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CC2642R-Q1: MISO abnormal pull down when CS set high

Simon Huo
Intellectual 1770 points
Part Number: CC2642R-Q1
Other Parts Discussed in Thread: SYSCONFIG

Hi Engineers,

My customer report a problem of CC2642R-Q1. They use a safety chip connected to CC2642 with SPI. And they found when CS is set to high, the MISO is "half pulled down" They are wondering if this is an action of CC2642. Below is their test steps:

1. use CC2642 launchpad and connect to this safety chip with SPI. Same problem happens.

2. disconnect safety chip and CC2642. Just test the MISO of safety chip. Only found PULL UP. This result matches their safety chip vendor's statement.

Support needs: Is that a feature of CC2642?

  • 0
    TI__Guru**** 202096 points

    Hi Simon,

    Can they share their SDK version, SysConfig module SPI configuration, and SPI initialization code?  What is the level of the CC2642R-Q1 device's MISO line when not connected to the safety chip and CS is pulled high?

    Regards,
    Ryan

  • 0
    Prodigy 120 points

    Hi Simon,

    MISO is not only pulled half way down, when CS is high, but also pulled half way up, as shown in the other 2 high pulses of CS.

    Maybe the safety chip requires CS to be active low? In this case MISO would be high-z, when CS is high.

    Having a pullup on the safety chip and (accidently) a pulldown on the controller may cause this behaviour?

  • 0 in reply to Gabiel S.
    TI__Intellectual 1770 points

    Hi Gabiel,

    Sorry for late response. For MISO pin, a weak pull-up from the safety chip causes MISO to be pulled high when CS is high, but because of its weak pull-up capability, it's only half-height. That is why the next few waveforms are half-height.

     Currently, when CS is low, the entire SPI communication is normal, and when CS is high, the SPI is in Idle state. When the MISO pin of the CC2642 and the security chip is disconnected, the MISO pin on the CC2642 side is normally low

  • 0 in reply to Gabiel S.
    TI__Intellectual 1770 points

    Hi Gabiel,

    Sorry again for late response but I just update 2 days ago. Could you please check again? Or should I come up with a new thread.

  • +1 in reply to Simon Huo
    TI__Guru**** 202096 points

    Hi Simon,

    We have established that the SPI is idle when the CS pin is high, and that the MISO pin is weakly pulled up to half-height when the CS pin is high.  When disconnected, the MISO pin of the SimpleLink device is not pulled and thus low whereas the safety chip is pulled high.  The pin behavior during the idle state is dependent on both devices, inside the project's SysConfig the SimpleLink MISO is typically configured as a input with no pull when not in use.

    Regards,
    Ryan

  • +1 in reply to Simon Huo
    Prodigy 120 points

    Hi Simon,

    sorry for my late reaction.

    Just as Ryan mentioned, please check in the controllers SysConfig for the pin configuration, when the pin is not in use. It should not be pulled down.

    Kind regards

    Gabriel

  • 0 in reply to Simon Huo
    Prodigy 120 points

    great to see your problem is solved :)