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SN74V245-7PAG Datasheet(PDF) 10 Page - Texas Instruments |
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SN74V245-7PAG Datasheet(HTML) 10 Page - Texas Instruments |
10 / 43 page SN74V215, SN74V225, SN74V235, SN74V245 512 × 18, 1024 × 18, 2048 × 18, 4096 × 18 DSP-SYNC FIRST-IN, FIRST-OUT MEMORIES SCAS636E – APRIL 2000 – REVISED SEPTEMBER 2002 10 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 functional description (continued) Table 3. Status Flags for FWFT Mode NUMBER OF WORDS IN FIFO IR PAF HF PAE OR SN74V215 SN74V225 SN74V235 SN74V245 IR PAF HF PAE OR 0 0 0 0 L H H L H 1 to (n+1)† 1 to (n+1)† 1 to (n+1)† 1 to (n+1)† L H H L L (n+2) to 257 (n+2) to 513 (n+2) to 1025 (n+2) to 2049 L H H H L 258 to [513–(m+1)]‡ 514 to [1025–(m+1)]‡ 1026 to [2049–(m+1)]‡ 2050 to [4097–(m+1)]‡ L H L H L (513–m) to 512 (1025–m) to 1024 (2049–m) to 2048 (4097–m) to 4096 L L L H L 513 1025 2049 4097 H L L H L † n = Empty offset (SN74V215 n = 63; SN74V225, SN74V235, and SN74V245 n = 127) ‡ m = Full offset (SN74V215 m = 63; SN74V225, SN74V235, and SN74V245 m = 127) STANDARD MODE In this mode, status flags FF, PAF, HF, PAE, and EF operate in the manner outlined in Table 4. To write data into the FIFO, write enable (WEN) must be low. Data presented to the data-in lines is clocked into the FIFO on subsequent transitions of the write clock (WCLK). After the first write is performed, the empty flag (EF) goes high. Subsequent writes continue to fill the FIFO. The programmable almost-empty flag (PAE) goes 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 4. This parameter also is user programmable. See the Programmable Flag Offset Loading section. If data continues to be written into the FIFO, and no read operations are taking place, the half-full flag (HF) switches to low when the 257th (SN74V215), 513th (SN74V225), 1025th (SN74V235), and 2049th (SN74V245) word, is written into the FIFO. Continuing to write data into the FIFO causes the programmable almost-full flag (PAF) to go low. Again, if no reads are performed, PAF goes low after (512 – m) writes for the SN74V215, (1024 – m) writes for the SN74V225, (2048 – m) writes for the SN74V235 and (4096 – m) writes for the SN74V245. Offset m is the full offset value. This parameter also is user programmable. See the Programmable Flag Offset Loading section. If there is no full offset specified, PAF is low when the device is 63 away from full for SN74V215, and 127 away from full for the SN74V225, SN74V235, and SN74V245. When the FIFO is full, the full flag (FF) goes low, inhibiting further write operations. If no reads are performed after a reset, FF goes low after D writes to the FIFO. D = 512 for the SN74V215, 1024 for the SN74V225, 2048 for the SN74V235, and 4096 for the SN74V245. If the FIFO is full, the first read operation causes FF to go high. Subsequent read operations cause PAF and the half-full flag (HF) to go high under the conditions described in Table 4. If further read operations occur, without write operations, the programmable almost-empty flag (PAE) goes low when there are n words in the FIFO, where n is the empty offset value. If there is no empty offset specified, PAE is low when the device is 63 away from completely empty for SN74V215, and 127 away from completely empty for SN74V225, SN74V235, and SN74V245. Continuing read operations cause the FIFO to be empty. When the last word has been read from the FIFO, EF goes low, inhibiting further read operations. REN is ignored when the FIFO is empty. |
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