Open Drain GPIO ?

[brad]

Hi,
Can the Sub20 devices be configured to operate in open collector configuration? ie if output is disabled (low), then pin has high impedance.

Thanks,
Brad

[brad]

I looked in the manual for the Atmel processor on my sub20.... looks like the GPIO can have its internal pullup resistor disabled.

[xol]

Sure. You can configure SUB-20 GPIO as input with or without pull-up
Take a look here:
http://www.xdimax.com/sub20/doc/HTML/gpio_functions.htm
We impose via API all functionality available in CPU.

[brad]

Thanks for the reply. Unfortunately I wasn't specific enough in my original post.
I would like the "fPWM" module to be open-collector... this is SPI pin #4. I could also use the 8-bit PWM module but not as desirable.

I am trying to pull down a 6.5V high-impedance load with the PWM signal. When PWM DC is 0% then the load shouldn't be pulled down.

[xol]

Well with Fast PWM it is not possible as we use for Fast PWM HW module that do not have open-drain output.
So I see two possible solutions:
1.You can use external transistor to convert output to open-drain. If you need we can provide reference schematics.
2. With a FW modification I can give you open-drain output on 8-bit PWM
What do you think?

[brad]

I'll look into using the 8-bit PWM for my application.
Can you provide me the example external-transistor circuit you offered?
Thanks.

[xol]

Here are two options:

NPN Transistor

2N2222.jpg (24.36 KiB) Viewed 16975 times

N-channel MOSFET

2N7002.jpg (28.19 KiB) Viewed 16975 times

Consider the fact that

IN="0" OUT= Open Drain
IN="1" OUT= "0"