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DAC8750: CRC error

Jiri Kastan
Prodigy 10 points


Hello, i have problem with CRC communication also.
I am followotn this procedure.
1. sends Control register to 0x1007
2. sends Config register to 0x0008
3. switch on CRC computing - go to 32 bit frame
4. Sends dac value frame as 0x01 7B 20 BE
verify status register - the CRC-FLT bit is set., the Control register has 0x1007.
5. sends reset register to 1.
6. switch off CRC - go to 21 bit frame
7.repeat point 1) 2) 3)
8. read status register - 0x0000
9. write dac value as in point 4). but no change on the current output.
10. read status register - it takes 0x0000.
the output just jumps to current 0.73mA .

When i do the procedure without CRC setting - point 2) is skipped and frame is just 24bit. The output goes in whole range 0-24mA.
Any ideas what is wrong?
  • 0
    TI__Mastermind 46290 points
    Jiri,

    In steps 1, 2, and 3 what is the number of clock pulses in the SPI frame? 24-bits? Has anything else been written on the bus prior to these steps?

    The CRC value you sent in step 4 is correct for the data you sent, so the CRC flag should not be triggered in the status register. Did the DAC output respond as expected after step 4? It is interesting to me that the issue would be isolated to just the DAC data register since you appear to be able to issue read commands successfully. If you issue a read command without sending data to the DAC data register does the status flag also get triggered?

    In step 7 you have repeated everything and returned into the CRC mode? Would steps 8 through 10 also be with the CRC mode enabled?