JPH03241584A - Fifo memory - Google Patents

Abstract

PURPOSE:To accumulate new data in a memory without reading data by incrementing a write pointer and a read pointer by one and deleting data from old one when an overflow flag is raised. CONSTITUTION:The write pointer 2 is incremented by one and the number of write bytes is shown in a write byte counter 4 whenever a write pulse (d) is inputted to a FIFO memory 7 provided with the memory part 1 of n-bytes. It is the same as to the read pointer 3 and a read byte counter 5. When the difference of counted values between the counters 4 and 5 comes to a control variable, the pointer 2 to (n) and the control variable to (n), a read/write control part 6 raises the overflow flag (b). The control part 6 sets the pointer 2 to '0' adds the pointer 3 by one by a subsequent write operation pulse (d), and data are sequentially deleted from old one without reading old data and new data are accumulated in the memory part 1. Then, new data can always be received without being conscious of overflow.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a FIFO (first-in-first-out)
Regarding memory.

[Conventional technology]

Conventional FIFO memory has independent write pointers and read pointers, and when 1 byte is written, the write pointer is incremented by 1, and when 1 byte is read, the read pointer is incremented by 1. If the value of the read pointer becomes larger than the value of the write pointer, an empty flag is set. Furthermore, if the value of the write pointer becomes larger than the capacity (number of bytes) of the memory section, an overflow flag is set and writing to the memory section is prohibited. At this time, the data in the memory section is accumulated up to the time when the overflow flag is raised, and the write pointer is at the 0th byte. [Problem to be solved by the invention] In the conventional FIFO memory described above, overflow occurs. New data could not be loaded until the old data was read out.

[Means to solve the problem]

The FIFO memory of the present invention includes a read/write control unit using a write pointer, a read pointer, and an overflow flag, and in a write operation when the overflow flag is set, the write pointer is incremented by 1 and the read pointer is incremented by 1; Loads new data into memory without reading old data,
The configuration is such that the data already stored in the memory section is erased in the order of oldest data.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

Referring to FIG. 1 showing an embodiment of the present invention, 1 is n+
It is an internal memory section of the FIFO memory 7 and has a capacity of 1 byte. 2 is a write pointer, 3 is a read pointer, 4 is a write byte number counter, 5 is a read byte number counter, 6 is a read/write control unit, a is an empty flag, b is an overflow flag, C is a read pulse, d is a write pulse When there is no data in this FIFO memory 7, write pointer 2,
Both read pointers 3 are pointing to O.

When writing 1 byte, one write pulse d is input,
Light pointer 2 increases by +1. Also, light pulse d
The input number is represented by write byte number counter 4. Further, each time one byte is read, the read pointer 3 is also incremented by 1, and the value of the read byte number counter 5 is incremented by 1. The read/write control unit 6 has a value obtained by subtracting the value of the read byte number counter 5 from the value of the write byte number counter 4 as a control value. While the control value is smaller than n, the write pointer 2 is incremented by 1 and the write byte number counter 4 is incremented by 1 every time a write is performed.

If the control value indicates n when the value of write pointer 2 is n, an overflow flag b is set. In this next write operation, write pointer 2 is set to O and read pointer 3 is incremented by +1. The value of read byte number counter 5 does not change. If the read pulse C is input while the overflow flag b is set, the read pointer 3 is incremented by 1, and the read byte number counter 5 is also incremented by 1. At this time, the control value indicates n-1, so the overflow flag b
drop.

〔Effect of the invention〕

As explained above, according to the present invention, in a write operation when the overflow flag is set, the write pointer is incremented by 1, the read pointer is also incremented by 1, and data stored in the memory section is erased starting from the oldest data. New data can be loaded into the memory section. As a result, when used for data transmission, for example, new data can always be received, and there is no need for the data receiving side to have a circuit that is concerned with overflow of the memory section.

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Claims (1)

[Claims] A read/write control unit is provided with a write pointer, a read pointer, and an overflow flag, and when the overflow flag is set, the write operation increments the write pointer by 1 and the read pointer by 1, so that new data can be created without reading old data. A FIFO memory characterized in that data is loaded into a memory section and the data already loaded in the memory section is erased in the order of oldest data.