10.4.8.2 Using FIFO Flags

The AEVAL and AFVAL pins are used to specify the almost empty and almost full threshold values, respectively. They are 12-bit signals. In order to handle different read and write aspect ratios, the values specified by the AEVAL and AFVAL pins are to be interpreted as the address of the last word stored in the FIFO. The FIFO actually contains separate write address (WADDR) and read address (RADDR) counters. These counters calculate the 12-bit memory address that is a function of WW and RW, respectively. WADDR is incremented every time a write operation is performed and RADDR is incremented every time a read operation is performed. Whenever the difference between WADDR and RADDR is greater than or equal to AFVAL, the AFULL output is raised. Likewise, whenever the difference between WADDR and RADDR is less than or equal to AEVAL, the AEMPTY output is raised.