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PDSP16515AA0GC Datasheet(PDF) 8 Page - Mitel Networks Corporation |
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PDSP16515AA0GC Datasheet(HTML) 8 Page - Mitel Networks Corporation |
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8 / 27 page  PDSP16515A 8 purpose. The edge is provided by INEN going low. Loading will cease when a complete block (or group of blocks with multiple concurrent transforms) of data has been loaded, even if INEN remains low. INEN must go high at some point after the minimum hold time has been satisfied, and then return low AFTER ALL DATA HAS BEEN LOADED, before a new load operation can commence. Low going edges which occur before all data has been loaded will be ignored. The INEN edge mode is actually provided for the correct operation of multiple device systems, but if Bit 12 in the Control Register is reset in the SINGLE device mode, the edge activated operation will still be possible. With all but 256 point complex transforms, the single device edge mode of operation is identical to that of a multiple device system. With 256 point transforms, and their concurrent derivatives, the location of the low going edge in the data stream is dependent on the amount of block overlapping. The low going edge transition must be provided after 64 samples have been loaded with 75% overlapping, and after 128 samples have been loaded with 50% overlapping. With no overlapping the edge must be provided after 256 samples have been loaded. In a single device system with Bit 12 set, INEN can be taken high to inhibit the load operation when gaps occur in the data stream. In the INEN edge activated mode gaps in the data stream can only be accommodated if the DIS clock is externally inhibited. Taking INEN high will not inhibit the loading of data in this mode. With gaps in the data stream the peak sampling rates can be higher than continuous sampling rates. When data loading is not coincident with transform operations the peak rate can equal that of the system clock, otherwise it is reduced by the factor, F, given on the opposite page. When Control Register Bit 12 is set in any multiple device mode, the DEF high going edge will also initiate a load operation after it has been internally synchronised to the rising DIS edge. If the first device in a multiple device system is programmed in this manner, the transform sequence will automatically start when DEF goes in-active. The other devices need the INEN edge as usual, and must have Bit 12 reset. A fuller explanation of the use of Bit 12 in a multiple device mode is given in the section on I/O In Multiple Device Systems. Note that the use of Bit 12 in a single device system ( Control Register Bits 10:9 = 00) is completely different to its use in a multiple device mode. The LFLG output goes active in response to the DIS rising edge used to load the first data sample, and indicates that a load operation is occurring. In an edge activated system the LFLG output will go high as the result of the first high going DIS edge after INEN has gone low. In the simple INEN enabling mode, internal logic counts the number of valid inputs and detects when the programmed block length has been reached. LFLG then goes low and will go high again in response to the next valid DIS strobe. LFLG will go low when DEF is active and will go high in response to the first INEN enabled DIS edge after DEF has gone in- active. 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 synchronous to SCLK). If this causes a system limitation in a single device application, then the device can be configured for pseudo, Mode 2, multiple device operation. Separate load, transform, and then dump operations will then always occur, but DEN must be low when a transform is complete or DAV will never go active. See the section on multiple device operation. Loading Data Data loading is controlled by three signals; DIS an input strobe, INEN a load enable, and LFLG an output flag. Detailed timing information is given in Table 1. Once sufficient data has been acquired, a transform will automatically commence. This is normally after a complete block has been loaded, except when a single device is performing overlapped transforms of 256 points or less. With 75% overlapping, transforms will commence after 25% of a new block has been loaded, and with 50% overlapping transforms commence after 50% of the data has been loaded. The remainder of the block is provided by data already stored in the internal RAM. The data strobe is used to load data into the internal workspace RAM, and data must meet the specified set up and hold times with respect to its rising edge. DIS can be a continuous input since the device only loads data when an input enabling signal is active. An internal synchronisation interval is necessary between the last sample being loaded with the DIS strobe and transforms being started with the system clock. This can be up to twelve system clock periods when data transfers and transforms are overlapped. The transform times given later in Table 4 are maximum values, and include these twelve periods. The way in which the INEN signal controls data loading is dependent on whether a single or multiple device is to be implemented, and the status of Control Register Bit 12. When Bit12 is set in a SINGLE device system the INEN signal is simply used as an enable for the DIS strobes. When INEN is low, and provided the relevant set up and hold times have been satisfied, data will be loaded with the rising edge of the DIS strobe. If no gaps occur within the incoming data, INEN can be tied permanently low, provided that the sampling rate has been chosen such that transforms are completed before a new block of data is loaded. For transforms of less than 1024 points, data will then be continually processed without any loss of information. In the 1024 point modes the device will cease loading data when 1024 samples have been loaded, and even if INEN remains low no more data will be accepted until the previous results have been dumped. In a multiple device system an edge is ALWAYS needed to commence a load operation, and Bit 12 has a different |
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