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Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!ames!ptsfa!well!ch
From: ch@well.UUCP
Newsgroups: sci.electronics
Subject: Re: 6526 CIA chip problems?
Message-ID: <2806@well.UUCP>
Date: Sat, 21-Mar-87 08:04:17 EST
Article-I.D.: well.2806
Posted: Sat Mar 21 08:04:17 1987
Date-Received: Sun, 22-Mar-87 14:57:36 EST
References: <1097@cavell.alberta.UUCP>
Reply-To: ch@well.UUCP (Chris Hayes)
Followup-To: comp.sys.cbm
Lines: 35


	You're hooking up to a 6526 in the 1541?  Does FLASH! add a 6526
to the 1541 or are you connecting to a 6522?

What hardware changes to the 1541 are there with FLASH!?

What quality wire/cable are you using?  Maybe you need something with
better shielding...

There's nothing you can do about the problem with having one drive
turned off--So keep the other drive on or disconnect the cable from
that drive.

Make sure you don't remove the pullup resistors in the C64.


	Something else about the 6526:  There's a bug with the timer
interrupts--If you are polling the interrupt control register to check
for an underflow instead of responding to IRQs (IRQ masked), the read
of the ICR can clear the underflow bit before it is set, so the
underflow won't be detected...


With open-drain (or collector, as the case may be..) devices, it is
an absolute necessity that there be a pull-up resistor to +5V on
the outputs of all lines.  If you removed the pins of the 6526 inside
the 64 from their sockets, (bypassing the pull-ups and the USER PORT
connector), make sure that there are pull-ups for the lines in one
of the drives.

Hope this helps,
-- 
	Chris Hayes
			UUCP: ucbvax!dual!well!ch
			 OR : {hplabs, ptsfa, lll-lcc}!well!ch