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Subject: Re: External Serial LCD Display / Keypad
From: sophana (jobarjo78_at_yahoo.fr)
Date: 2004-08-09


Andy Finney wrote:

>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.
>
>
hmm, not so easy for me to poll something. maybe a thread could do it
and write in the button queue.

>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....
>
>
>
There is a software tx patch for transmiting over the remote pin. It is
quite simple to use.
I already something like what you want except that my external display
is a sony car radio head unit.
If you want you can look at what I did on
http://sophana.free.fr/unilink.html

If you use the full duplex, read the sh1 data sheet. It is not very hard
to use the UART for transmitting.

>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?
>
>
>
If you use the remote controller pin, don't forget that the device will
have echo when it will talk. Verify that it won't be a problem.
Generally, RS232 input voltage levels are ttl compatible except that
they are inverted.
you will have to use an open collector NPN transistor for the RX, and
again an inverter for the tx.

>Thanks,
>
>Andy.
>
>_______________________________________________
>http://cool.haxx.se/mailman/listinfo/rockbox
>
>
>

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