During power on initialization or after RESET- is negated, DASP- shall be
asserted by Drive 1 within 400 msec to indicate that Drive 1 is present.
Drive 0 shall allow up to 450 msec for Drive 1 to assert DASP-. If Drive 1
is not present, Drive 0 may assert DASP- to drive an activity LED.
There are a few other sections like 6.3.13 (power-on diagnostics) and 6.3.16 (optional spindle sync) where it's pretty clear that Drive 1 follows Drive 0's lead.
There are times when the slave drive communicates with the master (rather than the host controller), and the master controls things.
I'm the opposite of an expert, but here's one example according to a document (https://www.ele.uri.edu/courses/ele408/s2001/projects/roland...) that I found. From section 6.3.4:
There are a few other sections like 6.3.13 (power-on diagnostics) and 6.3.16 (optional spindle sync) where it's pretty clear that Drive 1 follows Drive 0's lead.