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'[OT] Easiest I2C PC Master)?'
1999\04\26@190910 by Richard Martin

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I also implemented a PC to I2C interface some time ago,
using direct connection to PC parallel port. This was pre-
integrated motherboard (i.e. zap your parallel port and
you buy another $10 ISA card, NOT another Pentium whizzy).
Also under DOS and before PCI-bridges (don't EVER go
there if you don't have to!!). Hint: Even (almost) on
modern PCI-bridge systems, the ISA-bus spec 'requires'
that an OUT/IN instruction be 500 nsec., so on fast machines
8 sequential/identical OUT/IN instructions take almost exactly
4.0 usec. INDEPENDENT of cpu clock (ignoring interupts) so you
can get I2C type timing (under DOS, not "DOS-box") for free.

The original PC parallel port used 7407 O.C. drivers with
4.7k pullups., almost right on, for status signals..

I got it to 'work' well enough to observe as O.K. on 'scope, but
dropped it shortly after.

Another hint: the RB.6 and RB.7 pins on EPIC-like P.C.
parallel port PIC programmers, can be programmed to be I2C
signals (IF you can avoid the WinDoze <or worse NT->
interface problems). And it won't eat your motherboard.


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