TMC428_06 Datasheet, PDF (28/58 Pages) List of Unclassifed Manufacturers – Intelligent Triple Stepper Motor Controller with Serial Peripheral Interfaces

TMC428 DATASHEET (v. 2.02 / April 26^th, 2006)
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The CDGW (= Cover DataGram Waiting, see section 9.3 on page 28) status bit is set to 1 until a
datagram is received from the stepper motor driver chain. For read out of datagram_low_word and
datagram_high_word the CDGW status bit is important to be able to detect when a datagram transfer
has been completed after an initial write to one of the two registers. The fact that the CDGW is formed
by logical OR between the cover datagram status and the status of the datagram_low_word and
datagram_high_word causes no restriction concerning its usage. This is because a write to the
cover_datagram register forces sending a datagram which results in an update of the
datagram_low_word and datagram_high_word registers. One the other side, if the
cover_datagram mechanism is not used, the CDGW status bit is exclusively available as the status
signal of datagram_low_word and datagram_high_word.
9.2 cover_pos & cover_len (JDX=%0010)
The TMC428 provides direct sending of datagrams from the microcontroller to the stepper motor
drivers. This may be necessary for initialization of different driver chips and useful for reconfiguration
purposes. A datagram with up to 24 bits can be transferred to the stepper motor driver by covering one
datagram sent to the driver chain. The parameter cover_pos defines the position of the first datagram
bit to be covered by the cover_datagram (JDX=%0011) of length cover_len. In contrast to the
datagram numbering order of bits, the position count for the cover datagram starts with 0. The
cover_datagram bits indexed from cover_len-1 to 0 cover the datagram sent to the drivers chain.
Important Note: A step bit used to control stepper motor drivers must not be
covered while a motor is running.
This is because the coverage of a step bit would cause losing that associated step if the step bit is
active. The TMC428 stores cover_pos+1 instead of cover_pos due to internal requirements. So, one
writes cover_pos but reads back cover_pos+1. The cw (= cover waiting) bit available by read out of
this register. The CDGW status bit (see section 9.3) is the result of logical OR between cw and an
internal signal that indicates the status of the stepper motor serial driver chain send register.
9.3 cover_datagram (JDX=%0011)
This register holds up to 24 bit of a cover datagram. A cover datagram covers the next datagram sent
to the stepper motor driver chain. If no datagrams are sent to the drivers chain, the cover datagram is
sent immediately if a cover datagram is written into this register. The status of the cover datagram is
mapped to the status bits sent back with each datagram (see Table 6-4, page 12, CDGW status bit).
This status bit is also available for readout of cover_pos & cover_len (JDX=%0010), where CDGW is
the most significant data bit (23).
48 datagram bits send to the stepper motor driver chain
position=39: cover_pos = 39
datagram bits #39 to #46 covered by cover_datagram bits #6 to #0
39 40 41 42 43 45 46
0 1 2 3 4 5 6 7 8 9 10 11 12
34 35 36 37 38 6 5 4 3 2 1 0 47
cover datagram bits #6 to #0 cover the 7 datagram bits #39 to #46
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 ⁶ 5 4 3 2 1 ⁰
(MSB)
(LSB)
MSB of the cover datagram (here bit #6) is sent first.
length = 7: cover_len = 7
Figure 9-2: Cover datagram example
up to 24 cover_datagram bits
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