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TMC211 DATASHEET (V. 1.04 / January 7, 2005)
7 Frequently Asked Questions
7.1 Using the bus interface
Q: How many devices can be operated on the same bus?
A: 128 devices can be discriminated by means of the physical address. However, it depends on some
factors if this high number really makes sense. First of all it has to be checked if each device can be
serviced under any circumstances in the maximum allowed time taking the bus speed and the
individual real-time requirements of each device into account. Second, the idea of reserving address 0
for OTP physical address programming during system installation and defective parts replacement
reduces the number to 120. Third, the TMC211 has faster and slower types of the GetActualPos,
GetStatus and SetPosition commands. The faster types of course can satisfy harder real-time
requirements but can only be addressed to 8 different physical devices. If the faster types shall be
used only 8 TMC211 devices can be connected to the same LIN bus.
Q: How to program the OTP physical address bits of a device if there are more devices
connected to the same bus?
A: The problem here is that all new devices are shipped with the OTP physical address bits set to zero
making it difficult to address just one device with the SetOTPParam command. Use HW0, HW1 or
HW2 input as chip select line to address just one device by SetOTPParam. If this is impractible since
the HW0/HW1/HW2 inputs are hardwired or not controllable for any other reason the only alternative is
to assemble and program one device after the other. I.e., assemble only first device and program the
desired non-zero address, then assemble the second device and program the desired non-zero
address, and so on until all devices are assembled and programmed. This is also a good service
concept when replacing defective devices in the field: The idea is that all devices are programmed to
different non-zero physical addresses at production/installation time. Once a defective device is being
replaced the replacement part can easily be addressed by SetOTPParam since it is the only part with
physical address zero.
7.2 General problems when getting started
Q: What is the meaning of ElDef?
A: The ElDef flag (‘Electrical Defect’) is the logical ORing of the OVC1 and OVC2 flags. OVC1 is set to
one in case of an overcurrent (coil short) or open load condition (selected coil current is not reached)
for coil A. OVC2 is the equivalent for coil B.
Q: What could be the reason for ElDef / OVC1 / OVC2 being set to one?
A: There are a number of possible causes:
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Motor not connected (Æ open load)
Connected motor has shorted coils (Æ overcurrent) or broken coils (Æ open load)
Motor coils connected to the wrong device pins
Selected coil current can not be reached (Æ open load) due to high coil impedance or low
supply voltage. Solution: Select a lower coil run/hold current or rise the supply voltage.
Generally: the calculated voltage required to reach a desired coil current at a given coil
resistance (V = I • R) must be significantly lower than actual supply voltage due to the coil
inductivity.
Q: Should the external switch be normally closed or open when the reference position is hit?
A: The SWI input resp. the ESW flag have neither effect on any internal state machine nor on
command processing, even not on the RunInit command. ESW must be polled by software using
GetActualPos or GetFullStatus commands. The software can simply be adapted to whatever state the
switch is in when the reference position is hit, i.e. closed or open.
Copyright © 2004-2005 TRINAMIC Motion Control GmbH & Co. KG
TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
