Hi,
reuelt commented:
Input from Limit/home switches etc. can use HIGH voltage and so through opto-isolation chips (sort of relay) for safety reason. The PC USB is grounded with with PC case so USB is NOT isolated from PC.
This is potentially misleading. I have attached the representative digital inputs (DB25 pins 10,11,12,13,15) and none of them are
optically isolated. If you put more than 5V on any of them you will fry the buffer IC. DO NOT USE 24V INPUTS unless you
make and provide some voltage translation. Exceed 5V input to 74LS TTL IC's frys them!
I have also attached pics of the digital outputs (DB25 pins 14,16,17) and the motor outputs (DB25 pins 2,3,4,5,6,7,8,9)
and they are not opto-isolated either.
This has implications.
First one and one only 5V supply is needed. It can be derived is different ways but still only one supply is required.
Under no circumstances apply more than 5V to any input.
Do not demand that any output exceed sink or source current appropriate to 74LS TTL. To be safe no more than 10mA
sinking or sourcing.
Craig