User Manual

AND8399/D
http://onsemi.com
22
Timer Overflow ?
Power Up
Initialize microcontroller
Set Coil Current
Set Stepping Mode
Enable Motor
Send NXT Pulse
Start Timer
Y
N
If MSP =
(4 OR 36 OR 68
Y
N
Delay
Sample SLA−pin
Read Microstep
Position
Values only valid for 1/8 micro−stepping
See Table 1 for other stepping modes
Status Register 3
Figure 23. Sample SLA voltage (1/8 microstepping)
or 100)
The disadvantage of above flowchart is the need to read
out the Microstep Position. Because this takes time (SPI
communication), this will limit the maximum operating
speed. If needed the microcontroller could implement his
own positioner to keep track. This would eliminate the
needed SPI communication. This is however out of the
scope of this document.
Above flowchart can be used when transparency mode is
set to Not Transparent or Transparent. However, if
Transparent is used the delay before sampling of the
SLA−pin can be removed.
If Transparent mode is chosen, the SLA−pin could already
be sampled during the coil current zero crossing. This is
given in Figure 24.
When the coil current zero crossing is entered, the
SLA−pin will be sampled. A delay is added before sampling.
In this case this delay is needed to make sure the clamping
and transient phase are ended and the real BEMF is sampled
(see also Figures 11 and 21).