bits. Logic elements additional to the foregoing enable SIPO shift registers to receive valid transmissions of varying expected numbers of bits. Special purpose integrated circuits (ICs) are disclosed which also contain the aforementioned configurations of logic elements. Newly designed SIPO shift registers which contain within them the foregoing configurations of logic elements are further disclosed. Potential messages of multiple acceptable message lengths are accommodated. Some embodiments are equipped with tri-state data outputs.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates, in general, to the transmission of binary data between digital devices, and, more particularly, to enabling existing and newly designed serial-in-parallel out (SIPO) shift registers to perform their own bit count, report the receipt of valid transmissions of various expected lengths, and report the receipt of certain invalid transmissions. 
         [0003]    2. Description of Related Art 
         [0004]    Digital data is often transmitted serially between digital devices via a combination of transmitting Parallel-In-Serial-Out (PISO) and receiving SIPO shift registers. It is prudent for a receiving SIPO shift register to report and verify that it has received a valid transmission of some expected number of bits—i.e., a packet or message of a particular, predetermined length. To this end, SIPO shift registers often operate in conjunction with an associated binary counter uniquely designed to report receipt of the expected number of bits of a message transmission. In general, there are several difficulties and shortcomings in current approaches to this requirement. First, there is the need to design a unique counter for each application, dependent on the expected length of transmissions. There is also the need to provide the flip-flops and one or more gates needed to equip the counter, and to report and verify receipt of a transmission of the expected number of bits. This, in turn, requires supplying additional surface area on a printed circuit card in order to mount the counter components. Such additional components increase the power used and heat generated the overall circuitry. Moreover, these additional components increase the amount of printed traces, or circuit wiring, required on a printed circuit card on which all of these components are mounted. 
         [0005]    For certain applications, it may be desirable to send transmissions of varying numbers of expected bits. This raises additional problems. First, this can require adding a second SIPO shift register for the second potential message length, having the same issues described above. 
         [0006]    Accordingly, it is an object of the present invention to supply a single design requiring few components, applicable to SIPO shift registers of any number of bits, that eliminates the need to design a unique associated bit counter for each different expected number of bits transmitted. 
         [0007]    It is another object of the present invention to reduce to a single integrated circuit, or to eliminate the external components required to perform, the bit count and other functions and to enable a SIPO shift register to receive transmissions of more than one expected length. 
         [0008]    It is yet another object of the present invention to reduce the required area of a printed circuit card required to mount the external components associated with a SIPO shift register. 
         [0009]    It is still another object of the present invention to reduce the amount of power used and heat generated, by reducing the number of digital logic components required to perform the counting and other functions commonly associated with a SIPO shift register. 
         [0010]    It is a further object of the present invention to reduce the amount of printed wiring on a printed circuit card incorporating one or more SIPO shift registers. 
         [0011]    It is an additional object of the present invention to eliminate or reduce the need for multiple SIPO shift registers in applications having digital message transmissions of more than one predetermined bit length. 
         [0012]    These and other objects and features of the present invention will become apparent in view of the present specification, drawings and claims. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    In accordance with the several embodiments of this invention, logic components are assembled in configurations that enable existing and newly designed SIPO shift registers to perform their own bit count, report the receipt of valid and/or certain invalid transmissions, and accept transmissions of expected differing lengths. The logic configurations of this invention are developed first in the form of discrete components, secondly in the form of special purpose integrated circuits, and thirdly as part and parcel of newly designed SIPO shift registers. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]      FIG. 1  is schematic diagram of a first embodiment of the present invention; 
           [0015]      FIG. 2  is a schematic diagram of a second embodiment of the present invention; 
           [0016]      FIG. 3  is a schematic diagram of a third embodiment of the present invention; 
           [0017]      FIG. 4  is a timing diagram of the sequential operation of the circuitry of the embodiments of  FIGS. 1-3 . 
           [0018]      FIG. 5  is a schematic diagram of a fourth embodiment of the present invention; 
           [0019]      FIG. 6  is a schematic embodiment of a fifth embodiment of the present invention; 
           [0020]      FIG. 7  is a schematic diagram of an application of the embodiment of  FIG. 6 ; 
           [0021]      FIG. 8  is a timing diagram of the sequential operation of the embodiments of  FIGS. 5 and 6 ; 
           [0022]      FIG. 9  is a schematic diagram of a sixth embodiment of the present invention; 
           [0023]      FIG. 10  is a schematic diagram of a seventh embodiment of the present invention; and 
           [0024]      FIG. 11  is a timing diagram of the sequential operation of the embodiments of  FIGS. 9 and 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    While several different embodiments of the present invention are described herein and shown in the various figures, common reference numerals in the figures denote similar or analogous elements, components or structure amongst the various embodiments. 
         [0026]    A first embodiment  1  of the present invention, in the form of discrete components enabling an existing SIPO shift register to perform its own bit count, report the receipt of transmissions of some valid expected length and report the receipt of certain invalid transmissions of greater than the expected length, is shown in  FIG. 1  as comprising D-type flip-flop FF 0   2 , JK-type master-slave Bad Transmission flip-flop FFBT  3 , inverted active reset signal RST  4 , clock signal CLK  5 , data input (from transmitting circuitry) DATA  6 , D 1  signal  7 , END signal  8 , OK control signal  9 , AND gate G 1   10 , OK signal  11 , Bad Transmission (BT) signal  12 , FFBT K input  13 , tri-state driver  31 , READ command  32 , and D 1 B signal  33 . Flip-flop FF 0   2  is initially preset to a logic 1 value to establish the End of Transmission Marker (ETM). 
         [0027]    Flip-flop FFBT  3  is set whenever an invalid transmission, being too many bits in length, is received, as output and reported by BT signal  12 . In the various embodiments of the present invention, including the embodiment of  FIG. 1 , inverted logic reset signal  4  is employed to reset all circuitry, on both integrated circuits and SPIO shift registers, with the exception of certain components of the fifth, sixth and seventh embodiments of the present invention. Clock signal CLK  5  is the data transmission clock accompanying data input signal DATA  6 , and clocks both flip-flop DDO  2  and flip-flop FFBT  3 . Signal D 1   7  is output from flip-flop FF 0   2 , is initially set to a logic 1 value to establish the End of Transmission Marker (ETM), and finally contains the last bit of the transmitted sequence. END signal  8  signifies receipt of a complete transmission, and is coupled to both the J input of both Bad Transmission flip-flop FFBT  3  and one input of AND gate  10 . The other input of AND gate G 1   10  is OK control signal  9 , output from Bad Transmission flip-flop FFBT  3 . OK control signal  9  selectively enables or cuts off AND gate G 1  and its output, OK signal  11 , which signifies receipt of a valid overall transmission. 
         [0028]    BT signal  12 , output from Bad Transmission flip-flop FFBT  3 , reports the receipt of a bad serial data transmission, composed of too many bits in length. Grounded K input  13  of flip-flop FFBT  3  prevents the resetting of flip-flop FFBT  3  as this flip-flop&#39;s clock input is pulsed. This embodiment is equipped with a tri-state driver for use when the invention is applied to an existing SIPO shift register with tri-state data outputs. In particular, inverting tri-state driver  31 , controlled by READ command  32 , receives the inverted output  34  from flip-flop FF 0   2 , and provides a buffered tri-state output D 1 B  33  having the same logic state as D 1  signal  7 . 
         [0029]    Referring to  FIG. 2 , a second embodiment of the invention, wherein the first embodiment of the invention is incorporated into a special purpose integrated circuit, is shown applied to an arbitrarily selected, existing SIPO shift register  14 . Although, in the example of  FIG. 2 , a 12-bit SIPO shift register is shown, the present invention is capable of operation in conjunction with shift registers of any arbitrary length. The connecting leads between the special purpose integrated circuit  1  and SIPO shift register  14  of  FIG. 2  are as follows: RST signal  4  presets flip-flop FF 0   2  to the logic 1 state, hereby establishing the ETM, and resets flip-flop FFBT  3  and all stages of SIPO shift register  14  to the logic 0 state. If tri-state driver  31  is not used, its READ control signal  32  is coupled to logic ground or is otherwise brought to a logic 0 state. CLK signal  5  clocks incoming data into flip-flop FF 0   2  and advances the ETM and data from flip-flop FF 0   2  to and through SIPO shift register  14 . DATA signal  6  brings in data from the transmitting source. D 1  signal  7  is the Q output of flip-flop FF 0   2  and the means by which the ETM and input data are advanced to the SIPO shift register  14 . Signal D 1   7  also becomes the last bit of data transmitted for a valid transmission. END signal  8  indicates that a valid transmission of the expected number of bits has been received. END signal  8  may be connected to any desired D output along the length of SIPO shift register  14 , thereby selecting for expected transmissions of a length shorter than the physical length of SIPO shift register  14 . 
         [0030]    As shown in  FIG. 2 , CLK signal  5  and inverted active RST signal  4  are coupled to both the circuitry  1  of the first embodiment of the invention, as well as to the clock and reset signals, respectively, of existing SIPO shift register  14 . Signal D 1   7 , output from flip-flop FF 0   2 , is coupled to the D 1  input of existing SIPO shift register  14 . The Q output of the final flip-flop FF 12  of existing SIPO shift register  14  is coupled to END signal  8  of the circuitry  1  of the first embodiment of the invention. 
         [0031]    A newly designed SIPO shift register  15  incorporating the novel features of the present invention is shown in  FIG. 3 . As can be seen, this particular embodiment does not include the tri-state output gate  31 . Moreover, while a 12-bit SIPO shift register incorporating the present invention is shown in  FIG. 3 , shift registers of any arbitrary length may be constructed to include the features of the present invention. In this embodiment, flip-flop FF 0   2  is shown logically positioned at the beginning of the daisy-chained flip-flops FF 2  through FF 12 , and flip-flop FFBT  3  is positioned following flip-flop FF 12   16 . END signal  8  is again derived from the Q output of flip-flop FF 12 . Moreover, while the example of  FIG. 3  does not include a tri-state output driver, all data outputs, D 1  through D 12  may optionally be equipped with tri-state outputs. 
         [0032]    A common timing diagram illustrating the sequential operation of the circuitry of the embodiments shown in  FIGS. 1 through 3  is shown in  FIG. 4 . Referring to  FIG. 4 , preparation for the receipt of a transmission starts when RST signal  4  goes to the logic 0 state, presetting flip-flop FF 0   2  and its Q output D 1   7  to the logic 1 state, thus establishing the ETM and resetting all other flip-flops of SIPO shift registers  14  and  15 , as applicable to the embodiment of the invention being considered. This resetting also resets the END  8  signal and the two-input AND gate G 1   10 , and its output lead OK  11 , to the logic 0 state. 
         [0033]    Transmission begins when the transmitting device has set the first data bit DATA  6  on-line and sends the first clock pulse CLK  5 , thus validating the data. The first CLK  5  pulse clocks new DATA  6  into flip-flop FFO, and advances the ETM from flip-flop FF 0   2  to flip-flop FF 1  of the SIPO shift register,  14  or  15 , as applicable. Successive CLK  5  pulses continue to advance the ETM until it reaches the particular SIPO shift register flip-flop that has been preselected to determine the expected length of transmission (FF 12  of SIPO shift register  14  or  15  in the embodiments illustrated by  FIG. 4 ), where it indicates the receipt of a valid transmission of the expected number of bits. Moreover, in the embodiments illustrated by  FIG. 4 , the output of flip-flop FF 12 , END signal  8 , now in the logic 1 state, is the ETM. At this time inverted Q output signal  9  of flip-flop FFBT  3  is in the logic 1 state. The combination of END signal  8  and inverted Q output signal  9  of flip-flop FFBT  3 , both in the logic 1 state, collectively drive 2-input AND gate GI  10  and its output, OK  11 , to the logic 1 state, thereby reporting the receipt of a valid transmission. The transmitted data is available on output signals D 1   7  through D 12 . The receipt of any additional CLK  5  pulses will drive flip-flop FFBT  3  and its Q output, BT  12 , to the logic 1 state, indicating receipt of a bad transmission consisting of too many bits. The inverted Q output signal  9  of flip-flop FFBT  3  transitions to the logic 0 state, driving two-input AND gate G 1   10  and its output to the logic 0 state, thereby terminating OK signal  11 . Flip-flop FFBT  3 , once set to the logic 1 state, cannot be reset by a successive CLK  5  pulse, inasmuch as its K input  13  is connected to logic ground. 
         [0034]    A fourth embodiment of the present invention, in the form of a special purpose integrated circuit in which additional discrete logic components have been added to the logic configuration of the previously described embodiments, is shown in  FIG. 5 . In this embodiment, the circuitry again enables an existing SIPO shift register to perform the functions afforded by the previously described embodiments, and, additionally, permits the SIPO shift register to receive and report the validity of transmissions of differing expected lengths. 
         [0035]    Referring to  FIG. 5 , this additional circuitry comprises D-type flip-flop FFSEL  17 , AND gate G 2   18 , OR gate G 3   19 , input signal SEL  20 , input signal SHRT  21 , input signal ENDS  8 S, and input signal ENDD  8 D. 
         [0036]    A fifth embodiment of the present invention, in which the discrete components of the fourth embodiment are incorporated in the form of a special purpose integrated circuit  24 , is shown in  FIG. 6 . An illustration of an application of the special purpose integrated circuit  24  of the fifth embodiment of the invention, shown applied to an arbitrarily selected, existing SIPO shift register  25 , is shown in  FIG. 7 . In this embodiment, CLK input  5  and inverted active RST signal  7  are coupled to both integrated circuit  24  and SIPO shift register  25 . Moreover, in the example of  FIG. 7 , ENDS signal  8 S, corresponding to the anticipated short message length of 16 bits, is coupled to output D 17  of SIPO shift register  25 , while ENDD signal  8 D, corresponding to the anticipated default transmission length of 24 bits, is coupled to the Q output of the final flip-flop, FF 24  of SIPO shift register  25 , and occurs automatically if the short ENDS signal  8 S has not been selected. When a valid word has been received in the configuration illustrated, data is available on leads D 1  through D 16  for a short transmission and leads D 1  through D 24  for a long transmission. Signals  8 S and  8 D are shown as dotted lines in  FIG. 7  to illustrate that the specific D outputs of SIPO sift register  25  to which they are presently shown connected are but one option, and that alternative D output connections may alternatively be employed in order to accommodate data transmissions of other expected lengths. As the ENDS signal  8 S and the ENDD signal  8 D must both be made continuously available to special purpose integrated circuit  24 . The SIPO shift register  25  selected for this application cannot have tri-state outputs. 
         [0037]    A common timing diagram illustrating the sequential operation of the circuitry of the embodiments shown in  FIGS. 5 through 7  is shown in  FIG. 8 . Referring to  FIG. 8 , the expected length of a transmission is determined when SHRT signal  21  has been placed in either the logic 1 or the logic 0 state, and flip-flop FFSEL  17  has been set accordingly by a clock pulse on the SEL  20  signal. Flip-flop FFSEL  17  is clocked to either the logic 1 state for a short length data transmission, or to the logic 0 state for a long, or default, length data transmission. Preparation for the receipt of a transmission starts when inverted active RST signal  4  goes to the logic 0 state, presetting flip-flop FF 0   2  and its Q output D 1   7  to the logic 1 state, thus establishing the ETM, and resetting all of the internal flip-flops of both SIPO shift register  25  and special purpose integrated circuit  24 , apart from flip-flop FFSEL  17 . This resetting also resets the END  8 , ENDD  8 D and ENDS  8 S signals and output OK  11  of AND gate G 1   10  to the logic 0 state. 
         [0038]    Transmission begins when the transmitting device has set the first data bit on-line and sends the first clock pulse. The first pulse of CLK signal  5  clocks the first bit of transmitted data on DATA signal  6  into flip-flop FF 0   2  and advances the ETM initially preset into flip flop FF 0   2  to flip flop FF 1  of SIPO shift register  25 . Successive pulses of CLK signal  5  continue to advance the ETM until, in the case illustrated, it advances to flip-flop FF 16  if a short transmission is expected, or flip-flop FF 24  if a longer, default-length transmission is expected. Moreover, in the case illustrated, either the output of flip-flop FF 16 , generating the ENDS signal  8 S for a short transmission, or the output of flip-flop FF 24 , generating the ENDD signal  8 D lead for a default length transmission, transitioning to the logic 1 state, indicates the end of the expected transmission. Either indication, when occurring, will be passed to the END signal  8  by two-input OR GATE G 3   19 , indicating receipt of a transmission having an expected length. At this time, inverted Q output  9  of flip-flop FFBT  3  is in the logic 1 state. At this time, the combination of END signal  8  and inverted Q output  9  of flip-flop FFBT  3 , both in the logic 1, state drives two-input AND gate G 1   10  and its output, OK signal  11 , to the logic 1 state, thereby reporting the receipt of a valid transmission. At the same time, the transmitted word, having been converted to parallel form, is available on signals D 1   7  through D 16  of SIPO shift register  25  for a short transmission, or signals D 1   7  through D 24  for a default length transmission. 
         [0039]    Receipt of any additional CLK  5  pulses following the end of a valid transmission will drive flip-flop FFBT  3  and its Q output, BT signal  12 , to the logic 1 state, thereby indicating receipt of a bad transmission consisting of too many bits. At the same time, the inverted Q output  9  of flip-flop FFBT  3  transitions to the logic 0 state, which drives the two-input AND gate G 1   10  and its output to the logic 0 state, thereby terminating the OK signal  11 . As its K input  13  is connected to logic ground, flip-flop FFBT  3 , once set to the logic 1 state, cannot be reset by additional pulses of CLK signal  5 . 
         [0040]    A sixth embodiment of the present invention, in which the circuitry of the special purpose integrated circuit of the fifth embodiment is incorporated within a newly designed SIPO shift register  28  that may be applied to data transmissions having differing expected lengths through the use of variable external connections, is shown in  FIG. 9 . Signals  8 S and  8 D are shown as dotted lines in  FIG. 9  to illustrate that the specific D outputs of SIPO sift register  28  to which they are presently shown connected are but one option, and that alternative D output connections may alternatively be employed in order to accommodate data transmissions of other expected lengths. Unlike the embodiment of  FIG. 7 , however, this external wiring of signals  8 S and  8 D is entirely coupled to a single integrated circuit  28 , as opposed to wiring between a special purpose integrated circuit and an existing SIPO shift register. Moreover, while short and default message transmission lengths of 16 and 24 bits, respectively, are depicted within  FIG. 9 , alternative message lengths may alternatively be wired by coupling these signals to desired D outputs of SIPO shift register  28 . 
         [0041]    A seventh embodiment of the present invention, in which the circuitry of the special purpose integrated circuit of the fifth embodiment is incorporated within a newly designed SIPO shift register  29  having internally wired, pre-configured short and default message length values, is shown in  FIG. 10 . Moreover, while short and default message transmission lengths of 16 and 24 bits, respectively, are depicted within  FIG. 10 , alternative message lengths may alternatively be wired by internally wiring these signals to desired D outputs of SIPO shift register  29 . The use of internal connections for signals  8 S and  8 D permit tri-state drivers to alternatively be included to the D outputs of SIPO shift register  29 . 
         [0042]    Both of the sixth and seventh embodiments perform their own received bit count, issue an OK signal  11  signal when a valid transmission is received, issue a BT signal  12  when a bad transmission consisting of too many bits is received, and can receive transmissions of two different expected lengths. Additional selection components may optionally be added in order to allow receipt of transmissions of a greater number of different lengths (i.e., three valid transmission lengths, four valid transmission lengths, etc.). 
         [0043]    A common timing diagram illustrating the sequential operation of the circuitry of the embodiments shown in  FIGS. 9 and 10  is shown in  FIG. 11 . The expected length of a transmission is determined when SHRT signal  21  has been placed in either the logic 1 or the logic 0 state, and flip-flop FFSEL  17  has been set accordingly by a pulse SEL signal  20 . Specifically, Flip-flop FFSEL  17  is clocked to the logic 1 state for a short anticipated data transmission length, or to the logic 0 state for a long, or default length data transmission. Preparation for the receipt of a transmission starts when the inverted active RST signal  4  goes to the logic 0 state, presetting flip-flop FF 1   27  and its Q output D 1   7  to the logic 1 state, thus establishing the ETM and resetting all other flip-flops of the SIPO shift registers  28 ,  29 , except for flip-flop FFSEL  17 , which is not affected by RST signal  4 . This resetting also resets ENDS signal  8 S, ENDD signal  8 D, and END signal  8 , and drives two-input AND gate G 1   10  and its output OK signal  11  to the logic 0 state. 
         [0044]    Transmission begins when the transmitting device has set the first data bit on-line and sends the first clock pulse, CLK signal  5 , which clocks new DATA  6  into flip-flop FF 1   27 , and advances the ETM preset into flip-flip FF 1   2  of the applicable SIPO shift register,  28  or  29 . Successive pulses of CLK signal  5  continue to advance the ETM until the fifteenth pulse advances it, in the cases illustrated, to flip-flop FF 16  of SIPO shift register  28  or  29  for a transmission of short expected length, or until the twenty-third pulse advances the ETM to flip-flop FF 24  of SIPO shift register  28  or  29  for a transmission of the longer, default expected length. When flip-flop FFSEL  17  has been set to a logic 1 for a transmission of short expected length and flip-flop FF 16  of SIPO shift register  28  or  29  contains the ETM, the ETM is sent via ENDS signal  8 S to two-input AND gate G 2   18 . With Q output  22  of flip-flop FFSEL  17  and ENDS signal  8 S both in the logic 1 state, two-input AND gate G 2   18  and its output  23  go to the logic 1 state, and a logic 1 is sent to and is passed by two-input OR gate G 3   19  via its output  30  to the D input of flip-flop FFOK  16 . The sixteenth pulse of CLK signal  5  will set flip-flop FFOK  16  to the logic 1 state, setting its Q output  8  to the logic 1 state. At this time, flip-flop FFBT  3  is in the logic 0 state. The combination of Q output  8  of flip-flop FFOK  2  and the inverted Q output  9  of flip-flop FFBT  3  both in the logic 1 state, drives two-input AND gate G 1   10  and its output signal OK  11  to the logic 1 state, thereby indicating receipt of a valid transmission of expected length. When flip-flop FFSEL  17  has been set to a logic 0 for an anticipated data transmission of a long, or default expected length, and the ETM has been advanced until flip-flop FF 24  of SIPO shift register  28  or  29  contains the ETM, the ETM is sent via ENDD signal  8 D to two-input OR gate G 3   19  and is passed via its output signal  30  to the D input of flip-flop FFOK  16 . The twenty-fourth pulse of CLK signal  5  will set flip-flop FFOK  16  to the logic 1 state, likewise setting its Q output  8  to the logic 1 state. At this time, flip-flop FFBT  3  is in the logic 0 state. The combination of the Q output  8  of flip-flop FFOK  2  and the inverted Q output  9  of flip-flop FFBT  3 , both in the logic 1 state, drives two-input AND gate G 1   10  and its output signal OK  11  to the logic 1 state, indicating receipt of a valid transmission having an expected length. 
         [0045]    Receipt of any additional pulses of CLK signal  5  in excess of sixteen, for a transmission of short expected length, or in excess of twenty-four, for a transmission of long, or default expected length, will drive flip-flop FFBT  3  and its Q output, BT signal  12 , to the logic 1 state, indicating receipt of a bad transmission consisting of too many bits. Inverted Q output  9  of flip-flop FFBT  3 , now in the logic 0 state, drives the two-input AND gate G 1   10  and its output, OK signal  11 , to the logic 0 state, terminating OK signal  11 . Flip-flop FFBT  3 , once set to the logic 1 state, cannot be reset by additional pulses of LK signal  5 , as its K input  13  is connected logic ground. 
         [0046]    Several specific embodiments of the present invention have been illustrated. However, there are many ways to implement the invention due to the various possible combinations of available logic elements that can be configured to achieve the same results. The circuits can be implemented using any of a multitude of technologies, such as RTL, DTL, CMOS, PMOS, NMOS, ECL, TTL, LSTTL or discrete components, such as resistors, transistors, diodes, etc.