Motor Drivers

If the voltage of the Vref pin is made variable between 0 V and 5 V, how is the motor speed controlled??
(For example, does the output duty change?)

If the Vs voltage is fixed, the current that flows in the coil is also constant, so the number of rotations is also constant.
By configuring a clamping circuit using the external diode of the Vref pin, the loss of the external higher- side transistors can be kept constant and independent of Vs.

Refer to page 8 of the technical document (Japanese).
When Vref is made 0 V, the base voltage of the external upper transistor becomes -VBE, so the upper transistor is switched off.
The same applies even when Vref is less than 3 VBE.

For details, refer to Figure 1 on page 3 of the Application Notes (Japanese).

If pulse output is performed, such as 1000 continuous steps, independently of the VD cycle, how should the register be set?

In the case of the uPD16835, the possible setting pulse is maximum 252 during 1 VD cycle (FF2: During 1 cycle of origin wait + origin excitation wait).
Note, however, that the number of output pulses should be set in 4 pulse steps. Thus 1000 continuous pulses cannot be output during 1 VD cycle.

If pulse output is performed, such as 1000 continuous steps, independently of the VD cycle, how should the register be set?

In the case of the uPD16879, the output pulse count during 1 VD cycle is 1020 pulses maximum. Therefore, by making the settings of the 6th byte (α:motor pulse count setting) and 10th byte (β:motor pulse count setting) to (D7 to D0) = (11111010), 1000-pulse output during 1 VD cycle is possible.