JPH03100851A - Fifo storage device - Google Patents

Abstract

PURPOSE:To store the same continuous n-word data in a storage area of (n) words or less by controlling a writing pointer via a comparator and controlling a reading pointer via a 2nd counter where the value read out of a word number field part of a storage element is set as the initial value. CONSTITUTION:A comparator 5 compares the data on a 1st latch 4 which holds temporarily the latest data to be written with the data inputted from outside. When the coincidence is obtained between both data, a coincidence detection signal is inputted through an inverter 7 as the control input of a writing pointer 2. Then the control input is copied to a 2nd latch 8 from a data field part of a storage element 20 as well as to a 2nd counter 9 from a word number field part based of the addresses designated by a reading pointer 3 respectively. The counter 9 is decreased by a read request signal CLK and the latch 8 outputs the data to the outside with the signal CLK. Thus just a signal storage area of (n) words or less suffices when the same data of (n) words are continuously written.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a first-in, first-out storage device used as a buffer memory during data transfer between multiple processors or between multiple buses. An example of the configuration of a conventional first-in first-out storage device is shown in FIG. 10 (Friend) A two-port storage element with a write port and a read port, a write pointer consisting of a counter that increases by LIHll,
A write address for writing data to the storage element IO is generated. 12j & write pointer 1
A read pointer consisting of a counter similar to 1,
Generates a read address when reading data from storage element 1O Write pointer 1 ■ Friend storage element 10
The read pointer 12 is incremented every time a write operation is performed, and even if the address to which data should be written next is specified, the read pointer 12 is also incremented every time a read operation is performed, and the next data to be read is stored. Even if an address is specified, the write pointer 11 and the read pointer 12 match in the initial state where no valid data is stored in the storage element 10, and when data is stored, the write pointer 11 becomes more than the read pointer 12. If the write pointer 11 and the read pointer 12 match after the write operation, the storage element 10 is filled with valid data.With the above configuration, the data written first is written first. However, even if a first-in, first-out storage device capable of reading data is realized, the problem to be solved by the invention is that the above configuration does not solve the problem. In view of this point, an object of the present invention is to provide a first-in, first-out storage device that can store data in a storage area of n words or less when storing n consecutive words of the same data. Means for Solving the Problems The present invention GEL A storage element having two ports for writing and reading and consisting of a plurality of words having a data field section for storing data and a word number field section for storing the number of pieces of data. a write pointer that indicates a write address; a read pointer that indicates a read address; a first latch that temporarily holds input data; a comparator that compares input data with data in the first latch; a first counter that is counted by a match detection signal generated when the input data from the first latch matches the first latch; and a second latch that holds the data read from the data field section of the storage element. and a second counter whose initial value is set to the value read from the word number field of the storage element, the write pointer being controlled by the comparator, and the read pointer being controlled by the second counter. The present invention is also applicable to a first-in, first-out storage device characterized in that, with the above-described configuration, for n consecutive words of the same data, the data l word and the number of words n are
can be stored, and when reading the data, it is possible to read n words of data depending on the number of words n. Therefore, when the same continuous data is written, the storage area is saved. Embodiment 1 FIG. 1 shows a configuration diagram of a first-in first-out storage device according to an embodiment of the present invention. 4 20 has a write port and a read port; a data field section for storing data; and a data field section for storing data; It is a two-port storage element consisting of a field for the number of words to be stored.A address for writing and reading data is specified independently by write pointer 2 and read pointer 3.4 indicates the latest data to be written. This is a first latch that is temporarily held, and the data of this first latch 4 and the data input from the outside are connected to a comparator 5.
When the match detection signal is input to the first counter 6, a match detection signal is output (if the match detection signal is input to the first counter 6).
counts the number of consecutive matches.The match detection signal passed through the inverter 7 is input as the control input of the write pointer 2 and the first latch 4.
According to the address specified by the read pointer 3, the data to be read next is copied from the data field section of the storage element 20 to the second latch 8 and from the word number field section to the second counter 9, respectively. The second counter 9 is decremented by the read request signal CLK, and when the count value reaches O, an O detection signal is input to the read pointer 3 and the second latch 8.

The second latch 8 holds the data until the 0 detection signal is applied, and outputs the data to the outside in response to the request signal CLK. Diagram This is a schematic diagram showing the operation in the configuration shown in Figure 1, and there are three steps.
In the initial state, when no data is stored in the storage element 20, write pointer 2 and read pointer 3 specify the same address, but after several words of data have been written (above), write pointer 2 moves from read pointer 3 to In step 1 shown in Fig. 3 (a), (friend B, B, B,
This shows the state after 6 words of data of C have been written in this order. Even if the address where written data A is stored is specified, the first latch 4 holds the latest data C, and the first counter 6 holds the count value 1 of the latest data C. too
Even worse, the second latch 8 holds the data A to be read next, and the second counter 9 holds the number of words of data A, which is 2, as shown in FIG. 3(b). When ill data is read in step 2, A is read out, and data A is still held in the second latch 8, and even though the 20th counter 9 is decremented and holds 1, when data C is further written, data A remains in the second latch 8. The latch 4 of 1 is a force that does not change (the first counter 6 is incremented and holds 2, but at this time neither the write pointer 2 nor the read pointer 3 changes) (~ Subsequently, in step 3 shown in FIG. 3(C) (Friend) When data is read out, A is read out, and data B to be read out next is held in the second latch 8, and the second counter 9
holds the number of words of data B, 3, and further data D
When , data C, which is different from the data C held in the first latch 4, and its word count 2 are written to the storage element 20 at the address specified by the write pointer 2, and the data C is written to the first latch 4. Although the latest data D is stored and l is set in the first counter 6, both the write pointer 2 and the read pointer 3 are incremented. As described above, it is possible to provide a first-in-first-out storage device that requires a storage area of n words or less when data is written continuously. It is possible to realize a first-in, first-out storage device that operates normally with a storage capacity of fewer words than the actual data, and its practical effect is large I,%.

[Brief explanation of drawings]

FIG. 1 shows the configuration of a first-in first-out storage device according to an embodiment of the present invention. FIG. 2 shows the configuration of a conventional first-in first-out storage device. FIG. 3 is a schematic diagram illustrating the operation of a first-in first-out storage device according to an embodiment of the present invention. Aml, 20...Memory element 2...Writing point Kyu
3... Readout point 4... First latch,
5... Combare Hisa 6... First Karan Hisa 8.
...Second latch, 9...Second counter.

Claims (1)

[Claims] a storage element having two ports for writing and reading, and comprising a plurality of words having a data field section for storing data and a word number field section for storing the number of pieces of data; a write pointer indicating a write address; a read pointer indicating a read address; a first latch that temporarily holds input data; a comparator that compares the input data with data in the first latch; a first counter that is counted by a match detection signal generated when the latches match, a second latch that holds data read out from the data field section of the storage element, and a word count field section of the storage element. a second counter in which the read value is set as an initial value, the write pointer being controlled by the comparator, and the read pointer being controlled by the second counter. .