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From: "John Jardine"
Subject: Re: Parallel port speed
Date: Tue, 21 Jan 2003 15:30:00 -0000
NNTP-Posting-Date: 21 Jan 2003 15:15:34 GMT
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Dave wrote in message
> Does anyone know the speed (rate) at which a single pin of the parallel
> can output data? The port can be set to standard or EPP, whichever is the
> fastest. I can't seem to find trustable numbers.
You will not be able to get much beyond 100k bits (or bytes) per second from
the port, even if you code the "in"s and "out"s as a tight machine code
Every data 'out' and 'in' command is dragged out by upto 5uS of ISA bus
synchronisation delay. So this establishes an upper speed limit and applies
to all PC's.
for example (in Basic) ...
Lpti=888 'usual hardware address (in decimal)
out lpti,1 'put a logic high on data pin(0), (actually lpt1 pin2)
out lpt1,0 'put a logic low on data pin(0)
On a 33meg '486 this bare bones loop runs about 5MHz. As soon as the Lpt1
hardware is involved the speed drops to 100kHz.
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