I’m in the process of designing a circuit to control four 18v25 CS motor drivers from a Teensy 3.2. I’ve almost got everything setup and working perfectly, but I’m having difficulty reading the fault codes.
I’m using a Microchip MCP23017 I/O extender running at 5v (because there aren’t enough pins on the teensy) to read the fault flags for the 4 controllers. Each of these lines is pulled up to 5v with a 4.7k resistor. I tried this without pull-up resistors and the ‘high’ signals from the motor controller where around 1v.
The strange behaviour I’m seeing is that both the FF1 & FF2 lines are identical. I’m able to test the under-voltage and short-circuit faults easily but both fault conditions result in FF1 & FF2 going high. If the voltage was low and I increase it back to 14v then both flags go low and the driver starts working again. I the short circuit fault was triggered, then a reset gets the board going again and sets both flags to zero.
Also strangely if I pull the reset pin low to disable the motor controller both the fault flags go high, in a case where there is not fault! It appears that both FF lines are high when the driver is disabled/off and low when it is running
I’ve tested the impedance between the two fault flag pins with the driver taken out of the circuit and I get 94k ohms, is this the expected value?
Does anyone know what’s going on here? What is the recommended circuit to read these fault lines?