Data Sheet

AMIS−30543
http://onsemi.com
25
Figure 10. Translator Table: Circular and Square
I
Y
I
X
Start = 0
Step 1
Step 2
Step 3
1/4
th
micro step
I
Y
I
X
Start = 0
Step 1
Step 2
Step 3
Uncompensated
half step
I
Y
I
X
Start = 0
Step 1
Step 2
Compensated
half step
Step 3
I
Y
I
X
Start = 0
Step 1
Uncompensated
full step
Step 2
Step 3
I
Y
I
X
Start = 0
Step 1
Compensated full
step, 1 phase on
Step 2
Step 3
I
Y
I
X
Start = 0
Step 1
Compensated full
step, 2 phase on
Step 2
Step 3
Direction
The direction of rotation is selected by means of following
combination of the DIR input pin and the SPI−controlled
direction bit <DIRCTRL>. (see Table 12 SPI Control
Parameter Overview)
NXT Input
Changes on the NXT input will move the motor current
one step up/down in the translator table (even when the
motor is disabled: <MOTEN> = 0). Depending on the
NXT−polarity bit <NXTP> (see Table 12 SPI Control
Parameter Overview), the next step is initiated either on the
rising edge or the falling edge of the NXT input.
Translator Position
The translator position MSP[8:0] can be read in SPI Status
Register 3 and Status Register 4 (See Table 14 SR3 and
SR4). This is a 9−bit number equivalent to the 1/128
th
micro−step (see Table 9 “Circular Translator Table”). The
translator position is updated immediately following a NXT
trigger.
NXT
Update
Translator Position
Update
Translator Position
Figure 11. Translator Position Timing Diagram
Synchronization of Step Mode and NXT Input
When step mode is re−programmed to another resolution
(Figure 12), then this is put in effect immediately upon the
first arriving “NXT” input. If the micro−stepping resolution
is increased, the coil currents will be regulated to the nearest
micro−step, according to the fixed grid of the increased
resolution. If however the micro−stepping resolution is
decreased, then it is possible to introduce an offset (or phase
shift) in the micro−step translator table.
If the step resolution is decreased at a translator table
position that is shared both by the old and new resolution
setting, then the offset is zero and micro−stepping is
proceeds according to the translator table.
If the translator position is not
shared both by the old and
new resolution setting, then the micro−stepping proceeds
with an offset relative to the translator table (See Figure 12
right hand side).