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LF2250 Arkusz danych(PDF) 2 Page - LOGIC Devices Incorporated |
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LF2250 Arkusz danych(HTML) 2 Page - LOGIC Devices Incorporated |
2 / 15 page DEVICES INCORPORATED LF2250 12 x 10-bit Matrix Multiplier Video Imaging Products 08/16/2000–LDS.2250-L 2 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 enabled registers. All timing specifi- cations are referenced to the rising edge of CLK. Inputs A11-0, B11-0, C11-0 — Data Inputs A, B, and C are the 12-bit registered data input ports. Data presented to these ports is latched into the multi- plier input registers for the current operating mode (Table 1). In the filter modes (Modes 01, 10, 11), the rising edge of CLK internally right-shifts new data to the next filter tap. KA9-0, KB9-0, KC9-0 — Coefficient Inputs KA, KB, and KC are the 10-bit regis- tered coefficient input ports. Data presented to these ports is latched into the corresponding internal coefficient register set defined by CWE1-0 (Table 4) on the next rising edge of CLK. Table 3 shows which coefficient registers are available for each coefficient input port. MODE1-0 OPERATING MODE 00 3 x 3 Matrix Multiplier 01 9-Tap FIR Filter 10 3 x 3 Convolver 11 4 x 2 Convolver TABLE 1. MODE SELECTION BIT WEIGHTING The internal sum of products of the LF2250 can grow to 23 bits. However, in order to keep the output format of the matrix multiply mode (Mode 00) identical to the input format, the X, Y, and Z outputs are truncated to 12-bit integer words. In the filter modes (Modes 01, 10, 11), the cascade output is always half-LSB rounded to 16 bits (12 integer bits and 4 fractional bits). The user may half-LSB round the output to any size less than 16 bits by simply forcing a “1” into the bit position of the cascade input immedi- ately below the desired LSB. For example, if half-LSB rounding to 12 bits is desired, then a “1” must be forced into the CASIN3 bit position (CASOUT4 would then be the LSB). In all four modes, the user may adjust the bit weighting, by applying an identical scaling correction factor to both the input and output data streams. If the coefficients are re- scaled, then the relative weightings of the cascade-in and cascade-out ports will differ accordingly. Figure 1 illustrates the input and output bit weightings for all four modes. DATA OVERFLOW Because the LF2250’s matched input and output data formats accommodate unity gain (0 dB), input conditions that could lead to numeric overflow may exist. To ensure that no overflow conditions occur, the user must be aware of the maximum input data and coefficient word sizes allowable for each specific algorithm being per- formed. OPERATING MODES The LF2250 can realize four different user-selectable digital filtering architec- tures as determined by the state of the mode (MODE1-0) inputs. Upon selection of the desired function, the LF2250 automatically chooses the appropriate internal data paths and input/output bus structure. Table 1 details the modes of operation. DATA FORMATTING The coefficient input ports (KA, KB, KC) are 10-bit fractional two’s comple- ment format regardless of the operating mode. The data input ports (A, B, C) are 12-bit integer two’s complement format regardless of the operating mode. In the matrix multiplier mode (Mode 00), the data output ports (X, Y, Z) are 12-bit integer two’s complement format. In the FIR filter and convolver modes (Modes 01, 10, 11), the X, Y, and Z ports are configured as the cascade-in (CASIN15-0) and cascade-out (CASOUT15-0) ports. These ports assume 16-bit (12-bit integer, 4-bit fractional) two’s complement data on both the inputs and outputs. Table 2 shows the data port formatting for each of the four operating modes. TABLE 2. DATA PORT FORMATTING PIN NAMES MODE1-0 A11-0 B11-0 C11-0 KA9-0 KB9-0 KC9-0 XC11-0 YC11-8 Y7-4 YC3-0 ZC11-0 00 A11-0 B11-0 C11-0 KA9-0 KB9-0 KC9-0 X11-0 Y11-8 Y7-4 Y3-0 Z11-0 01 A11-0 A11-0 NC KA9-0 KB9-0 KC9-0 CASIN15-4 CASIN3-0 NC CASOUT3-0 CASOUT15-4 10 A11-0 B11-0 C11-0 KA9-0 KB9-0 KC9-0 CASIN15-4 CASIN3-0 NC CASOUT3-0 CASOUT15-4 11 A11-0 B11-0 NC KA9-0 KB9-0 KC9-0 CASIN15-4 CASIN3-0 NC CASOUT3-0 CASOUT15-4 |
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