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IDT723622 Datasheet(PDF) 10 Page - Integrated Device Technology |
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IDT723622 Datasheet(HTML) 10 Page - Integrated Device Technology |
10 / 26 page 5.22 10 IDT723622/723632/723642 CMOS SyncBiFIFO ™ 256 x 36 x 2, 512 x 36 x 2, 1024 x 36 x 2 COMMERCIAL TEMPERATURE RANGE FS1 FS0 RST1 RST1 RST2 RST2 X1 AND Y1 REGlSTERS(1) X2 AND Y2 REGlSTERS(2) HH ↑ X64 X HH X ↑ X64 HL ↑ X16 X HL X ↑ X16 LH ↑ X8 X LH X ↑ X8 LL ↑↑ Programmed from port A Programmed from port A NOTES: 1. X1 register holds the offset for AEB; Y1 register holds the offset for AFA. 2. X2 register holds the offset tor AEA; Y2 register holds the offset for AFB. Table 1. Flag Programming during the LOW-to-HIGH transition of its reset input. For example, to load the preset value of 64 into X1 and Y1, FS0 and FS1 must be HIGH when FlFO1 reset ( RST1) returns HIGH. Flag-offset registers associated with FIFO2 are loaded with one of the preset values in the same way with FIFO2 reset ( RST2). When using one of the preset values for the flag offsets, the FlFOs can be reset simultaneously or at different times. To program the X1, X2, Y1, and Y2 registers from port A, both FlFOs should be reset simultaneously with FS0 and FS1 LOW during the LOW-to-HIGH transition of the reset inputs. After this reset is complete, the first four writes to FIFO1 do not store data in RAM but load the offset registers in the order Y1, X1, Y2, X2. The port A data inputs used by the offset registers are (A7-A0), (A8-A0), or (A9-A0) for the IDT723622, IDT723632, or IDT723642, respectively. The highest num- bered input is used as the most significant bit of the binary number in each case. Valid programming values for the registers ranges from 1 to 252 for the IDT723622; 1 to 508 for the IDT723632; and 1 to 1020 for the IDT723642. After all the offset registers are programmed from port A, the port-B input- ready flag (IRB) is set HIGH, and both FIFOs begin normal operation. FIFO WRITE/READ OPERATION The state of the port-A data (A0-A35) outputs is controlled by port-A chip select ( CSA) and port-A write/read select (W/ RA). The A0-A35 outputs are in the High-impedance state when either CSA or W/RA is HIGH. The A0-A35 outputs are active when both CSA and W/RA are LOW. Data is loaded into FIFO1 from the A0-A35 inputs on a LOW-to-HIGH transition of CLKA when CSA is LOW, W/RA is HIGH, ENA is HIGH , MBA is LOW, and IRA is HIGH. Data is read from FIFO2 to the A0-A35 outputs by a LOW-to-HIGH transition of CLKA when CSA is LOW, W/RA is LOW, ENA is HIGH, MBA is LOW, and ORA is HIGH (see Table 2). FIFO reads and writes on port A are independent of any concurrent SIGNAL DESCRIPTION RESET The FIFO memories of the IDT723622/723632/723642 are reset separately by taking their reset ( RST1, RST2) inputs LOW for at least four port-A clock (CLKA) and four port-B clock (CLKB) LOW-to-HIGH transitions. The reset inputs can switch asynchronously to the clocks. A FIFO reset initializes the internal read and write pointers and forces the input-ready flag (IRA, IRB) LOW, the output-ready flag (ORA, ORB) LOW, the almost-empty flag ( AEA, AEB) LOW, and the almost-full flag ( AFA, AFB) HIGH. Resetting a FIFO also forces the mailbox flag ( MBF1, MBF2) of the parallel mailbox register HIGH. After a FlFO is reset, its input-ready flag is set HIGH after two clock cycles to begin normal operation. A FIFO must be reset after power up before data is written to its memory. A LOW-to HIGH transition on a FlFO reset ( RST1, RST2) input latches the value of the flag-select (FS0, FS1) inputs for choosing the almost-full and almost-empty offset program- ming method (see almost-empty and almost-full flag offset programming below). ALMOST-EMPTY FLAG AND ALMOST-FULL FLAG OFF- SET PROGRAMMING Four registers in the IDT723622/723632/723642 are used to hold the offset values for the almost-empty and almost-full flags. The port-B almost-empty flag ( AEB) offset register is labeled X1 and the port-A almost-empty flag ( AEA) offset register is labeled X2. The port-A almost-full flag ( AFA) offset register is labeled Y1 and the port-B almost-full flag ( AFB) offset register is labeled Y2. The index of each register name corresponds to its FIFO number. The offset registers can be loaded with preset values during the reset of a FIFO or they can be programmed from port A (see Table 1 ) . To load a FIFO almost-empty flag and almost-full flag offset registers with one of the three preset values listed in Table1, at least one of the flag-select inputs must be HIGH |
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