22-09-2016, 06:26 PM
This sort of image can be re-used in any sort of memory, provided that it's accessed with the same clock rate as the original.
If I was designing something like this, I'd probably go for a significantly higher clock rate, at least 27MHz for 625. This simplifies the filter needed after the DAC while giving good frequency response. At 54MHz even a very accurate filter becomes trivial for a 6MHz bandwidth. But isn't this a waste of memory? Assuming the memory is fast enough (I think modern SD cards are amply fast) then at 54MHz each picture needs 54MHz/25Hz or just over 2Mbytes. Since 32GB SD cards are cheap and even bigger ones are readily available this is hardly a problem. Even if we allocate 4MB per frame to simplify addressing then a 32GB card would hold over 4000 frames or almost 3 minutes of moving pictures.
If I was designing something like this, I'd probably go for a significantly higher clock rate, at least 27MHz for 625. This simplifies the filter needed after the DAC while giving good frequency response. At 54MHz even a very accurate filter becomes trivial for a 6MHz bandwidth. But isn't this a waste of memory? Assuming the memory is fast enough (I think modern SD cards are amply fast) then at 54MHz each picture needs 54MHz/25Hz or just over 2Mbytes. Since 32GB SD cards are cheap and even bigger ones are readily available this is hardly a problem. Even if we allocate 4MB per frame to simplify addressing then a 32GB card would hold over 4000 frames or almost 3 minutes of moving pictures.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
