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IDT72285L20TF Datasheet(PDF) 7 Page - Integrated Device Technology |
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IDT72285L20TF Datasheet(HTML) 7 Page - Integrated Device Technology |
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7 / 25 page  7 COMMERCIAL TEMPERATURE RANGE IDT72275/72285 SUPERSYNC FIFO™ 32,768 x 18, 65,536 x 18 D = 32,768 writes for the IDT72275 and 65,536 for the IDT72285, respectively. If the FIFO is full, the first read operation will cause FF to go HIGH. Subsequent read operations will cause PAF and HF to go HIGH at the conditions described in Table 1. If further read operations occur, without write operations, PAE will go LOW when there are n words in the FIFO, where n is the empty offset value. Continuing read operations will cause the FIFO to become empty. When the last word has been read from the FIFO, the EF will go LOW inhibiting further read operations. REN is ignored when the FIFO is empty. When configured in IDT Standard mode, the EF and FF outputs are double register-buffered outputs. Relevant timing diagrams for IDT Standard mode can be found in Figure 7, 8 and 11. FIRST WORD FALL THROUGH MODE (FWFT) In this mode, the status flags, IR, PAF, HF, PAE, and OR operate in the manner outlined in Table 2. To write data into to the FIFO, WEN must be LOW. Data presented to the DATA IN lines will be clocked into the FIFO on subsequent transi- tions of WCLK. After the first write is performed, the Output Ready ( OR) flag will go LOW. Subsequent writes will continue to fill up the FIFO. PAE will go HIGH after n + 2 words have been loaded into the FIFO, where n is the empty offset value. The default setting for this value is stated in the footnote of Table 2. This parameter is also user programmable. See section on Programmable Flag Offset Loading. If one continued to write data into the FIFO, and we assumed no read operations were taking place, the HF would toggle to LOW once the 16,386th word for the IDT72275 and 32,770th word for the IDT72285, respectively was written into the FIFO. Continuing to write data into the FIFO will cause the PAF to go LOW. Again, if no reads are performed, the PAF will go LOW after (32,769-m) writes for the IDT72275 and (65,537-m) writes for the IDT72285, where m is the full offset value. The default setting for this value is stated in the footnote of Table 2. When the FIFO is full, the Input Ready ( IR) flag will go HIGH, inhibiting further write operations. If no reads are performed after a reset, IR will go HIGH after D writes to the FIFO. D = 32,769 writes for the IDT72275 and 65,537 writes for the IDT72285, respectively. Note that the additional word in FWFT mode is due to the capacity of the memory plus output register. If the FIFO is full, the first read operation will cause the IR flag to go LOW. Subsequent read operations will cause the PAF and HF to go HIGH at the conditions described in Table 2. If further read operations occur, without write operations, the PAE will go LOW when there are n + 1 words in the FIFO, where n is the empty offset value. Continuing read operations will cause the FIFO to become empty. When the last word has been read from the FIFO, OR will go HIGH inhibiting further read operations. REN is ignored when the FIFO is empty. When configured in FWFT mode, the OR flag output is triple register-buffered, and the IR flag output is double register- buffered. Relevant timing diagrams for FWFT mode can be found in Figure 9, 10 and 12. FUNCTIONAL DESCRIPTION TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH (FWFT) MODE The IDT72275/72285 support two different timing modes of operation: IDT Standard mode or First Word Fall Through (FWFT) mode. The selection of which mode will operate is determined during Master Reset, by the state of the FWFT/ SI input. If, at the time of Master Reset, FWFT/SI is LOW, then IDT Standard mode will be selected. This mode uses the Empty Flag ( EF) to indicate whether or not there are any words present in the FIFO. It also uses the Full Flag function ( FF) to indicate whether or not the FIFO has any free space for writing. In IDT Standard mode, every word read from the FIFO, including the first, must be requested using the Read Enable ( REN) and RCLK. If, at the time of Master Reset, FWFT/SI is HIGH, then FWFT mode will be selected. This mode uses Output Ready ( OR) to indicate whether or not there is valid data at the data outputs (Qn). It also uses Input Ready ( IR) to indicate whether or not the FIFO has any free space for writing. In the FWFT mode, the first word written to an empty FIFO goes directly to Qn after three RCLK rising edges, REN = LOW is not neces- sary. Subsequent words must be accessed using the Read Enable ( REN) and RCLK. Various signals, both input and output signals operate differently depending on which timing mode is in effect. IDT STANDARD MODE In this mode, the status flags, FF, PAF, HF, PAE, and EF operate in the manner outlined in Table 1. To write data into to the FIFO, Write Enable ( WEN) must be LOW. Data presented to the DATA IN lines will be clocked into the FIFO on subsequent transitions of the Write Clock (WCLK). After the first write is performed, the Empty Flag ( EF) will go HIGH. Subsequent writes will continue to fill up the FIFO. The Programmable Almost-Empty flag ( PAE) will go HIGH after n + 1 words have been loaded into the FIFO, where n is the empty offset value. The default setting for this value is stated in the footnote of Table 1. This parameter is also user programmable. See section on Programmable Flag Offset Loading. If one continued to write data into the FIFO, and we assumed no read operations were taking place, the Half-Full flag ( HF) would toggle to LOW once the 16,385th word for IDT72275 and 32,769th word for IDT72285 respectively was written into the FIFO. Continuing to write data into the FIFO will cause the Programmable Almost-Full flag ( PAF) to go LOW. Again, if no reads are performed, the PAF will go LOW after (32,768-m) writes for the IDT72275 and (65,536-m) writes for the IDT72285. The offset “m” is the full offset value. The default setting for this value is stated in the footnote of Table 1. This parameter is also user programmable. See section on Programmable Flag Offset Loading. When the FIFO is full, the Full Flag ( FF) will go LOW, inhibiting further write operations. If no reads are performed after a reset, FF will go LOW after D writes to the FIFO. |
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