Product specifications
R01AN0168ED0101 Rev. 01.01 30
Application Note
Chapter 6 Performing Movements
6.1.1 Common 25-bit Number Format
For all parameters and variables which are 25 bits wide, a common number
format is given.
Figure 6-1 Common 25-bit Number Format
The number format consists of a sign flag, the macrosteps and the microsteps
values. The storage format is a binary fixed-point format, with bits [23:8] being
the integer and [7:0] the fraction part. Bit 24 is the sign (positive/negative),
which can be extended by software to 32 bits by copying bit 24. Negative
values are stored in 2’s complement.
(1) Sign Flag
All numbers within the Movement Calculator are signed numbers. This means,
that the position of
zero is a relative one. In fact, movements are always
calculated by relative distances. If by software the variable
VAP is set to a
certain value
p, before the Channel Management is started, this position now is
assumed to be the actual position. To move towards zero by more steps than
p, a negative value for the target position PMP would be entered.
Negative numbers have the sign flag set (1).
Note It makes sense to clear PMPn and VAPn after having reached the mechanical
zero point of an instrument (i.e., by
Zero Point Detection). Like this, all position
values would be positive, and other values would have a positive sign, if their
direction would point away from the mechanical stop, or have a negative sign,
if their direction would point towards the mechanical stop.
Table 6-2 Variables of the Movement Calculator
Variable
Abbreviation /
Bit Name
Width /
Bits
Register Name
Actual Acceleration / Deceleration VAX 25 ISM
xVAR0CFGn
Actual Speed VAS 25 ISMxVAR1CFGn
Previous Iteration Speed VPS 25 ISMxVAR2CFGn
Temporary Calculator Register PT1 VPT 25 ISMxVAR3CFGn
Actual Position, Current Result VAP 25 ISMxVAR4CFGn
Virtually Displayed Position VVP 25 ISMxVAR5CFGn
Direction Flag VDR 1 ISMxVAR6CFGn
Speed Flag VSP 1 ISMxVAR7CFGn
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