An A319's number two and three Display Management Computers (DMC) apparently failed simultaneously causing the First Officer's PDF; ND and Lower E/WD screens to alternate from a normal display to a white diagonal bar.

Narrative

During cruise flight at FL380 in clear skies we got a Master Caution warning and ECAM regarding EIS DMC #2 failure directing us to switch the First Officer to DMC #3. The problem we had was that the ECAM would display then clear itself repeatedly and uncontrollably about every 2 to 3 seconds and at times even faster. The First Officer's ND; PFD; and Lower E/WD screen were going from normal display indications to diagonal lines across them at the same pace as the ECAM displaying and clearing it. You couldn't silence the master caution or use the emergency cancel to silence the warning because it was resetting then reappearing repeatedly. We set the First Officer DMC to #3 but that gave us the same indications that we viewed in the normal DMC position (First Officer on #2) the only difference was that First Officer DMC on #3 displayed no air data display. Basically the problems with DMC #2 went to DMC#3 when DMC was switched to First Officer on #3. Switching air data to the other air data system was no help. The biggest problem was that you couldn't keep any system pages or an ECAM page displayed long enough to use it before it would clear itself or you would get diagonal lines through the screen. If you held the button for a system page the display would show for a second then move to the Upper E/WD screen or show diagonal lines through the lower screen; it basically was uncontrollable as well. You couldn't get readings for any system except engine parameters on the upper screen for any significant amount of time. This was my greatest concern because we wouldn't be able to get trough any ECAM or check any system should we need to. We contacted dispatch and maintenance through a commercial radio service to discuss our situation. Maintenance looked through his procedures since we had none on our aircraft to deal with this problem. The only thing he could provide was for me to exercise my Captain's emergency authority to reset some circuit breakers in flight which I elected not to do since I felt that we technically were not an emergency aircraft at the time based on our position and the weather. However I did understand that I had no way of effectively monitoring systems or dealing with a system failure or ECAM with our current situation which I stated to maintenance and dispatch. We elected to divert to seek assistance for the aircraft and passengers. We continued to the divert airport and landed without further incident. We met maintenance; the Customer Service Representative; and the base Assistant Chief Pilot to discuss the problem and try to get the aircraft repaired so that we could continue. Maintenance attempted a repair put it was decided that the aircraft would be taken out of service.