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From: dano@ssc-vax.UUCP (Dan Olson)
Newsgroups: comp.sys.amiga.hardware
Subject: Using the Parallel Port
Keywords: ppppppppport
Message-ID: <3257@ssc-vax.UUCP>
Date: 17 Mar 90 17:06:40 GMT
Organization: Boeing Aerospace & Electronics, Seattle WA
Lines: 30

Some questions regarding the parallel port on the Amiga and the 8520
chip.  I am building a device that needs to be written to and read
from.

1)  Is there anyway for a device on the parallel port to know
whether it is being written to or read from with only a read or
write to the 8520 port B?  According to my old hardware docs, it
says that data ready (PC pin) will be brought low on any port B
access, so how can I tell if it's a read or write?

2)  When acknowledge (FLAG pin) is pulsed, is it only used for 
generating an interrupt, or will it also cause port B to latch 
what's on its pins?

3)  If the port B is driving the parallel port data lines, is it a
no no for a device on the port to pull any of these data lines to
ground? (Writing to the parallel port when the device connected to
it has data on the pins).

For maximum compatability with AmigaOS I'd like to use the
parallel.device for accessing my device.  Any insight on how it
handles the parallel port would be appreciated.  I assume it reads
or writes new bytes on acknowledge interrupts.  How fast can the
parallel.device respond to an interrupt?

Thanks for any help.


-- 
Dan Olson  (UUCP ..!uw-beaver!ssc-vax!dano)