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PDSP16510AC0AC Datasheet(PDF) 6 Page - Zarlink Semiconductor Inc |
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PDSP16510AC0AC Datasheet(HTML) 6 Page - Zarlink Semiconductor Inc |
6 / 23 page PDSP16510A 6 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 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 PDSP16510 always expects to receive 1024 words, regardless of the amount of block over- lapping. Data stored internally cannot be re-used when block overlapping is required, and data from the external buffer must be re-read as necessary. Fig. 6 illustrates a typical 1024 point system with an input buffer which supports complex input data. The input buffer can be provided by a PDSP16540 Bucket Buffer without the need for any external control logic. It supplies RAM for 1024 x 32 complex words, and allows transfers to the FFT Proces- sor at the full system clock rate. The PDSP16540 also sup- ports the standard 50% and 75% data block overlapping, but in addition allows the user to define the amount of overlap to Table 1. Advanced Timing Information with Continuous Inputs. 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 10 ns Delay to LFLG going in-active ( 30 pf load ) T FL 10 ns Min time to INEN low in edge mode T ED 15 ns 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 within 32 words. 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 is defined below where Ø is in MHz and L is the system clock low time in nanoseconds : S = FØ, where F = 4 / (6+0.001ØL) F is typically 0.66 and applies to all transforms except for those of 1024 points, even if INEN is driven such that concurrent operations do not actually occur (Note also that S must be 16510A,A0,B0,C0 |
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