68010 source?

[DoN Nichols]

In article <1991Feb22.063455.436 at texrex.uucp> rmfowler%texrex at cirr.com writes:
>Where can I get a 68010 and how much would it cost me?

	I've gotten them from chip dealers at hamfests for about $30.00.
There are dealers who sell chips in some of the bigger magazines.  Look for
multi-page ads.

>I just ran diagnostics on the processor and I am getting an error
>on the 60 Hz clock test.  Maybe THIS is the cause of my crashes.
>(But I thought you fixed that by removing your mouse? you say)
>Well the mouse must have been a coincidence because the crashes have
>resumed.

	Are you sure that this is testing the cpu CHIP?  I think that the
60Hz clock comes from other hardware on the cpu BOARD.  The 60Hz clock
generates interrupts to the cpu chip, so it could be a problem with the
hardware generating the interrupts (perhaps a double interrupt too close
together), or a problem in the cpu chip's response to the interrupts.  I
consider the chip to be unlikely, but it is fairly simple to replace (once
you get to it :-).  You might look at the interrupt pin in question with an
oscilloscope.  OOPS!  Looking at the tech ref man, the interrupt is encoded
into three pins (from seven possible intrrupts).  It could be the encoding
circuitry that isn't working properly.  A glance at the intrrupt lists shows
interrupt 6 as being the realtime interrupt.  I suspect that this is the one
in question.  Yes, looking at thr schematics shows the 60Hz interrupt coming
into the encoder (IC 18F) at pin 3, which is level 6.  It is tied in with
the VSync signal for the video, and comes from IC-28H, pin 9.  Input is pin
10 (from the Vsync signal), reset at pin 11.  The reset comes from IC-27B,
pin 12.  This is the same chip which drives the leds on the side of the cpu
box.  Look for a 60Hz pulse present on each of the pins listed.  If one of
these is missing, this is a clue as to which chips/signals are not working.
(But it may be only occasionally missing).

>
>Thanks


	You're welcome, and
		Good Luck
			DoN.


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