piclist 1999\02\09\112802a >
Thread: PICs, I2C and Front panels.
face BY : keithhRemoveME@KILLspamarcam.co.uk

> I want to have a central micro running as a "supervisor"
> and a second micro implementing a remote keypad and LCD display.

> I was looking towards I2C, but because of the remote micro's
> limited use, the low-end PICs do not implement I2C in hardware
> (so a software solution would be necessary).
> Does anyone have experience with this type of application?

Yes, our flagship amplifier the Arcam Alpha 10 has a Holtek
on the main board, allowing it to run as a simple power amp.
If connected to a pre-amp board and a front panel containing
the PIC16C65 I programmed, the PIC takes over the show and
runs the application (being an integrated amp).

They talk via I2C, in multimaster mode.

> Could you give me some advice/battle scars?
> What is the "best" way to interface the two?

Forget software slavery. It may be possible, but
doing it with the SSP hardware is work enough!

The simplest way is to have one being the master
and one being an I2C slave. One of them has to be
the slave, and that one should have I2C hardware.

Which is the simpler micro?
What is the non-display micro doing?

I think the wiser choice may be to make the display
micro the slave, with an attention request signal
to say "Something's changed, come check it out".

My PIC normally runs the show, but expansion boards
(e.g. home cinema) can enslave it so that it acts
as a dumb terminal. It can then either transmit
commands describing user events, or use an
attention request line as described above.

I've wired my front panel to my PC printer port
and had the PC hosting an application:
press buttons or twiddle the knob, the PIC
alerts the PC which reads it, then the PC sends I2C
messages to the PIC which put data into the
volume control chips, multiplexers, LEDs and
flourescent display.

The latter is compatible with the HD44780 chip
used in LCDs.


<36C0627C.7CBD@arcam.co.uk> 7bit

See also: www.piclist.com/techref/i2cs.htm?key=i2c
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