TMC223 DATASHEET (V. 1.05 / March 7, 2011)
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8 Frequently Asked Questions
8.1 Using the bus interface
Q: How many devices can be operated on the same bus?
A: 32 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 30.
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 HW input as chip
select line to address just one device by SetOTPParam. If this is impractible since the HW input is
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.
8.2 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 (ꢁ open load)
Connected motor has shorted coils (ꢁ overcurrent) or broken coils (ꢁ open load)
Motor coils connected to the wrong device pins
Selected coil current can not be reached (ꢁ 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
GetFullStatus1 command. The software can simply be adapted to whatever state the switch is in when
the reference position is hit, i.e. closed or open.
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