Subject: Re: comprobe and a GoldeGateII attached ISA bus
To: None <firstname.lastname@example.org>
From: Niklas Hallqvist <email@example.com>
Date: 09/20/1994 20:48:54
>>>>> "Charles" == mycroft <firstname.lastname@example.org> writes:
Charles> Actually, the com probe sequence is a bit braindead. It
Charles> would be better to tickle the chip and see if it interrupts.
Charles> I'm not sure if there's a general way to do that without
Charles> outputting a byte, though. (Loopback mode doesn't work on
Charles> some clones.)
After speaking to several people I've got the conclusion that the ISA
bus *cannot* guarantee a 0xff value when reading an unexistant port.
Apparently, some busses keep a voltage in the middle of a logical zero
and one (for a fast switch time), some busses are pulled up, some are
pulled down. Do you have the 16450/550 specs? If we not do the tickle
probe, we might maybe go for a better kind of passive probe. Anyway,
is it so bad to output something during probe time? A break signal
maybe? I understand this is low priority, but maybe sometime...