Oops sorry, yes SPP as in Simple mode.=20

I am reading the data BEFORE I assert the busy signal, so the "bad host"
shouldn't affect me. And that timing diagram is pretty close to what I'm
doing. I think I need to re-visit my timing.=20

=20
-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Peter
Sent: 10 September 2010 18:13
To: piclist@mit.edu
Subject: Re: [PIC] PIC to PC Printer Port

 <jimf <at> webstudios.co.uk> writes:

> 	That's where i was heading, It is in basic EPP mode as the board
> inside the piece of kit is a 486/dx 33, (industrial equip) and the
> system boots from a floppy into Dos 6.2
>  I don't have control over the output rate, it is the rate that the
> dos app prints to the port at.
>  I am attempting to capture the output of the printer port and send
> it through my circuit. =20
>=20
> 	I have tried to match the specified timings on Ack/Busy as closely
> as possible, but occasionally i am losing bytes.=20

EPP mode? Not SPP? Anyway you should use a flipflop to assert NAK as soon a=
s
a
strobe pulse arrives and clear it when you are ready to receive more data.
Do
not make assumptions about the speed. A 486 will likely be able to push out
data
at a respectable rate, likely in excess of 500kHz. Any normal printer will
slow
that down at least 10 times so try to do likewise (wait >20 usec before
releasing BUSY and/or ACK). Also please see the comment "bad hosts may
invalidate data now?" in this link:

  http://www.theiling.de/parport/centronics.html

I.e. latch the data in hardware on the relevant edge of STB

-- Peter


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