TMC2041 DATASHEET (Rev. 1.02 / 2017-MAY-16)
20
5.2 CRC Calculation
An 8 bit CRC polynomial is used for checking both read and write access. It allows detection of up to
eight single bit errors. The CRC8-ATM polynomial with an initial value of zero is applied LSB to MSB,
including the sync- and addressing byte. The sync nibble is assumed to always be correct. The
TMC2041 responds only to correctly transmitted datagrams containing its own slave address. It
increases its datagram counter for each correctly received write access datagram.
퐶푅퐶 = 푥8 + 푥2 + 푥1 + 푥0
SERIAL CALCULATION EXAMPLE
CRC = (CRC << 1) OR (CRC.7 XOR CRC.1 XOR CRC.0 XOR [new incoming bit])
C-CODE EXAMPLE FOR CRC CALCULATION
void swuart_calcCRC(UCHAR* datagram, UCHAR datagramLength)
{
int i,j;
UCHAR* crc = datagram + (datagramLength-1); // CRC located in last byte of message
UCHAR currentByte;
*crc = 0;
for (i=0; i<(datagramLength-1); i++) {
currentByte = datagram[i];
// Execute for all bytes of a message
// Retrieve a byte to be sent from Array
for (j=0; j<8; j++) {
if ((*crc >> 7) ^ (currentByte&0x01))
// update CRC based result of XOR operation
{
*crc = (*crc << 1) ^ 0x07;
}
else
{
*crc = (*crc << 1);
}
currentByte = currentByte >> 1;
} // for CRC bit
} // for message byte
}
5.3 UART Signals
The UART interface on the TMC2041 has following signals:
TMC2041 UART INTERFACE SIGNALS
SWIOP
SWION
Non-inverted data input and output
Inverted data input and output for use in differential transmission. Can be left open
in a 5V IO voltage system. Tie to the half IO level voltage for best performance in a
3.3V single wire non-differential application.
NEXTADDR
SDO
Address increment pin for sequential addressing scheme
Configuration input: Tie low for standard mode!
In UART mode (SW_SEL high) the slave checks the single wire SWIOP and SWION for correctly
received datagrams with its own address continuously. Both signals are switched as input during this
time. It adapts to the baud rate based on the sync nibble, as described before. In case of a read
access, it switches on its output drivers on SWIOP and SWION and sends its response using the same
baud rate.
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