Written by Jeff Kulczycki - 20 March 2000

QUESTION:  What's with those characters that show up on the score display during initialization?

ANSWER:  Those characters are part of the 68705 Test.  The 68705 (or equivalent circuitry) generates an interrupt to the Z80 Microprocessor every 33ms so that it can keep in sync with the laserdisc player and update relevant timers.  I have seen different versions of ROMs perform this test two different ways.  Early ROMs perform a simple PASS/FAIL test when in diagnostic mode.  This test loops for 32.7ms, and if no interrupt occurs during this time, then it is considered a failure, and the screen shows "68705 TEST FAILED".  Later versions of ROMs remove this test from the diagnostic mode and instead perform it every time the machine starts up.  This later test has a free running counter that starts on one interrupt and stops on the next.  That number is then displayed in the Player 2 score.  The number should be between $0A00 - $15FF hex.  I usually see $0E34.  The result of the test is shown in the Player 1 score... "1" = too fast, "2" = PASS, "3" = too slow.



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