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PICList Thread
'I2C Master Mode Question'
1995\08\19@141648 by Andrew Warren

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Greg Solberg <spam_OUTgregTakeThisOuTspamMIGSOL.COM> wrote:

>I'm implementing an I2C interface to an 24LC01 EEPROM.  I had, of
>course, planned to use the built in I2C ports of the '73.  After
>reading the data sheet and a few Microchip App. notes, it seems that
>all the fancy I2C hardware in the '73 is only usefull for slave mode.
>As far as I can tell, I have to push all the bits out in software, and
>I gain nothing by using the I2C ports over any other port for Master
>Mode.
>
>Is this true or am I missing something?

Greg:

It's true... The Microchip databook boasts of "support in hardware to
facilitate software implementations of the master functions", but for
single-master mode, this so-called "support" amounts to nothing more
than forcing two bits in the PORTB output latch low.  This saves a
whopping two BCF instructions, but requires an extra pullup resistor...
Not exactly a fair trade.

It this point, I'm tempted to ask the following question:

   Given that Microchip wants to become a leading supplier of I2C
   EEPROMs, doesn't the lack of hardware support for communication
   between those EEPROMs and Microchip's only other products (the PIC
   microcontrollers) seem sort of stupid?

However, I'll refrain... My local FAE is busy enough without having to
field angry phone calls from Microchip's list-monitors.

-Andy

--
Andrew Warren - .....fastfwdKILLspamspam@spam@ix.netcom.com
Fast Forward Engineering, Vista, California

1995\08\20@162356 by Brian Read

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It's true, the I2C stuff built into the PIC's is
ABSOLUTLY worthless for master mode operation. I think
that this was a real error on MCHIP's part and have never
heard an explanation of why they did it this way.

Happy bit banging,
Brian

1995\08\21@045419 by Adrian Godwin

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> It's true, the I2C stuff built into the PIC's is
> ABSOLUTLY worthless for master mode operation. I think
> that this was a real error on MCHIP's part and have never
> heard an explanation of why they did it this way.
>

Might it be related to Philip's copyrights on I2C ?  They used to insist
(perhaps they still do) that any use of the I2C protocol required that
at least one device manufactured under a licensing agreement with
Philips should be used on the bus.

I seem to remember that Microchip had a disagreement regarding their
I2C EEPROMS - if/when it was resolved, perhaps Philips insisted that
Microchip keep away from hardware I2C master implementations ?


Going a bit off-topic, is there any news of a PIC with USB ? The USB
web page seems to indicate that some microcontroller manufacturers are
likely to offer on-chip USB interfaces, and PICs are popular in the
desktop peripheral market so it seems likely that Microchip would
want to be in on it.

Anybody got views on the likelyhood of USB's success ?


-adrian

ps .. for anyone who hasn't seen the hype, USB is a microsoft/intel
supported serial bus for use on desktops .. mice, printers, modems, VR
peripherals etc. It's single-master, 12Mb/s, multiple star topology.
Further details (including a technical spec) at http://www.teleport.com/~usb/.

1995\08\22@151813 by Christer Johansson

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Hi,

>Going a bit off-topic, is there any news of a PIC with USB ? The USB
>web page seems to indicate that some microcontroller manufacturers are
>likely to offer on-chip USB interfaces, and PICs are popular in the
>desktop peripheral market so it seems likely that Microchip would
>want to be in on it.

I would like to hear more about this MCU if it exists or are in the
developing state. If anyone (Microchip ?) have any information please
let us know...

>Anybody got views on the likelyhood of USB's success ?

I had high hopes for the ACCESS.bus but if USB is what they say it
is I think USB is the thing. But in the end everything in this business
depends how well we users adopt it (IMHO).

PS...It isn't off-topic *IF* there going to be a PIC with USB ;-)

/Christer

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1995\08\27@212217 by Kevin R. Jones

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Does anyone know where to find the specs on the I2C protocol ? With all
the discussion going on about it, I'd like to find out more info on it.

Kevin Jones

1995\08\28@041300 by Markus Seim

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Kevin Jones wrotes:

> Does anyone know where to find the specs on the I2C protocol ? ...


Philips has published an I2C-bus specification:

       'The I2C-bus and how to use it (including specifications)'

The latest version of this spec. is from january 1992 (I think so).
You can get it from any Philips Semiconductors representation or direct
from Philips, 6500 MD Eindhoven, The Netherlands.

Maybe someone knows a WWW site where this spec. is published ?

So long, Markus
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                      <Y
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1995\08\28@080452 by Werner Terreblanche

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>
> Philips has published an I2C-bus specification:
>
>         'The I2C-bus and how to use it (including specifications)'
>
> The latest version of this spec. is from january 1992 (I think so).
> You can get it from any Philips Semiconductors representation or direct
> from Philips, 6500 MD Eindhoven, The Netherlands.
>
> Maybe someone knows a WWW site where this spec. is published ?
>

Well I don't know about that, but how 'bout referrring to the I2CFAQ?
It's a nice long document containing all the relevant info one might
require.  The maintainer is called Vincent Himpre. He can be
contacted at:

  By e-mail :   Internet  : EraseMEVincent.himpespam_OUTspamTakeThisOuTping.be  (preferred)
                            vi_himpespamspam_OUTmietec.be
                Fido      : 2:291/1912.8

  By Snail-Mail :   Vincent Himpe
                    A.De Taeyelaan 12
                    8792 Desselgem
                    Belgium

  This FAQ will be posted to the following newsgroups:
        comp.protocols.misc
        sci.electronics








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---------- Technology is Great...  when it works! ---------------

1995\08\28@082600 by David Warman

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In message <spamBeGone199508281206.NAA26466spamBeGonespamlistserv.rl.ac.uk>, TakeThisOuTwterrebEraseMEspamspam_OUTplessey.co.za wri
tes:
>   This FAQ will be posted to the following newsgroups:
>         comp.protocols.misc
>         sci.electronics

It's expired at my site (or at least I can't find it in these groups!)
rtfm.mit.edu doesn't seem to have it either.  Anyone found an archive
with a copy?

Thanks,

Dave.

1995\08\30@084544 by Christer Johansson

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Hi Kevin,

>Does anyone know where to find the specs on the I2C protocol ? With all
>the discussion going on about it, I'd like to find out more info on it.

Try to get hold of the following data books from your local Philips
distributor, they have lots of information....

IC2a - I2C-bus compatible ICs [# 9398 165 50011]
IC2b - I2C-bus compatible ICs [# 9398 161 30011]

/Christer

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