ADS8685: Input command word and register write operation

Albert Chen76

Prodigy 230 points

Part Number: ADS8685
Other Parts Discussed in Thread: ADS8691

I'm going to coding FPGA to control ADS8685.

However, the write/read operation is difficult to understanding to me.

1. what's the meaning of the "LSB of the 9-bit address is always ignored and considered as 0b" in Table5?

If the address which i wanna access should valid in the chip. But why it is always ignored??

2. What's the difference of behavior in three types of write command? could you make some example?

Also, which command is useful for what situation?

2.It's better to make some example for all opcode except NOP command.

over 4 years ago

0 Dale Li over 4 years ago

TI__Mastermind 37425 points

Hello Albert,

Please refer to the answer in another thread, ADS8685 has a similar command structure as ADS8691.

https://e2e.ti.com/support/data-converters/f/73/t/886861

Please let me know if you still have questions after check.

Thanks&regards,

Dale

0 Albert Chen76 over 4 years ago in reply to Dale Li

Prodigy 230 points

How about the write command?

if write command for byte 1 of register 04h

could i clock out 24bits clock only for

11010-01 000000100 <8bits> ?

Because of HWORD is stand for half-word means 8 bits.

Does it mean only write 8bits in 8bits if address?

if wanna Write bits 31-24 of reg24h

11010-01 00010-0110 <31-24> <ignore 8bits>

is it right?

how to use SET_HWORD? what’s different between write command?

0 Dale Li over 4 years ago in reply to Albert Chen76

TI__Mastermind 37425 points

Hi Albert,

All input commands used to configure the internal registers MUST be 32-bit long, even you are using Half-word write command, please see the description under Table 5 in datasheet.

You command for bit 31-24 of register address 24h is correct, 26h address should be used in write command, however the rest 8-bit should be included for total 32-bit long command.

Regards,

Dale

0 Albert Chen76 over 4 years ago in reply to Dale Li

Prodigy 230 points

thanks Dale

i'll try it

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ADS8685: Input command word and register write operation