Abstract:
The present invention provides a circuit for writing a particular sized data word from a common input to a number of individual memory cells in a memory array and reading a particular sized data word from the individual memory cells to a common output. The size of the word written to the memory cells can be larger, smaller or the same as the size of the word read from the memory array. The present invention uses a multi-bit write counter to distribute a write timing signal to a number of multiplexer blocks and a multi-bit read counter to distribute a read timing signal to a number of sense amplifier blocks. Each of the multiplexer blocks receives both a data input signal from the common input and the write timing signal continuously when the circuit is in operation. Each of the sense amplifier blocks receives data from the memory array and a read timing signal at all times. When a particular read timing signal is present at a sense amplifier, the output signal containing a fixed width data word is received from one or more of the corresponding memory arrays and is presented to the common output. The present invention reduces the number of internal signal lines necessary to implement the control function and allows for easy modification to both read and write multiple width words to and from the memory array.

Description:
FIELD OF THE INVENTION 
     The present invention relates to FIFO buffers generally and, more particularly, to a clocking scheme for allowing a contiguous memory array to be used to read and write various width data words from a memory array. 
     BACKGROUND OF THE INVENTION 
     A first-in first-out(FIFO) buffer reads various size data words from a memory array and writes various size data words to a memory array. In previous approaches a shift register scheme is generally required to generate a number of intermediate signals necessary to read or write a fixed data word width into the memory array. To implement a clocking scheme that retrieves fixed width data words that are equal to the width of the individual cells in the FIFO memory array, a 16-bit shift register would be required. To extend the previous approach to a memory array that is twice as wide as the width of the output data word, a 32-bit shift register would be required. Specifically, a 32-bit shift register would be necessary for a 9-bit word design and a 16-bit shift register would be required for a 18-bit word design. Previous approaches did not allow a single shift register to be used for both the 9-bit and 18-bit devices. Previous approaches for implementing FIFOs used a “carousel” type data retrieval scheme that used a 16-bit shift register to directly control each of the section control signals. To extend the previous approach systems to read both a 9-bit and 18-bit word would require a 32-bit shift register. The implementation of a 32-bit shift register would cause extreme difficulty in routing the various signals to appropriately connect the outputs of the shift register to each of the section control blocks. The implementation of a 32-bit shift register would also consume more than twice the amount of chip area as compared to a 16-bit shift register. Similar shift register implementations would be required to write data to the memory array. 
     Referring to FIG. 1, one scheme  10  for reading multiple width digital words from a memory array is shown. The scheme  10  generally comprising a shift register  12 , a set of sense amplifiers  14   a ,  14   b ,  14   c  and  14   d  and a set of memory arrays  16   a ,  16   b ,  16   c  and  16   d . A single data output  18  represents an output that receives information presented from each of the sense amplifiers  14   a - 14   d . The 16-bit shift register  12  presents one of a set of control inputs  20   a ,  20   b ,  20   c  and  20   d  to each of the sense amplifiers  14   a - 14   d . When one of the control inputs  20   a - 20   d  are present at one of the sense amplifiers  14   a - 14   d , the information presented to the data output  18  is received from the appropriate memory array  16   a - 16   d . An individual control input  20   a - 20   d  is required for each of the memory arrays  16   a - 16   d . As the number of memory arrays  16   a - 16   d  increases, the number of control inputs  20   a - 20   d  will also increase. Each of the control inputs  20   a - 20   d  need to be individually routed from the individual sense amplifiers  14   a - 14   d  to the shift register  12 . The routing necessary to appropriately connect the control inputs  20   a - 20   d  between the shift register  12  and the sense amplifiers  14   a - 14   d  increases. To expand the shift register  12  to a 32-bit shift register would require twice the amount of routing as well as an increased amount of chip real estate. The increase in routing the control inputs  20   a - 20   d  and the increased chip area makes the previous scheme difficult to implement with multiple width data words. This problem is further discussed in co-pending application Ser. No. 08/584,530, hereby incorporated by reference in its entirety. 
     Referring to FIG. 2, a scheme  22  for writing multiple width digital words to a memory array is shown generally comprising a shift register  24 , a set of multiplexers  26   a ,  26   b ,  26   c  and  26   d  and a set of memory arrays  28   a ,  28   b ,  28   c  and  28   d . A single data input  30  presents an input to each of the multiplexers  26   a - 26   d . The 16-bit shift register  24  presents one of a set of control inputs  32   a ,  32   b ,  32   c  and  32   d  to each of the multiplexers  26   a - 26   d . When one of the control inputs  32   a - 32   d  is present at one of the multiplexers  26   a - 26   d , the data input  30  is received and is written to the appropriate one of the memory arrays  28   a - 28   d . Individual control inputs  32   a - 32   d  are required for each memory array  28   a - 28   d . As the number of memory arrays  28   a - 28   d  increases, the number of control inputs  32   a - 32   d  will also increase. Each of the control inputs  32   a - 32   d  would need to be individually routed from the individual multiplexers  26   a - 26   d  to the shift register  24 . The routing necessary to appropriately connect the control inputs  32   a - 32   d  between the shift register  24  and the multiplexers  26   a - 26   d  increases. To expand the shift register  24  to a 32-bit shift register would require twice the amount of routing as well as an increased amount of chip real estate. The increase in routing the control inputs  32   a - 32   d  and the increased chip area makes the previous approach difficult to implement with multiple width data words. This problem is also addressed in co-pending application Ser. No. 08/559,983, hereby incorporated by reference in its entirety. 
     It is desirable to receive a particular size data word from the data input  30 , write the word into the memory array  28   a - 28   d , read a different size data word from the memory array  28   a - 28   d  and then present the different sized word to the data output  18 . The schemes  10  and  22  do not contemplate this multiple size word writing and reading. In particular, the chip real estate problems inherent in implementing the shift register  12  and the shift register  24  would be magnified when implementing a system that writes in a particular size digital word and reads out a different size digital word. Additionally, logic would be necessary to synchronize the writing and reading from the memory arrays  16   a - 16   c  or the memory arrays  28   a - 28   d . It should be noted that the memory arrays  16   a - 16   c  in FIG. 1 would correspond to the memory arrays  28   a - 28   d  in FIG. 2 for a system that writes and reads different sized words. 
     SUMMARY OF THE INVENTION 
     The present invention provides a clocking scheme for receiving a particular sized data word from a common input, writing the word to a number of individual memory cells in a memory array, reading another particular sized data word from the individual memory cells and then presenting the data word to a common output. The size of the word written to the memory cells can be larger, smaller or the same as the size of the word read from the memory array. The present invention uses a multi-bit write counter to distribute a write timing signal to a number of multiplexer blocks and a multi-bit read counter to distribute a read timing signal to a number of sense amplifier blocks. Each of the multiplexer blocks receives both a data input signal from the common input and the write timing signal at all times. When a particular write timing signal is present at the multiplexer, the fixed width data input is presented to the corresponding memory array. Each of the sense amplifier blocks reads data from the memory array and receives a read timing signal at all times. When a particular read timing signal is present at a sense amplifier, the output signal containing a fixed width data word is read from one or more of the corresponding memory arrays and is presented to the common output. The present invention reduces the number of internal signal lines necessary to implement the control function and allows for easy modification to both read and write multiple width words from the memory array. 
     The objects, features and advantages of the present invention include providing a control circuit for distributing data to a number of memory arrays from a common input, reading data from a number of memory arrays and presenting the data to a common output for use with both synchronous and asynchronous FIFOs as well as other memory devices. The present circuit produces the distributing and reading effects using a minimum number of signal lines and eliminates the need to use wide bit shift registers. Thus, the present invention consumes less overall chip real estate. The present circuit can also be very easily adapted to larger or smaller memory organization systems with minimum design changes and can easily be adapted to denser and wider memory devices with multiple data input and output word widths. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the present invention will be apparent from the following detailed description and the appended claims in which: 
     FIG. 1 is a block diagram of a reading scheme, 
     FIG. 2 is a block diagram of a writing scheme; 
     FIG. 3 is a block diagram of a preferred embodiment of a present invention; 
     FIG. 4 is a timing diagram illustrating the effects of the present invention using a 9-bit data word; and 
     FIG. 5 is a timing diagram illustrating an implementation of the present invention using an 18-bit data word. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 3, a block diagram of a clocking circuit  40  is shown in accordance with a preferred embodiment of the invention. The clocking circuit  40  generally comprises a data input  42 , a write counter  44 , a set of decoder and multiplexers  46   a ,  46   b ,  46   c  and  46   d , a set of memory arrays  48   a ,  48   b ,  48   c  and  48   d , a set of sense amplifiers  50   a ,  50   b ,  50   c  and  50   d , a read counter  52 , and a data output  54 . The sense amplifiers  50   a - 50   d , which act as output devices or means for outputting data, can also be implemented as latches or any other device that provides the equivalent function(s) of sensing and/or amplifying an electrical potential. Each of the decoder and multiplexers  46   a - 46   d  have a write timing input  56   a - 56   d  and a signal input  58   a - 58   d . The decoder and multiplexers  46   a - 46   d  act as receiving devices which provide a means for receiving data and preferably sending the data to a memory device, such as a decoder, a decoder and multiplexer or other device(s) providing equivalent function(s). The write timing input  56   a - 56   d  of each of the decoder and multiplexers  46   a - 46   d  receive a write timing signal from the write counter  44  continuously when the circuit  40  is in operation. The signal input  58   a - 58   d  of each of the decoder and multiplexers  46   a - 46   d  receives a digital word from the data input  42  continuously when the circuit  40  is in operation. One or more the decoder and multiplexers  46   a - 46   d  will write a digital word to the corresponding memory array  48   a - 48   d  when a particular timing signal is received at the appropriate write timing input  56   a - 56   d . The write timing input  56   a - 56   d  of each of the decoder and multiplexers  46   a - 46   d  is received through a write timing bus  64 . 
     Each of the sense amplifiers  50   a - 50   d  has a signal input  60   a - 60   d  and a read timing input  62   a - 62   d . Each of the sense amplifiers  50   a - 50   d  reads a digital word from the corresponding memory array  48   a - 48   d  continuously when the circuit  40  is in operation. Each of the read timing inputs  62   a - 62   d  of the sense amplifiers  50   a - 50   d  receive a read timing signal from the read counter  52  continuously when the circuit  40  is in operation. One or more of the sense amplifiers  50   a - 50   d  will present a signal to the data output  54  when an appropriate read timing signal is received at one of the read timing inputs  62   a - 62   d . The read timing input  62   a - 62   d  of each of the sense amplifiers  50   a - 50   d  is received from the read counter  52  through a read timing bus  66 . 
     While each of the decoder and multiplexers  46   a - 46   d  will receive the particular signal input  58   a - 58   d  continuously when the circuit  40  is in operation, only certain specific decoder and multiplexers  46   a - 46   d  will respond to the particular write timing signal received at the write timing inputs  56   a - 56   d  at any given time. The decoder and multiplexers  46   a - 46   d  that receive data from the signal inputs  58   a - 58   d  and present information to the corresponding memory arrays  48   a - 48   d  at a particular time are determined by a signal present at the write timing inputs  56   a - 56   d . Each of the decoders and multiplexers  46   a - 46   d  receive the write timing signal at the write timing inputs  56   a - 56   d  continuously when the circuit  40  is in operation. The write counter  44  produces the write timing signal that is a unique multi-bit digital word that changes with each clock cycle. The write counter  44 , when implemented as a 4-bit counter, produces a 4-bit digital word that produces 2 4 , or 16, unique states. A 5-bit write counter  44  produces a 5-bit digital word that produces 2 5 , or 32, unique states. As a result, the addition of a single bit to the write counter  44  and the timing bus  64  doubles the capabilities of the write portion of the clocking circuit  40 . Each unique state produced by the write counter  44  provides a specific write timing signal that only certain specific decoder and multiplexers  46   a - 46   d  will recognize. 
     Each of the sense amplifiers  50   a - 50   d  receive the read timing signal at the read timing inputs  62   a - 62   d  continuously when the circuit  40  is in operation. Similar to the decoder and multiplexers  46   a - 46   d , the sense amplifiers  50   a - 50   d  will receive the signal input  60   a - 60   d  continuously when the circuit  40  is in operation. Only certain specific sense amplifiers  50   a - 50   d  will respond to a specific read timing signal at any given time. The sense amplifier  50   a - 50   d  that reads data from the signal input  60   a - 60   d  from the corresponding memory array  48   a - 48   d  and presents it to the data output  54  is determined by read timing signal present at the read timing input  62   a - 62   d . The read timing inputs  62   a - 62   d  receive the read timing signals from the read counter  52  through the read timing bus  66 . Each of the sense amplifiers  50   a - 50   d  receive the read timing signal at the read timing input  62   a - 62   d  continuously when the circuit  40  is in operation. The read counter  52  produces the read timing signal that is a unique multi-bit digital word that changes with each clock cycle. The read counter  52 , when implemented as a 4-bit counter, produces the read timing signal that is a 4-bit digital word that produces 2 4 , or 16, unique states. A 5-bit read counter  52  produces a 5-bit digital word that produces 2 5 , or 32, unique states. As a result, the addition of a single bit to the read counter  52  and the read timing bus  66  doubles the capabilities of the read portion of the clocking circuit  40 . Only certain specific sense amplifiers  50   a - 50   d  will respond to a specific read timing signal produced by the read counter  52 . 
     A specific example of a particular implementation of the present invention will be described where the memory arrays  48   a - 48   d  are 9-bit wide devices, the data input  42  is a stream of 9-bit digital words, and the data output  54  is a stream of 18-bit digital words. A first word is received by the decoder and multiplexer  46   a  from the data input  42  and written to the memory array  48   a . The decoder and multiplexers  46   b ,  46   c  and  46   d  connected to the memory arrays  48   b ,  48   c  and  48   d  have a write timing signal present at the timing inputs  56   b ,  56   c  and  56   d  and a stream of digital words present at the signal inputs  58   b ,  58   c  and  58   d , but do not write the digital word to the memory arrays  48   b ,  48   c  and  48   d . When the first digital word is completely loaded through the decoder and multiplexer  46   a  and written to the memory array  48   a , the write timing signal will continue to be recognized at the signal input  56   a . The timing signal will then change and be recognized at the signal input  56   b . At this point a second digital word received from the data input  42  will be loaded through the decoder and multiplexer  46   b  and written to the memory array  48   b . The decoder and multiplexers  46   a ,  46   c  and  46   d  will not write the next digital word to the memory arrays  48   a ,  48   c  and  48   d  during this time. A similar word writing is accomplished when the decoder and multiplexer  46   c  and  46   d  write data words to the memory arrays  48   c  and  48   d.    
     In order to read a stream of 18-bit digital words from the memory arrays  48   a - 48   d , two of the sense amplifiers  50   a - 50   d  will simultaneously recognize a particular read timing signal present at the read timing input  62   a - 62   d . For example, the sense amplifiers  50   a  and  50   b  may recognize a particular read timing input on a first clock cycle. This will allow an 18-bit word to be presented at the data output  54 . On the next timing cycle, the sense amplifiers  50   c  and  50   d  will each read a 9-bit half of the next 18-bit digital word that is presented to the data output  54 . On the next clock cycle, the sense amplifiers  50   a  and  50   b  will again be activated. It should be noted that the paring of the sense amplifiers  50   a - 50   d  can be modified to fit the design criteria of a particular application. For example, the first 18-bit digital word can be read from sense amplifier  50   a  and  50   c , while the next 18-bit digital word may be read from the sense amplifiers  50   b  and  50   d . Any such paring may be implemented. 
     It should be noted that each of the memory arrays  48   a ,  48   b ,  48   c  and  48   d  have a corresponding sense amplifier  50   a ,  50   b ,  50   c  and  50   d . Each of the sense amplifiers  50   a - 50   d  recognize only a specific multi-bit read timing signal present at the read timing inputs  62   a - 62   d . Only particular specified sense amplifiers  50   a - 50   d  recognizes the specific multi-bit timing word at any given clock cycle and processes the digital word present at the particular signal input  60   a - 60   d . Effectively, each of the sense amplifiers  50   a - 50   d  act as a digital valve. The digital valve effect of the sense amplifiers  50   a - 50   d  effectively opens when the proper multi-bit timing word is present at a particular read timing input  62   a - 62   d , reading from the appropriate memory array  48   a - 48   d  and presenting the information to the data output  54 . Each of the sense amplifiers  50   a - 50   d  works in combination to completely load a digital word from one of the memory arrays  48   a - 48   d  on a given clock cycle before the next digital word from the next memory array  48   a - 48   d  is loaded into the data output  54  at the next clock cycle. The order that the digital words are received from the memory arrays  48   a - 48   d  can be any order necessary to fit the design criteria of a particular application. 
     The example illustrated using the 9-bit memory arrays  48   a - 48   d  and the 9-bit digital words as the data input  42  has a one word per timing signal relationship for the write portion of the clocking circuit  40 . The read portion illustrated, where a 18-bit word is read from a series of 9-bit memory arrays  48   a - 48   d  has a two word per timing signal relationship, or a double word width. In an application where the width of the digital word is a multiple of the width of the memory arrays  48   a - 48   d , each fraction (i.e. one half, one third, one fourth, etc.) of the digital word would be read from a separate one of the memory arrays  48   a - 48   d  on each clock cycle. As a result, the present invention would read a multi-width digital word from the memory arrays  48   a - 4   d  wherein multiple sense amplifiers  50   a - 50   d  respond to a particular read timing signal. 
     It is generally advantageous for a manufacturer to produce the smallest number of components necessary to maintain all product lines in current production. As a result, from a practical aspect, the present invention would be implemented using a write counter  44  and a read counter  52  that is five-bits wide for all applications that require either 16 unique states or 32 unique states. If only 16 unique states are required for a particular design application, only four of the bits on the write counter  44  or the read counter  52  would be used with one of the bits being disabled. For example, the most significant bit would be disabled if the write counter  44  or the read counter  52  were implemented as an up counter. Other counters could be used that produce a unique state at each clock cycle, such as a random counter. The approach of providing additional bits in the write counter  44  or the read counter  52  is practical since the addition of an additional counter bit and counter output signal line would be less expensive than producing two separate parts. This is in contrast to the previous approaches where two or more 32-bit shift registers are far more difficult to manufacture than two or more 16-bit shift registers. To maintain a single component using previous techniques, the much more complex 32-bit shift registers would have to be produced on each device, even if only a 16-bit shift register portion is actually used. 
     Referring to FIG. 4, a timing diagram illustrating the functioning of the present invention when operating with a series of 9-bit data words as an input is shown. It should be appreciated that the example illustrated in FIG. 4 uses a 9-bit digital word for illustrative purposes only. Any fixed width digital word, including a single bit word, can be used without departing from the spirit of the invention. FIG. 4 generally comprises a WCLK clock  70 , a dlatA signal  72 , a dlatB signal  74 , a dlatC signal  76  and a dlatD signal  78 . The dlatA, dlatB, dlatC and dlatD signals  70 ,  72 ,  74 ,  76  and  78  provide pulses that represent when a word is written to a corresponding memory array  48   a - 48   d . The digital high portions of the WCLK clock  70  are shown as pulses  81 ,  82 ,  83 ,  84 ,  85 ,  86 ,  87  and  88 . 
     When the WCLK clock  70  is high at pulse  81 , the dlatA signal  72  is shown as being high at a pulse  91 . This writes a full 9-bit digital word to the memory array  48   a . When the WCLK clock  70  is high at the pulse  82 , the dlatB signal  74  is shown as being high at pulse  92 . When the WCLK clock  70  is shown as being high at the pulse  83 , the dlatC signal  76  is shown as being high at a pulse  93 . Similarly, when the WCLK clock  70  is shown as being high at the pulse  84 , the dlatD signal  78  is shown as being high at a pulse  94 . The pulses  91 ,  92 ,  93  and  94  represent the writing of a 9-bit digital word to a respective one of the memory arrays  48   a ,  48   b ,  48   c  and  48   d . After the dlatD signal  78  writes a word shown as the pulse  94 , the next data word is written to the memory array  48   a  when the dlatA signal  72  is high at a pulse  95 . A similar effect is shown with a pulse  96 , a pulse  97  and a pulse  98 . A direct relationship is shown where a single word is written to the memory array  48   a , then a single digital word is written to the memory array  48   b , then a single digital word is written to the memory array  48   c  and finally a single digital word is written to the memory array  48   d . After the digital word is written to the memory array  48   d , the process starts again with writing a digital word to the memory array  48   a . The sequential writing of the memory arrays  48   a , then  48   b , then  48   c , is for illustrative purposes only. 
     It should be appreciated that the number of memory arrays  48   a - 48   d  is shown to be four for illustrative purposes only. The number of memory arrays  48   a - 48   d  can be extended to any number of memory arrays desired for a particular design application or can be reduced to a single memory array. Increasing or decreasing the number of memory arrays  48   a - 48   d  would only require replacing the write counter  44  with a counter having a sufficiently wide bit path to provide a sufficient number of independent states to accommodate the number of words written to the number of memory arrays  48   a - 48   d  that are implemented. The width of the bit path would be determined by the width of the digital word, the width and number of the memory arrays  48   a - 48   d  and the desired order of the writing of the memory arrays  48   a - 48   d . To accommodate these adjustments, the width of the bit path may have to be increased, decreased or left unchanged. The order of the writing to the memory arrays  48   a - 48   d  can be any order necessary to fit the design criteria of a particular application. The sequential writing to the memory array  48   a , then  48   b , then  48   c , etc., is for illustrative purposes only. The order of which memory arrays  48   a   14   d  are written to can be adjusted to fit the design criteria of a particular application by programming the decoders and multiplexers  46   a   14   d  to respond to a timing signal that produces a non-sequential writing of the memory arrays  48   a   14   d.    
     Referring to FIG. 5, an 18-bit data word width implementation of the read portion of the present invention is illustrated. It should be appreciated that an 18-bit digital word is read from the memory arrays  48   a - 48   d  while a 9-bit digital word is written into the memory arrays  48   a - 48   d . Other word widths can be implemented at either the data input  42  or the data output  54  to fit the design criteria of a particular application. The 18-bit data word is considered a double width digital word as compared to the width of the memory arrays  48   a - 48   d . Any multiple of the width of the memory arrays  48   a - 48   d  can be used. FIG. 5 generally comprises a RCLK clock  100 , a slatA signal  102 , a slatB signal  104 , a slatC signal  106  and a slatD signal  108 . The data word is 18-bits wide and the individual memory arrays  48   a - 48   d  are 9-bits wide. The 18-bit digital word is comprised of a number of fractional portions read from two of the memory arrays  48   a - 48   d . The digital high portions of the RCLK clock  100  are shown as pulses  111 ,  112 ,  113 ,  114 ,  115 ,  116 ,  117  and  118 . 
     When the RCLK clock  100  is high at the pulse  111 , a first fraction, or half, of a 18-bit digital word is read from the memory array  48   a  and is shown as a pulse  121  on the slatA signal  102 . A second fraction, or half, of the 18-bit digital word is read from the memory array  48   b  and is shown as the slatB signal  104  as a pulse  122 . When the RCLK clock  100  is high at the pulse  112 , a first fraction, or half, of the next 18-bit digital word is read from the memory array  48   c  as shown on the slatC signal  106  as a pulse  123 . The second fraction, or half, of the next 18-bit digital word is read from the memory array  48   d  as shown on the slatD signal  108  at a pulse  124 . When the RCLK clock  100  is high at the pulse  113 , a first fraction, or half, of the next 18-bit digital word is read from the memory array  48   a  as shown as pulse  125  of the slatA signal  102 . A second fraction, or half, of the next 18-bit digital word is read from the memory array  48   b  as shown by the pulse  126  on the slatB signal  104 . A series of pulses  127 ,  128 ,  129 ,  130 ,  131 ,  132 ,  133 ,  134 ,  135  and  136  show similar reading of 18-bit digital words between either the slatA signal  102  and slatB signal  104  or the slatC signal  106  and the slatD signal  108 . Each of the pulses  121 - 136  illustrates a 9-bit half of an 18-bit digital word read from one of the 9-bit wide memory arrays  48   a - 48   d . The order of which memory arrays  48   a - 48   d  are read from can be adjusted to fit the design criteria of a particular application by programming the sense amplifiers  50   a - 50   d  to respond to a timing signal that produces a non-sequential reading of the memory arrays  48   a - 48   d.    
     The example of the present invention illustrated in FIGS. 4 and 5 can be extended to reading and writing larger or smaller width digital words. While the FIG. 5 illustration was limited to reading a double width digital word, a triple, quadruple or other width digital word could be accomplished by extending the plurality of fractional portions of the digital word accordingly. The clocking circuit  40  can be programmed to read any multiple width digital word or write any multiple width digital word. The clocking circuit  40 , for example, may be used to receive 18-bit words from the data input  42  and then 9-bit words to the data output  54 . Additionally, the width of the memory arrays can be a fractional portion of the smallest word either written to or read from the memory arrays  48   a - 48   d . If a 8-bit word is written to the memory arrays  48   a - 48   d  and a 16-bit word is read from the memory arrays  48   a - 48   d , the memory arrays can be 4-bits wide. A combination of a first memory array, (e.g., memory array  48   a ) being 3-bits wide and a second memory array, (e.g., memory array  48   b ) being 5-bits wide will work as well. In other words, the width of the memory arrays  48   a - 48   d  do not have to be equal fractional portions of the smallest word widths. The programming of how the memory array is written to and read from can be programmed either during production of the clocking circuit  40 , after production by using an external device to program the clocking circuit  40  or by any other programming scheme contemplated. Larger or smaller width memory arrays  48   a - 48   d  could also be accommodated. Also, a larger or smaller number of memory arrays  48   a - 48   d  could also be included. In any of the above modifications, the size of the write and read counters  44  and  52  would have to be adjusted accordingly. This adjustment would be minor since the addition of a single bit to the counter  34  doubles the number of possible independent states. 
     The present invention may be implemented as a data interface between systems which exchange data of the same or different bit sizes at the same or different rate. Such systems may include, but are not limited to, networking hardware, a modem, a facsimile machine, a disk drive buffer, a peripheral-computer interface, etc. 
     While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.