Sat May 17 23:20:33 EDT 2014

Siggen with USB?

I'd like to build a signal generator based on MCP4922 SPI DAC.  Max
SPI on 48MHz is 12MHz.  Chip needs 2 bytes/sample.  Max rate is about
600kHz.  With PIC running USB this needs to run from a timer
interrupt.  Problem is saving/restoring context if PIC is also running
USB interrupt.

Probably this is best done on a chip with DMA which can apparently[1]
be found on 18F46J11[2] ("Looking closer I see it on few newer
18FxxJxx devices like: 18FxxJ13, 18FxxJ50, 18FxxJ53")

Data sheet lists it as "1024-byte SPI Direct Memory Access (DMA)".

I think I have some newer 18F46K22 in the box, they don't have it.

[1] http://www.microchip.com/forums/m534827.aspx
[2] http://ww1.microchip.com/downloads/en/DeviceDoc/39932D.pdf