Need help with TB6560

I'm configuring a 5i25 to interface with a parport BoB. It's a YOOCNC-NT65-3X from a YOOCNC 4030 machine.
I've read conflicting information about the step pins, so I'm not sure if they are active-low or active-high (at the DB25).

PDF schematic attached

Here are some quick observations:

• Active-low appears to harder to turn by hand while they are idle. Emits a slight noise from the steppers. The steppers feel hotter.
• Active-high is easier to turn by hand while they are idle. No noise from steppers.

Both seem to "work", but which is correct?

The torque when not stepping should not depend on the polarity of the step pins at all.
Not-stepping should just lock the motor in the last-commanded position.

The schematic shows the pins pulled-up to 5V then inverted by a 74HC14 before being sent to the low-side of an opto-isolator.

I think you might need to work backwards from the TB6560 as it goes through so many inversions on the way.

Yep, I've just been working backwards from the TB6560.

1. The TB6560 steps on a rising edge of the CLK.
2. The 6N137 inverts the signal, but since the input is fed into the cathode the net result is non-inverted.
3. 74HC14 inverts the signal.

Overall, the DB25 step signal would need to be active-low (contradicting the manual).

I'm not sure how to interpret the circuit controlling the torque inputs TQ1 & TQ2. Seems that it toggles the torque signal on step signal? Might have something to do with the heat generated on the steppers for active-low?

After some further analysis, it appears they are trying to control torque by the CLK (STEP) input.

[Refer to attachment]
Orange = CLK
Green = TQ1 & TQ2

TQ1/TQ2 HIGH = 20% torque
TQ1/TQ2 LOW = 100% torque

For the TB6560, stepping occurs on the rising-edge of CLK. The confusing part of all this is that every CLK rising-edge, the torque is at 20%...

Maybe there a fault in their circuit?

LS wrote: Maybe there a fault in their circuit?

It's not impossible. Though they seem to have a lot more of the circuit than is normal, and this might be a sign that they are trying to do a good job.
There is an RC network with an 8µS time constant on the TQ inputs, but that seems too short for a current-lowering circuit (which many drivers use).

Today I used the DMM to perform some basic logic checks on the circuit board. The circuit logic appears to be correct, so it's more likely there's a bug in the schematic diagram instead.

The torque is minimised while idle (CLK=HIGH; TQ=HIGH. When a step command is issued, the CLK goes LOW, which brings TQ LOW (increasing torque), then on the rising edge of CLK a step occurs. I'd say the 8µS time constant holds the torque pin LOW (100% torque) after the rising-edge clock to ensure there is full torque throughout the step action. I'd need to borrow a logic analyser to watch whats going on during operation .. a job for another day.

To answer the original question .. the step pins are active-high.

Cheers
Luke