OK. I have a more complete view of what is happening and have solved the immediate problem. My previous description of the problem was incomplete; the issue effected all three axes. However, I want to explain the whole situation, the solution as currently deployed, and get feedback on the whole.
By observing the status LEDs on the PMDX board, I could see that the DIR signals for the 3 axes go HI or LO depending on the most recent direction the axis was told to move (I say TOLD, because even if the axis is not moving, the DRO says it is). If the axis moves in the minus (-) direction, the DIR signal stays HI; move in the plus(+) direction and DIR goes LO. If I move two of the three axes (say X &Y) in the minus direction (2 of the 3 DIR signals are HI) I can move both X & Y simultaneously in any combined direction in the proper fashion. But when I tried to move X & Z or Y & Z in the combined minus,minus (-,-) direction, (Thus all three DIR signals are HI when -,- is tried) one or both stutter and lose their position.
More concisely stated, if all three DIR signals are HI, then the combined-axis moves will fail.
Additional notes:
1) The brightness of ALLthe LED status indicators dim further for each HI DIR signal displayed. (This seemed rather suspicious to me, but I'm a bit ignorant of such things).
2) If all three DIR signals are HI, then the X & Y will move in the minus direction if moved individually. However, the Z-axis will not move; it will only move small increments (a few degrees) in the minus direction.
3) I also noticed that Pins 8 and 9 on the breakout board controlling X, Y, & Z were both HI but unused.
I was a bit curious on Pins 8 & 9, and decided that they realy did not need to be lit up and using current. I went into Ports & Pins/Outputs and configured two of the OUPUTS as enabled, and set to Port1 , Pins 8 & 9, and Active LOW. Then after doing the RESET, pins 8 & 9 were off. OK, great. I then tested the axis moves and all three Axes move in any desired combination; even all three at the same time in the minus direction.
I am a bit mysitifed by this behavior, but I'm quite sure someone can explain why this was happening, and I would like to hear that explanation. But more to the point, is this indicative of some other problem I have not uncovered??? Is there some circuit that is drawing more current than it should? I have the 5 volt circuit fused at 1 amp, but maybe that means nothing.
Thanks for wading through the details here. Feedback greatly appreciated on this one!!!
David