[sdiy] Digital delay memory

[Scott Gravenhorst]

Regarding SPI, one of the Microchip devices mentioned (1024 kbits) 
supports the 4 line SQI format, so their transfer speed is significantly 
faster than plain SPI.  Does require 3 more pins.

The thing that disappoints me is that the dsPIC33F is too old to have 
SQI built in.  Dunno about dsPIC33E, but that doesn't have the 16 bit 
DACs.  The DMA devices are quite powerful in the dsPIC and operate in 
parallel with the CPU which would make the quad interface nice.  I use 
SPI DMA with those devices on a dsPIC, but it's fast enough to do only 
delay really.  One can also use 2 RAM chips and 2 SPI channels for a bit 
more throughput as well as double the RAM size.

-- ScottG