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AD5271 Daisy Chain Issue, is res pull needed on last device?

Question asked by riscy0000 on Feb 23, 2015
Latest reply on Feb 23, 2015 by msamera

HI

 

I have two device in daisy chain as per schematic (Figure 44), I have 4K7 resistor between two device just as per schematic in Fig 44.

 

I have read the description under "SDO PIN AND DAISY-CHAIN OPERATION", it say nothing about SDO O/P on final stage so I left it open....

 

I implemented that diagram in the project and found last device did not work.I check the SPI bus and the serial comm which in accordance to the data transfer protocol ie SPI CLK and Phase and data......but last device still not work.

 

After reading the datasheet again, it now say.....in page 10

 

" Serial Data Output. This pin can be used to clock data from the shift register in daisy-chain mode or in readback mode. This open-drain output requires an external pull-up resistor even if it is not use. "

 

Why the Figure 44 diagram did not reflect this extremely essential requirement as per page 10?, it did not say the device would not work without this.

 

If they included resistor on SDO on final stage in Figure 44, this issue would not happen.....why it left out?

 

Extremely annoyed.

 

R.

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