Mesa 7I76 field input threshold

Hello,
I have a Mesa 7I76 with a Vin of 24V.
The manual says:
"7I76 inputs sense positive input voltages above a preset threshold. For best
general purpose use, default input threshold is 50% of the field power supply voltage with
10% hysteresis. That is with a 24V field voltage an input must be brought to 60% of 24V
= 14.4V to be sensed as high and then brought to 40% of 24V = 9.6V to be sensed as low."

How can I change the preset threshold and hysteresis??
I need, with a 24V field voltage, to read a TTL voltage.

thanks
Frank

The simple answer is you cannot, the default input threshold is 1/2
of the field voltage.

However there are some options

1. If you have a recent 7I76 you can run the field power at 5V (Vin is still needs to be 8V or so) Of course this means the outputs will be 5V outputs as well

2. Are the field inputs for a MPG?, again with a recent 7I76 you have the option of supporting up to 2 TTL level MPG inputs (4 pins)

3. add a 7I73 or 7I69

4. Hound Mesa into supporting a TTL input option on some number of the 7I76 pins

OK, thank you.
Maybe, I build me a level converter.

The manual say also:
"All field input pins are capable of reading the input voltage. These are not highly
accurate or high resolution but can be useful for things like potentiometer inputs. Input
resolution is 8 bits and input full scale value is 36.3V. Accuracy is +-5%
Software process data modes 1 and 2 allow reading the analog voltage on inputs
0 through 3, in addition to the 32 digital bit inputs."

If I can read the analog value of a input pin, I can also read a TTL-level, or not ?


Frank

Sure. I missed that in my list. If you use modes 1 or 2 you have 4 analog inputs that could be used for reading TTL level signals (though just 4)

The comp component can be used to convert the analog value to a bit

OK, I will change the 7I76 to mode 1 with this command:
"sserial_port_0=10xxxxxx"
Then I will have 4 hal pins with the analog values of the input pins 0..3.
Then I can check in the hal-file with "comp" the values with my own threshold.
Is this correct?

Frank

Yep, and thresholds will be in volts

It is running !!!
Here are the extensions in the hal-file:

loadrt hm2_pci config=" num_encoders=1 num_pwmgens=0 num_3pwmgens=0 num_stepgens=5 sserial_port_0=10xxxxxx "
loadrt comp count=1
addf comp.0 servo-thread

net analog0 hm2_5i25.0.7i76.0.0.analogin0
net analog1 hm2_5i25.0.7i76.0.0.analogin1
net analog2 hm2_5i25.0.7i76.0.0.analogin2
net analog3 hm2_5i25.0.7i76.0.0.analogin3

setp comp.0.in1 4.0
net analog3 comp.0.in0
net ESTOP-IN comp.0.out

net ESTOP-IN => iocontrol.0.emc-enable-in


Thank you PCW