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SN74ALVC3651 Datasheet(PDF) 8 Page - Texas Instruments |
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SN74ALVC3651 Datasheet(HTML) 8 Page - Texas Instruments |
8 / 26 page SN74ALVC3651 2048 × 36 SYNCHRONOUS FIRST-IN, FIRST-OUT MEMORY SDMS025A – OCTOBER 1999 – REVISED DECEMBER 1999 8 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 Table 3. Port-B Enable Function Table CSB W/RB ENB MBB CLKB B0–B35 OUTPUTS PORT FUNCTION H X X X X In high-impedance state None L L L X X In high-impedance state None L L H L ↑ In high-impedance state None L L H H ↑ In high-impedance state Mail2 write L H L L X Active, FIFO output register None L H H L ↑ Active, FIFO output register FIFO read L H L H X Active, mail1 register None L H H H ↑ Active, mail1 register Mail1 read (set MBF1 high) The setup- and hold-time constraints to the port clocks for the port-chip selects and write/read selects are only for enabling write and read operations and are not related to high-impedance control of the data outputs. If a port enable is low during a clock cycle, the port-chip select and write/read select can change states during the setup- and hold-time window of the cycle. When OR is low, the next data word is sent to the FIFO output register automatically by the CLKB low-to-high transition that sets OR high. When OR is high, an available data word is clocked to the FIFO output register only when a FIFO read is selected by CSB, W/RB, ENB, and MBB. synchronized FIFO flags Each FIFO flag is synchronized to its port clock through at least two flip-flop stages. This is done to improve the flag’s reliability by reducing the probability of metastable events on their outputs when CLKA and CLKB operate asynchronously with one another. OR and AE are synchronized to CLKB. IR and AF are synchronized to CLKA. Table 4 shows the relationship of each flag to the number of words stored in memory. Table 4. FIFO Flag Operation NUMBER OF WORDS IN FIFO†‡ SYNCHRONIZED TO CLKB SYNCHRONIZED TO CLKA IN FIFO†‡ OR AE AF IR 0 L L H H 1 to X H L H H (X + 1) to [2048 – (Y + 1)] H H H H (2048 – Y) to 2047 H H L H 2048 H H L L † X is the almost-empty offset for AE. Y is the almost-full offset for AF. ‡ When a word is present in the FIFO output register, its previous memory location is free. |
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