taken from the manual
in addition to input pins 10 to13 +15 you have on the first printerport
on the second printer port pins 2 to 9 are bidirectional that can be either 8 inputs or 8 output
the C22 MPG interface has 13 LEDs showing the logic levels on the inputs and 1 LED for the output pin 1
assuming the A & B outputs of the MPG are connected to pins 2 & 3 the LEDs 2 & 3 should flicker as its rotated
for 6 out of the 7 positions of the axis select switch 1 of 6 LEDs should be on
for 3 positions of the rate select switch 1 of 3 LEDs should be on
John