What pulse control actually does
A pulse output is a train of steps: the controller decides the position, the drive counts the steps. The R8 accepts 500 kpps differentially or 200 kpps single-ended, in direction-plus-pulse, CW/CCW or A/B quadrature form, with an electronic gear ratio from 1 to 1,073,741,824.
It is simple, deterministic and cheap. It is also open loop from the controller's point of view: the controller knows how many steps it sent, not where the axis is, unless the drive reports back over a separate link.
What changes with EtherCAT
The bus moves the position loop into the drive and sends a setpoint every cycle. On the R8 that means 2×100 Mbps full duplex, 100 axes at 0.1 ms of transmission delay, a 1 ms synchronisation cycle as standard and integer multiples of 250 µs below that, with CSP, CSV and CST modes.
The practical consequences are three: axes share a clock, the controller can read actual position every cycle, and the cable count drops to one per drive in a daisy chain instead of a pulse pair plus a direction pair plus an enable.
The crossover, honestly
Four axes on a machine with no interpolation between them: pulse is cheaper, and the wiring is not a problem. Electronic cam between two axes on a packaging machine: pulse can do it in the controller, and many machines run that way for years.
The crossover arrives at the point where the controller has to correct one axis based on another within the same cycle — registration control at speed, coordinated contouring, gantry levelling, or more than eight axes. Below that, pulse is often the rational choice and the money is better spent on encoders.
Retrofit arithmetic
A retrofit usually has motors already on the machine. If those motors take pulse command, the R8 P-variant is a drop-in and the new controller can drive them without touching the mechanics. If they take EtherCAT, the Z-variant is the match. Changing command type means changing drives, which means opening the cabinet, which means the retrofit budget just doubled.
This is why the R8 range keeps both: the same motor, the same cables, the same footprint, two command interfaces. The decision can be deferred to the point where the machine's axis count is known.