On Thu, Apr 08, 2004 at 04:43:10PM +1000, David Duffy wrote:
> Herbert Graf wrote:
>
> >I'm working on a project that requires converting unidirectional
> >data from one baudrate to another. If anyone has ideas on an elegant
> >and inexpensive way to do this, it would be appreciated.
> >
> >The converter is for a DMX transmitter. DMX is the standard protocol
> >used in the entertainment industry for controlling lighting equipment
> >such as dimmers, colour changers, fog machines, etc. It is electrically
> >RS-485, and the data is 250kbps.
> >
> >The crux is that I am interfacing it with an embedded PC using the
> >RS-232 port which runs at 115.2kbps. Of course there is a bottleneck,
> >but it's ok because the data being sent is generated less often then
> >what would be needed to max out the DMX output.
> >
> >Here are my current thoughts on a solution:
> >
> >- 2 PICs connected together with either parallel or I2C
> >- a PIC with 2 UARTs (but the only ones are 64TQFP, not nice to solder)
> >- a PIC controlling a 16550 UART
> >
> >
>
> It's not as simple as that. You have to generate the DMX other timing
> as well. eg. Break, MAB, etc. The DMX stream is not just a series of
> bytes @ 250KB. The timing is what syncs the receivers to the stream.
> David...

I have made a successful transmitter with a PIC that generates its
own data (from potentiometers) using the built-in USART. I simply turn
off the USART to generate the break, although some UARTs are apparently
capable of making breaks in hardware. A DMX protocol analyser though
thinks that my method is 100% fine with respect to timing.


Andrew

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