FIFO with almost full/almost empty flag

An almost full flag for a FIFO, comprising:

• a Read pointer for determining the location in the FIFO for reading information therefrom and for being incremented for each Read operation in response to receiving an external Read signal;
• a Write pointer for determining the location in the FIFO for writing information thereto and for being incremented for each Write operation in response to receiving an external Write signal;
• a first counter for being incremented in response to receipt of said external Read signal and having a first count value corresponding to the value of said Read pointer;
• a second counter for being incremented in response to receipt of said external Write signal and having a second count value corresponding to the value of said Write pointer such that the difference in the value of said first and second count values corresponds to the proximity of said Read and Write pointers;
• a compare circuit for comparing said first value with the second value and outputting a compare signal state when said first and second count values have a predetermined difference therebetween, said compare signal represented by a first logic state and the output of said compare means being at a second logic state when said compare signal is not generated;
• set means for generating a set signal in response to the presence of said compare signal when said external Write signal is received;
• reset means for generating a reset signal in response to the presence of said compare signal;
• blanking means for inhibiting generation of said reset signal by said reset means for a predetermined duration of time after receipt of said external Read signal to prevent said reset signal from being generated proximate to the output of said compare circuit making a transition from said first logic state to said second logic state;
• and
• a flag for being placed in a set position when said set signal is generated and for being placed in a reset position in response to generation of said reset signal.

A method for indicating an almost full condition for a FIFO, comprising:

• providing a Read pointer that determines the location of the FIFO for reading information therefrom, the Read pointer incremented for each Read operation in response to receiving an external Read signal;
• providing a Write pointer for determining the location in the FIFO for writing information thereto, the Write pointer being incremented for each Write operation in response to receiving an external Write signal;
• determining the difference between the Read and Write pointers and controlling a compare signal to make a change from a first logic state to a second logic state when the difference equals a predetermined proximity value and for changing from the second logic state to the first logic state when the proximity changes from the predetermined proximity value;
• generating a set signal in response to the compare signal being at the second logic state when the external Write signal is received;
• generating a reset signal in response to the compare signal being at the second logic state;
• inhibiting generation of the reset signal for a predetermined duration of time after receipt of the external Read signal to prevent the reset signal from being generated when the compare signal makes a transition from the first logic state to the second logic state;
• and
• placing a flag in a set position when the set signal is generated and replacing the flag in the reset position in response to generation of the reset signal.