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TMP1827: 64-bit UID CRC8 not correct

Part Number: TMP1827

Hi all,

I'm working with a TMP1827NNGRR. I'm accessing the one-wire bus through UART with a STM32G0B1. So far, everything is working great. I'm able to read temperature, configure the chip via Scratchpad-1, read/write to EEPROM withot any problem. Everywhere a CRC8 calculation is needed, for example when reading the Scratchpad-1, reading EEPROM, etc, my way of calculating the the CRC8 works just perfectly. The only issue I'm having is when I'm reading the 64-bit UID, which is composed of the bytes below (LSB to MSB), the CRC8 I'm calculating never matches the one received from the device :

1 byte device family

6 bytes address

1 byte CRC8, which is calculated from the 7 first bytes of the answer from the TMP1827.

The setup is a single device on the OW bus, bus powered 3.3V, 1Kohm PU resistor, controlled via UART, using standard speed (overdrive speed also works for everything else but this).

The sequence I'm using is :

1. Reset

2. (Write) Read address (0x33)

3. Read 8 bytes

4. Compute CRC8 using the 7 first bytes LSb first with the following code (which works with all the other CRC8 calculations)

uint32_t TMP18XX_Calculate_CRC8(const void *data, uint32_t len)


// Implementation processes LSB first with inverted polynomial to achieve same result.

const uint8_t *d = data;

const uint32_t ipoly = 0x0000008C; // Inverted 0x31

uint32_t crc = 0;



crc ^= *d++;

for(uint32_t k = 0; k < 8; k++)


crc = crc & 1 ? (crc >> 1) ^ ipoly : crc >> 1;



return crc;


Do you have any idea of what could be my problem here?



  • Hi Alfred,

    This is a known problem that some TMP1827 were produced with an incorrect Address CRC. The full 64 bit address, including the CRC byte, is stored in the TMP1827 and not calculated by the TMP1827. During data transmission, the TMP1827 calculates the CRC based on the data sent. This is why your CRC works for transmissions but fails on the address calculation. The Address CRC has already been corrected in production, and future TMP1827 devices will not have this issue. In the meantime, impacted devices can still be communicated with normally by using the 64 bit address as reported by the device. 



  • Hi Ren, that is good news! Is there a way to know the range of serial numbers this issue is affecting?

    Thanks a lot,