TMC2041 DATASHEET (Rev. 1.02 / 2017-MAY-16)
18
5 UART Single Wire Interface
The UART single wire interface allows the control of the TMC2041 with any microcontroller UART. It
shares transmit and receive line like an RS485 based interface. Data transmission is secured using a
cyclic redundancy check, so that increased interface distances (e.g. over cables between two PCBs) can
be bridged without the danger of wrong or missed commands even in the event of electro-magnetic
disturbance. The automatic baud rate detection and an advanced addressing scheme make this
interface easy and flexible to use.
5.1 Datagram Structure
5.1.1 Write Access
UART WRITE ACCESS DATAGRAM STRUCTURE
each byte is LSB…MSB, highest byte transmitted first
0 … 63
8 bit slave
address
8…15
RW + 7 bit
register addr.
16…23
sync + reserved
32 bit data
CRC
56…63
CRC
0…7
24…55
data bytes 3, 2, 1, 0
(high to low byte)
Reserved (don’t cares
but included in CRC)
register
1
0
1
0
SLAVEADDR
1
address
A sync nibble precedes each transmission to and from the TMC2041 and is embedded into the first
transmitted byte, followed by an addressing byte. Each transmission allows a synchronization of the
internal baud rate divider to the master clock. The actual baud rate is adapted and variations of the
internal clock frequency are compensated. Thus, the baud rate can be freely chosen within the valid
range. Each transmitted byte starts with a start bit (logic 0, low level on SWIOP) and ends with a stop
bit (logic 1, high level on SWIOP). The bit time is calculated by measuring the time from the
beginning of start bit (1 to 0 transition) to the end of the sync frame (1 to 0 transition from bit 2 to
bit 3). All data is transmitted byte wise. The 32 bit data words are transmitted with the highest byte
first.
A minimum baud rate of 9000 baud is permissible, assuming 20MHz clock (worst case for low baud
rate). Maximum baud rate is fCLK/16 due to the required stability of the baud clock.
The slave address is determined by the register SLAVEADDR. If the external address pin NEXTADDR is
set, the slave address becomes incremented by one.
The communication becomes reset if a pause time of longer than 63 bit times between the start bits
of two successive bytes occurs. This timing is based on the last correctly received datagram. In this
case, the transmission needs to be restarted after a failure recovery time of minimum 12 bit times of
bus idle time. This scheme allows the master to reset communication in case of transmission errors.
Any pulse on an idle data line below 16 clock cycles will be treated as a glitch and leads to a timeout
of 12 bit times, for which the data line must be idle. Other errors like wrong CRC are also treated the
same way. This allows a safe re-synchronization of the transmission after any error conditions.
Remark, that due to this mechanism, an abrupt reduction of the baud rate to less than 15 percent of
the previous value is not possible.
Each accepted write datagram becomes acknowledged by the receiver by incrementing an internal
cyclic datagram counter (8 bit). Reading out the datagram counter allows the master to check the
success of an initialization sequence or single write accesses. Read accesses do not modify the
counter.
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