TM3 - Dual Channel Expanded

This is a time-base expansion mode like TM2 which supports dual channel operation like TM1.

In this case data capture is enabled for 2 PIC cycles every P PIC cycles where P is computed from the Time-base Expansion Register R13 according to:

P = 19 + 3 * (TB + 1)

P	expanded time-base period (in PIC cycles).
TB	8 bit time-base expansion (R13 -> 1 to 256, 0 read as 256).

The minimum time-base expansion period is 10.0 uS and the maximum 316 uS. This provides expanded time-base sample rates ranging from 3.165 kHz to 100 kHz. At all expanded time-base rates, 20 samples are acquired in a single burst at 25 MHz at each expanded time-base cycle.