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NHET pins output status control question

Fumin Li
Intellectual 510 points

In our project, we use NHET instruction program to control three motors: motorA, motorB, motorC.

Now, in some conditions, for example, if i want to directly control motorA pins ouput value by application code (C code) not by NHET program,  and motorB and motorC still control by NHET instruction program. And some times, all motor control by NHET program.

Because now we have used almost 115 instructions in NHET program, so, i don't want to implement this requirement in NHET instruction program. I want to keep motorA nhet instructions work in normal and not to update the instruction data/control fields.

 

Is it supported in NHET registers like this: if bit in reg.A is configure to disable, then nhet pin output is controlled by NHET program, otherwise, nhet pin output is controlled by output registers.

In NHET registers , i see this NHET pin disable register (HETPINDIS, 0xFFF7 B894), but i not try it. Is this register can implement this requirement? and is there anything i need to pay attention while implementing this requireement ? Thanks a lot.

  • 0
    TI__Genius 13810 points

    If you did not use GIOA0 in your project (this pin is not compatiable in TMS570LS3x devices), let's discuss if it can fit your application. Please make sure the pull option of the NHET pin makes the MOS FETs to turn off.

    Look at the figure below, once the HETPINDIS.x is '1', the output buffer of pin x will be disabled if GIOA0 goes high. GIOA0 can either be driven by the GIOA0 buffer itself or an external signal.

    However, in this case the output buffer is disables, so that, you can not 'output' even through the GIO structure. You application can only pull up/down the pins.

  • 0 in reply to Haixiao Weng
    Intellectual 510 points

    Hi Haixiao,

    What's the meaning of these sentences? I didn't catch it.

    1. what is makes mos fets to turn off ? "Please make sure the pull option of the NHET pin makes the MOS FETs to turn off. "

    2. "However, in this case the output buffer is disables, so that, you can not 'output' even through the GIO structure. You application can only pull up/down the pins."

  • 0 in reply to Fumin Li
    TI__Genius 13810 points

    Fumin Li said:

    Hi Haixiao,

    What's the meaning of these sentences? I didn't catch it.

    1. what is makes mos fets to turn off ? "Please make sure the pull option of the NHET pin makes the MOS FETs to turn off. "

    HW: Once you disable the output buffer, the IO (HET) pin status depends on the pull up / down options. Usually, in such a state, you do not want any volatage apples to motor / high / low side driver, right? For example, in the nMCB board you received from TI, you should pull up the HET pins, then, once the output buffer is disabled, the HET pin voltage is high (by pull up), which shut down the MOS FETs (that drives the motor). In most C2000 development kits, you should pull down HET pins to turn off the MOS FETs.

    2. "However, in this case the output buffer is disables, so that, you can not 'output' even through the GIO structure. You application can only pull up/down the pins."

    HW: Our HET pins can be driven either by the HETDSET, HETDCLR or the instructions. The pin status reflects the latest action (it can be a write to HETDSET/DCLR or a instruction). However, both method requires the output buffer has to be enabled. Once the output buffer of HET is disabled,  it is only an input pin with pull up / down.