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PDSP16515AB0AC Datasheet(PDF) 7 Page - Zarlink Semiconductor Inc |
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PDSP16515AB0AC Datasheet(HTML) 7 Page - Zarlink Semiconductor Inc |
7 / 25 page PDSP16515A 7 The internal workspace is double buffered when 256 point transforms are to be performed. A separate output buffer is also provided. These resources, together with separate input and output buses, allow new data to be loaded and old results to be dumped, whilst the present transform is being computed. Additional, external, input buffering is not needed to prevent loss of incoming data whilst a transform is being performed. When block overlapping is required, internally stored data will be re-used, and a proportionally smaller number of new samples need be loaded. Note that the internal window operator still functions correctly since it is actually applied during the first pass, and not whilst data is being loaded. The internal RAM organisation is shown in Fig. 4. It should be noted that the amount of overlap between I/O transfers and transforms is completely under the control of the system, since an input enable signal (INEN) and an output enable (DEN) can be used to initiate transfers. In the 1024 point mode there is insufficient workspace for input and output buffering in addition to working memory. The device is then configured in a mode with separate load, transform and dump operations. The internal arrangement is shown in Fig. 5. The support of an external input buffer is needed if incoming samples are not to be lost whilst a Table 1. Advanced Timing Information with Continuous Inputs. TSD THD TSA THA 1 N/2 N TSI THI VALID TFH TFL 1 TFH 50% Overlap TFL N TSA TED DIS DATA IN INEN LFLG INEN Edge activated system Min Time =THA transform is in progress. This is loaded at the sample clock rate and transferred to the FFT processor as quickly as possible. In this mode the PDSP16515A always expects to receive 1024 words, regardless of the amount of block overlapping. Data stored internally cannot be re-used when block overlapping is required, and data from the external buffer must be re-read as necessary. If no incoming data is to remain un-processed, the user must ensure that the time taken to acquire sufficient data to instigate a new transform is greater than or equal to the transformation time itself. The latter can be calculated from Table 4, once the system clock rate has been defined. When 1024 point transforms are performed, both the time to read data from the input buffer, and also the time to dump data, must be included in the calculation to determine the minimum time in which data can be loaded into the external buffer. The peak transfer rate is limited by the characteristics of the I/ O circuits, but can be greater than the sampling rate which is determined by the transform time. When load and dump operations are not concurrent with transform operations ( as in the 1024 point modes ), then the maximum I/O rate is equal to the system clock rate, Ø. When other transform sizes are specified, the sampling rate, S, is reduced by a factor F. This Characteristic Symbol Min Max Units Data In set up Time T SD 10 ns Data In Hold Time T HD 0ns INEN active going set up T SA 8ns INEN active Hold Time T HA 0ns INEN in-active Hold Time to ensure no load T HI 2ns INEN in-active going set up for no load operation T SI 8ns Delay to LFLG going active ( 30 pf load ) T FH 18 ns Delay to LFLG going in-active ( 30 pf load ) T FL 18 ns Min time to INEN low in edge mode T ED 15 ns |
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