Pull Up Confusion in HDK Schematics

Lorenz Gruebler

Other Parts Discussed in Thread: TMS570LS3137

Hello Forum,

I am developing a CPU Card using the TMS570LS3137, in the schematics of the TMS570LS3x/RM5x Hercules Development Card there are 10K Pull Up on each MibSPIxNCSx (R55,R56,R57,R58,R59, R60,R81,...). The Label says VCC_3V3 (Pull Up) and the schematics symbol says GND to me. Anyhow these signals have a default pull state of "Pull Up".

So my questions:

+ Are these resistors Pull Up or Pull Down

+ Why do I need them? (I use the MibSPI1 and MibSPI3 including NCS[n] Pins to connect two TMS570 together by SPI)

regards,

Lorenz

over 12 years ago

0 Kevin Lavery over 12 years ago

TI__Mastermind 20870 points

The resistors are pull-up. The symbol is a bar with a label, although the label is well above the bar and could give an erroneous impression.

Since the nCS[x] pins are active low, the pull-ups keep them in an inactive state. There are internal pull-ups that remain active when the pin is configured as a chip select.

Best Regards,

Forum Support

0 Lorenz Gruebler over 12 years ago in reply to Kevin Lavery

Expert 1075 points

Hello Kevin,

Thank you for answering, so I will add external pull for better signal conditions.

regards,

Lorenz

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Pull Up Confusion in HDK Schematics