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Subject: Re: External Serial LCD Display / Keypad
From: Andy Finney (andyfinney_at_yahoo.co.uk)
Date: 2004-08-08


sophona wrote:

> you will have to open your archos and do the serial mod. then you'll
> have full duplex serial lines. (ttl level)
> The pins are quite accessible and you can get them out easily through
> the line in connector (if you have a studio)
>
> If you don't want to open it you'll need a micro controller.
> Or if you don't want to use the keypad, you might be able to transmit
> only with the remote pin.

I have been doing a bit more investigation and I think that I can possibly
get away without doing the serial mod - my serial display simply accepts
commands for the screen (presumably with no response sent back). It also
allows buffering of key-presses for remote-polling. Key presses can be
stored until requested for.

I guess it would be quite simple for me to implement a "protocol" (in the
loosest sense of the word) by sending the information then polling for
key-presses alternately.

Anyway back to it - my questions are: -

1. How easy will it be to implement this under rockbox - I am not scared of
getting my hands dirty with C, but interrupts and low level stuff may take
me a bit longer to understand. Are there any examples anywhere - e.g.
switching the pin to trx/rx etc....

2. Has anybody got any ideas on a suitable circuit? I am going to have to
use RS232 voltages instead of TTL (it turns out my LCD doesn't support
modding for TTL). I guess I am going to have to build the RS232 level
converter, but with some modifications to allow bi-directional comms on the
remote pin. I am stumped for this. I have not found anything on the mailing
list - has anybody got any links/ideas that will point me in the right
direction?

Thanks,

Andy.

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