Reading through the manual... the arb capability is crippled (DDS with arb alongside) and these units lack flexibility. Arbs only free-run (for either infinite or for N cycles_), and there is no way to trigger single arb bursts, externally or internally. Which means, for instance, you can't use the pulse gen to generate timed arb bursts. And there is no Sync Out signal in arb mode! Burst functions and external triggering only work on the DDS-generated waveforms.