Datasheet

TMC220X, TMC222X DATASHEET (Rev. 1.02 / 2017-MAY-16) 19
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4 UART Single Wire Interface
The UART single wire interface allows control of the TMC22xx 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 danger of wrong or missed commands even in the event of electro-magnetic
disturbance. The automatic baud rate detection makes this interface easy to use.
4.1 Datagram Structure
4.1.1 Write Access
UART WRITE ACCESS DATAGRAM STRUCTURE
each byte is LSB…MSB, highest byte transmitted first
0 … 63
sync + reserved
8 bit slave
address
RW + 7 bit
register addr.
32 bit data
CRC
0…7
8…15
16…23
24…55
56…63
1
0
1
0
Reserved (don’t cares
but included in CRC)
SLAVEADDR=0
register
address
1
data bytes 3, 2, 1, 0
(high to low byte)
CRC
0
1
2
3
4
5
6
7
8
…
15
16
…
23
24
…
55
56
…
63
A sync nibble precedes each transmission to and from the TMC22xx and is embedded into the first
transmitted byte, followed by an addressing byte (0 for TMC22xx). 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 bytewise. The 32 bit data words are
transmitted with the highest byte first.
A minimum baud rate of 9000 baud is permissible, assuming 20 MHz clock (worst case for low baud
rate). Maximum baud rate is f
CLK
/16 due to the required stability of the baud clock.
The slave address SLAVEADDR is always 0 for the TMC22xx.
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.
UART