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LF43881 Datenblatt(PDF) 4 Page - LOGIC Devices Incorporated |
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LF43881 Datenblatt(HTML) 4 Page - LOGIC Devices Incorporated |
4 / 11 page DEVICES INCORPORATED LF43881 8 x 8-bit Digital Filter Video Imaging Products 08/16/2000–LDS.43881-J 4 OUTPUT STAGE DESCRIPTION The 26-bit adder contained in the output stage can add the contents of any filter cell accumulator (selected by ADR2-0) with the 18 most significant bits of the output buffer. The result is stored back into the output buffer. The complete operation takes only one clock cycle. The eight least significant bits of the output buffer are lost. The Zero multiplexer is controlled by the SHADD input signal. This allows selection of either the 18 most signifi- cant bits of the output buffer or all zeros for the adder input. When SHADD is LOW, all zeros will be selected. When SHADD is HIGH, the 18 most significant bits of the output buffer are selected enabling the shift- and-add operation. SHADD is latched and delayed internally by one clock cycle. The output multiplexer is also con- trolled by the SHADD input signal. This allows selection of either a filter cell accumulator, selected by ADR2-0, or the output buffer to be output to the SUM25-0 bus. Only the 26 least significant bits from either a filter cell accumulator or the output buffer are output on SUM25-0. If SHADD is LOW during two consecutive clock cycles (low during the current and previous clock cycle), the output multiplexer selects the contents of a filter cell accumulator addressed by ADR2-0. Otherwise, the output multiplexer selects the contents of the output buffer. If the same address remains on the ADR2-0 inputs for more than one clock cycle, SUM25-0 will not change to reflect any updates to the addressed cell accumulator. Only the result from the first selection of the cell (first clock cycle) will be output. This allows the interface of slow memory devices where the output needs to be active for more than one clock cycle. Normal FIR operation is not affected because ADR2-0 is changed sequentially. NUMBER SYSTEMS Data and coefficients can be repre- sented as either unsigned or two's complement numbers. The TCS and TCCI inputs determine which of the two formats is to be used. All values are represented as 9-bit two's comple- ment numbers internally. The value of the ninth bit is determined by the number system selected. The ninth bit is a sign extended bit when the two's complement mode is chosen. When the unsigned mode is chosen, the ninth bit is zero. SIGNAL DEFINITIONS Power VCC and GND +5 V power supply. All pins must be connected. Clock CLK — Master Clock The rising edge of CLK strobes all registers. All timing specifications are referenced to the rising edge of CLK. Inputs DIN7-0 — Data Input 8-bit data is latched into the X register of each filter cell simultaneously. The TCS signal selects the appropriate data format type. The DIENB signal enables loading of the data. CIN7-0 — Coefficient Input 8-bit coefficients are latched into the C register of Filter Cell 0. The TCCI signal selects the appropriate coeffi- cient format type. The CIENB signal enables loading of the coefficients. Outputs SUM25-0 — Data Output The 26-bit result from an individual filter cell will appear when ADR2-0 is used to select the filter cell result. SHADD in conjunction with ADR2-0 is used to select the output from the shift-and-add output stage. COUT7-0 — Coefficient Output The 8-bit coefficient output from Filter Cell 7 can be connected to the CIN7-0 coefficient input of the same LF43881 to recirculate the coefficients. COUT7-0 can also be connected to the CIN7-0 of another LF43881 to cascade the devices. The COENB signal enables the output of the coefficients. DCM1 DCM0 Decimation Function 0 0 Decimation registers not used 0 1 One decimation register used (decimation by one-half) 1 0 Two decimation registers used (decimation by one-third) 1 1 Three decimation registers used (decimation by one-fourth) TABLE 1. DECIMATION MODE SELECTION ERASE RESET Clearing Effect 0 0 All accumulators and all registers are cleared 0 1 Only the accumulator addressed by ADR2-0 is cleared 1 0 All registers are cleared (accumulators are not cleared) 1 1 No clearing occurs, internal state remains the same TABLE 2. REGISTER AND ACCUMULATOR CLEARING |
Ähnliche Teilenummer - LF43881 |
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Ähnliche Beschreibung - LF43881 |
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