Mesa 7i76e - setting output I/Os pull down (low)

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27 Jun 2022 08:25 #245985 by raychar
In using two expansion ports, some I/Os are set as output modes, they are pulled up (at 5V) by default. Wanting them to be pull-down, by moving the  on-board jumper W4 downward, but they are still the same. Is it possible to make them to change? 

Thanks

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27 Jun 2022 12:11 #245994 by tommylight
We are talking about the 26 pin headers, right?
To have them pulled low after LinuxCNC starts, just invert them in hal.
If you need them low at power up, then maybe PCW knows how, but i am pretty sure in the manual it says they are high, so should be taken into consideration during circuit design.
Using ULN2008 can invert them, or any CMOS or TTL inverter chips, can also be done with transistors and resistors.

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27 Jun 2022 13:05 #246005 by raychar
I might not describe in through picture, here are as follow:

1) when computer and mesa card powered up, the I/Os which set as output on two expansion connectors are at high (5v)
2)Once Linuxcnc clicked and loaded, they go to low (0v).
3)there is no significantly effect on them when I flip down the on-board jumper W4.

what my concern is to change 1) to have them at low(0v), so there no high and low swapping
As I have a high current circuit to be controlled, the going high and then low will make make the mosfets blew out (because the swapping of polarity on relay and the sudden through output of high current to dc motor have chance to blow them out)

Thanks,

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27 Jun 2022 13:24 #246006 by tommylight
Moved to "driver boards".

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27 Jun 2022 13:43 #246008 by raychar
don't understand?

another way is charge pump circuit? but a bit complicated

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27 Jun 2022 13:45 #246009 by tommylight
I moved this topic to another section as this is the section that PCW monitors, he is the owner of Mesa and is very, very helpful, always.

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27 Jun 2022 21:53 - 27 Jun 2022 21:54 #246025 by PCW
The expansion connector outputs on a 7I76E will always be high at power on,
when linuxCNC is not running, or after a watchdog bite.
To use them for power switching, your external devices should be active low.

Suggestion: use an OPTO with the LED anode connected to expansion connector 5V
and cathode to the 7I76E GPIO output, then set the GPIO the attribute to inverted for
that GPIO.

Now, the OPTO will be off until LinuxCNC is started _and_ the GPIO hal pin is set high
Last edit: 27 Jun 2022 21:54 by PCW.

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28 Jun 2022 10:38 #246068 by raychar
thank you, it should work and I will get it try asap

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