Given out scaling and that n=300 on the secondary for the CT 0.1-P,
and a 16-bit DAC value, each LSB cancels out 900 µA of current on 
the primary, for a maximum range of
  DAC 0000h ≈ -29.5 A (-900 µA * 2^15)
  DAC 8000h ≈   0.0 A
  DAC ffffh ≈  29.5 A (900 µA * 2^15)

Let's use 14 bits from the DAC plus 4 bits from the CT to get 18 bits
total.  Analysis is over the positive range only for simplicity:

The range covered by a LSB on the DAC would be
  29.5A / 2^14 = 1.8 mA.
CT range should overlap slightly, so intend on measuring 2.5mA.
CT output is 5V at 100mA, so output is 125mV at 2.5mA.

To get 4 bits from that, we need to measure 7.8mV
PIC is measuring 12 bits over 2.5V which is 0.61mV.
So we only need to shift the CT output and limit it:

(PIC input) = clamp(0, 1.25V - (CT output), 2.5V)

Clamp by putting a 1K in series with diodes to VSS/VDD.

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Results are not promising.  The CT-0.1P does not want to behave
reasonably when the secondary is connected to the current source.
Earlier tests indicated it would, but now it's not... 
