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Date: Sat, 20 Apr 91 17:48:55 BST
From: Ian D Hawkins <idh@nabla.electrical-engineering.umist.ac.uk>
To: sci.electronics@ucbvax.Berkeley.EDU
Cc: idh@nabla.electrical-engineering.umist.ac.uk
Subject: I2C bus, 8051 compilers.
Message-Id: <9104201748.a004887@nabla.electrical-engineering.umist.ac.uk>
The Philips iic thing is indeed a wonderful low speed bus. The Philips
publication dealing with it is the 'Philips components technical
handbook no 4, 'Integrated circuits' part 12a. The formal bus spec
does make formidable reading, but the underlying operation is very
simple when you've got the idea. I've used the parallel port of
my atari st as a i2c interface with no alterations, if your computer
has an rs232 port with two outgoing modem control lines and one incoming
then you can, with some very simple level shifting circuitry, use
that as the interface. Multi master operation would not be possible, but
then for your likely uses you wont need it.
The software for the master transmiter/ receiver part is actually quite
easy to write. In Basic for example.
What I most like about the bus:
You can poll devices to see if they are there.
The chips are fairly cheap (2-3 pounds sterling typically for a battery
backed clock calender, or an 8bit i/o port , or a combined 4channel in,
1 analogue out a to d/ d to a converter).
You can bodge a working interface on almost any machine
You can put quite a few chips on the bus (at different addresses ,
16* 8bit dio, 8* a/d,d/a, several sram chips etc)
What I dislike:
The relative rarity of devices that support the protocol. If only
PMI or AD made some of their analogue interface chips with an I2C
compatable serial interface. I havent found a 12 (or more) bit d/a or a/d
converter, I have to glue these things in with 8bit dio chips. Ugly.
The relatively small capacitive loading that the bus lines are allowed
if they are to work at full speed (though not a problem with a slow
bodged interface).
And now a question. Is there an affordable 8051 high (ish) level compiler
available ( in C, Basic, (Fortran ?!), Forth ?), if you have used one,
would you recommend it ?.