GPIO pin passing current on shutdown

Hi Guys I have some odd behavior on my 7i42TA card.

I have added the following to my custom_postgui.hal file. I am using a low voltage solid state relay to open and close a switch which operates my Z axis drive. When I toggle the button on my gamepad it works perfectly. However when I shut LinuxCNC down. The darn thing re-enables.

So it's like the + PIN is passing a small amount of current through to the - PIN when LinuxCNC is shut down effectively acting like I have toggled the button back on. I would prefer this default state is NOT passing current. -Suggestions welcome!


# --- Zamp-ENABLE ---
setp hm2_7i43.0.gpio.033.is_output true

loadrt toggle count=1
addf toggle.0 servo-thread
net zamp-enable toggle.0.in <= input.0.btn-base4 #START Button on joystick
net zamp-light toggle.0.out => hm2_7i43.0.gpio.033.out

This is expected, if you use a SSR with any FPGA output you should tie the SSR + input to 5V from the 7I42A and the SSR - input to the 7I42TA output

From the 7I43 manual:

STARTUP I/O STATE
When the 7I43 is used to control external equipment that is sensitive to the initial
pin states, the pre-configuration pull-ups should be enabled (W3 UP), and for most
configurations, pull-ups resistor should be configured on any I/O pin that is not driven when
configuration is complete (bi-directional pins and pins whose function is assigned by
software). Since the only definable pre-configuration state is with pull-up resistors on the
I/O, this means the proper I/O polarity is active low (so that all outputs are in the in-active
state at power up)
DRIVING +5V REFERRED LOADS
When driving external loads like Solid State Relays (SSRs) with an active low
output, and the +SSR terminal connected to +5V, the 7I43 output should be configured for
5V tolerance, and the output should be driven in open drain mode. This is because the
7I43 outputs only swing to 3.3V in normal mode, leaving 1.7V (5V -3.3V) driving the SSR
when the output is high and the SSR should be off.

That worked! Thank you Peter...