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PDSP16116 Datasheet(PDF) 8 Page - Mitel Networks Corporation |
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PDSP16116 Datasheet(HTML) 8 Page - Mitel Networks Corporation |
8 / 17 page PDSP16116 8 MBFP Mode select. When high, block floating point (BFP) mode is selected. This allows the device to maintain the dynamic range of the data using a series of word tags. This is especially useful in FFT applications. When low, the chip operates in normal mode for more general applications. This pin is intended to be tied high or low, depending on application. WTOUT1:0 (BFP Mode Only) Word tag output. This tag records the weighting of the output words from the current cycle relative to the current global weighting register (see Table 6). It should be stored along with the A ′ and B′ words as it will form the input word tags, WTA and WTB, for each complex word during the next pass. In normal mode, WTOUT1:0 are not used and should be left unconnected. Weighting of the output relative to the current global weighting register WTOUT1:0 One less The same One more Two more 00 01 10 11 Table 6 Word tag weightings Function WTB1:0 Shift complex product 1 place to the left No shift applied Shift complex product 1 place to the right Shift complex product 2 places to the right 11 00 01 10 Table 7 Normal mode shift control SFTA1:0 (BFP and Normal Modes) In BFP mode, these signals act as the A-word shift control. They allow shifting from one to four places to the right, (see Table 8). Depending on the relative weightings of the A-words and the complex product, the A-word may have to be shifted to the right to ensure compatible weightings at the inputs to the PDSP16318 complex accumulator. The two words must have the same weighting if they are to be added. In normal mode, SFTA0 performs a different function. If WTB1:0 is set to implement a left shift, then overflow will occur if the data is fully 32 bits wide. This pin is used to flag such an overflow. SFTA1 is not used in normal mode. Function SFTA1:0 Shift A-word 1 place to the right Shift A-word 2 places to the right Shift A-word 3 places to the right Shift A-word 4 places to the right 00 01 10 11 WTA1:0 (BFP Mode Only) Word tag from the A-word. This word records the weighting of the A-word relative to the global weighting register on the previous pass. Although the A-word itself is not processed in the PDSPl 6116, this information is required by the control logic for the radix 2 butterfly FFT application. These inputs should be tied low in normal mode. WTB1:0 (BFP and Normal Modes) In BFP mode, this is the word tag from the B-word. This is operated in the same manner as WTA but for the B-word. The value of the word tags are used to ensure that the binary weight- ing of the A-word and the product of the complex multiplier are the same at the inputs to the complex accumulator. Depending on which word is the larger, the weighting adjustment is per- formed using either the internal shifter or an external shifter con- trolled by SFTA. The word tags are also used to maintain the weighting of the final result to within plus two and minus one binary points relative to the new GWR. (On the first pass all word tags will be ignored). In normal mode. these inputs per- form a different function. They directly control the internal shifter at the output port as shown in Table 7. Table 8 External A-word shift control GWR4:0 (BFP Mode Only) Contents of the global weighting register. The GWR stores the weighting of the largest word present with respect to the weighting of the original input words. Hence, if the contents of the GWR are 00010, it indicates that the largest word currently being processed has its binary point two bits to the right of the original data at the start of the BFP calculations. The contents of this register are updated at the end of each pass, according to the largest value of WTOUT occuring during that pass. For example, if WTOUT = 11, then GWR will be increased by 2 (see Table 6). The GWR is presented in two’s complement format. In normal mode, GWR4:0 are not used and should be left unconnected. Start of BFP. This input should be held low for the first cycle of the first pass of the BFP calculations (see Fig.7). It serves to reset the internal registers associated with BFP control. When operating in normal mode this input should be tied low. End of pass. This input should be held low for the last cycle of each pass and for the lay time between passes. It instructs the control logic to update the value of the global weighting reg- ister and prepare the BFP circuitry for the next pass. When op- erating in normal mode this input should be tied low. AR15:13 (BFP Mode Only) Three MSBs of the real part of the A-word. These are used in the FFT butterfly application (see Fig. 4) to determine the magnitude of the real part of the A-word and, hence, to deter- mine if there will be any change of word growth in the PDSP16318 Complex Accumulator. When operating in normal mode, these inputs are not used and may be tied low. AI15:13 (BFP Mode Only) Three MSBs of the imaginary part of the A-word. Used in the same fashion as AR15:13. SFTR2:0 (BFP Mode Only) Accumulator result shift control. These pins should be linked directly to the S2:0 pins on the PDSP16318 Complex Accumulator. They control the accumulator’s barrel shifter (see Table 5). The purpose of this shift is to minimise sign extension in the multiplier or accumulator ALUs. In normal mode, SFTR2:0 are not used and should be left unconnected. Table 5 Accumulator shifts (BFP mode) SFTR2:0 000 001 010 011 100 101 110 111 Reserved Reserved Reserved Shift right by one No shift Shift left by one Shift left by two Reserved Function SOBFP (BFP Mode Only) EOPSS (BFP Mode Only) |
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