TMC211 DATASHEET (V. 1.04 / January 7, 2005)
49
7.3 Using the device
Q: What is the meaning of the ‘Shaft’ bit?
A: The Shaft bit determines the rotating direction of the motor, i.e. clockwise or counter-clockwise
rotation.
Q: How to generate an interrupt when the target position is reached?
A: This is not possible. The device hasn’t any interrupt output at all. Just poll ActPos or Motion[2:0]
using an appropriate command.
Q: How can I ensure that I always get consistent data for ActPos and ESW?
A: This is ensured by design. ActPos and ESW are latched synchronously by the same internal signal
edge. The update period is about one millisecond (typ. 1024 µs). Each time ActPos and ESW are read
by the GetActualPos command the result will be a snapshot of both values taken at the same point in
time.
Q: How to specify a second target position to go to immediately after a first target position has
been reached?
A: This is possible using the RunInit command. Note, that after the second target position has been
reached the internal position counter ActPos is reset to zero.
Q: Is it possible to change Vmax on-the-fly?
A: Yes, it is, if the new velocity is in the same group as the old one (see Vmax Parameters). Otherwise
correct positioning is not ensured anymore. Vmax values are divided into four groups:
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•
•
•
group A: Vmax index = 0
group B: Vmax index = 1, 2, 3, 4 ,5 or 6
group C: Vmax index = 7, 8, 9, 10 ,11 or 12
group D: Vmax index = 13, 14 or 15
Q: Is it possible to change the stepping mode on-the-fly?
A: Yes, it is possible and it has immediate effect on the current motion.
Q: How to operate in continuous velocity mode rather than positioning (ramp) mode?
A: There is no velocity mode. The device was designed primarily for positioning tasks so for each
motion there has to be specified a target position by the respective command. However, velocity mode
can be emulated by repeating the following two commands again and again:
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•
Read ActPos using GetActualPos command
Set lower 16 bits of [ActPos+32767] as the next target position using SetPosition command
For real continuous motion this sequence has to be repeated before the current target position has
been reached.
Q: Which units, formats and ranges does position information have?
A: All 16-bit position data fields in commands and responses are coded in two’s complement format
with bit 0 representing 1/16 micro-steps. Hence a position range of –32768…+32767 in units of 1/16
micro-steps is covered regardless of the selected stepping mode (1/2, 1/4, 1/8 or 1/16 micro-stepping).
The difference between the stepping modes is the resolution resp. the position of the LSB in the 16-bit
position data field: it’s bit 0 for 1/16, bit 1 for 1/8, bit 2 for 1/4 and bit 3 for 1/2 micro-stepping. The
position range can be regarded as a circle since position –32768 is just 1/16 micro-step away from
position +32767. The device will always take the shortest way from the current to the target position,
i.e., if the current position is +32767 and the target position is –32768 just 1/16 micro-step will be
executed. 65535 1/16 micro-steps in the opposite direction can be achieved for example by two
consecutive SetPosition commands with target positions 0 and –32768.
The 11-bit secure position data field can be treated as the upper 11 MSBs of the 16-bit position data
fields described above with the 5 LSBs hardwired to zero. Hence it covers the same position range with
a reduced resolution: The position range is –1024…+1023 in units of two full-steps.
Copyright © 2004-2005 TRINAMIC Motion Control GmbH & Co. KG
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
