SPI_TX state when C5505 SPI port inactive

AM44866

What is the logic state of the SPI_TX line when inactive, between SPI transactions? We are using a resistor to pull the line to a known state, but would like to make it match the inactive state of the TX line so that we're not burning power over the resistor while the port is inactive (which is the majority of the time due to it's low duty cycle).

Thanks - AM

over 15 years ago

0 Peter Chung over 15 years ago

TI__Expert 8065 points

AM,

Thank you for your email. The SPI-TX state in inactive condition is programable. Pleaes take a look at the SPI user's guide (Mode 0 ~ 3).

http://focus.ti.com/lit/ug/sprufo3/sprufo3.pdf

Regards,

Peter Chung

0 AM44866 over 15 years ago in reply to Peter Chung

Intellectual 275 points

Hi Peter,

In the documentation you referenced, I could only find information with respect to the clock and chip select inactive states, nothing in particular regarding the TX pin. Figures 4-7 would lead me to believe this line may be hi-Z when inactive, could this be the case?

Thanks - AM

0 Peter Chung over 15 years ago in reply to AM44866

TI__Expert 8065 points

Hi AM,

You are correct. I though you were asking about CLK polarity, sorry. I think TX's state will be kept to the last state during inactive period. However, let me double check it and get back to you within this week.

Regards,

Peter Chung

0 Peter Chung over 15 years ago in reply to Peter Chung

TI__Expert 8065 points

AM,

I was wrong. I have verified that the DX pin becomes Hi-Z while CS is high (inactive).

Regards,

Peter Chung

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SPI_TX state when C5505 SPI port inactive