How about analogue or digital multiplexers controlled by a PIC? (Plus output
buffers etc as required)

Richard

> -----Original Message-----
> From: Thomas Brandon [mailto:tom@PSY.UNSW.EDU.AU]
> Sent: Friday, June 04, 1999 12:54 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: 2-way MIDI
>
>
> I am new to PICs so please excuse any stupidity. I would like
> to design a
> MIDI "router". It would have say for INs and OUTs and allow
> you to route
> messages between the various channels on the INs and OUTs
> (e.g. route IN1
> Channel 3 to OUT1 Channel 4 and OUT2 Channel 5). I realise it
> is a fairly
> ambitious project to start with but I don't expect it to be
> easy or fast.
>
> At the moment I'm trying to devise a way of supporting that
> many MIDI ports
> (i.e. 8). I can think of two possible methods:
> 1) Use PICs such as the 16C74 that have USARTs.
>     One disadvantage of this is that no PIC has more than 2
> USARTs thus for
> a 4x4 box I would need at least 4 PICs (probably 5, 1 to deal
> with moving
> messages between the other 4 PICs). Also, I'd need a fair few
> JW parts for
> prototyping and these don't come cheap (especially here in
> Australia). In
> this arrangement I guess I2C would be a good way of
> communication between
> PICs.
>
> 2) Use external UARTs
>     I am unsure of how this would work. How many UARTs can
> you "drive" off
> one PIC? How many I/Os do you need for an external UART? I gather an
> external UART can be used asynchronously by using the
> external interrupts on
> PORTB. So, I guess you're limited to 4 UARTs on one PIC.
>
> Another possible problem is that MIDI runs at 31250 baud so
> the UART must
> support this. I know the PIC USART can and I've heard SMC
> UARTs support
> 31250 out of the box( so to speak). I gather you can change
> the crystal on a
> UART to get other rates but is 31250 easy to do with
> available crystals? BTW
> the MIDI specs allow for a +/-1% on the speed so there a bit
> of room in
> which to use.
>
> In summary my basic questions are:
>     - Do either of these designs appear even slighly feasible?
>     - Is there a better design?
>     - Is interfacing a UART to a PIC
> possible/difficult/processor intensive?
>     - Is it possible to do 31250 on all UARTs? (Easily?)
>
> Sorry for the large ammount of info but I'm not sure what
> is/isn't relevant
> yet.
>
> Thanks in advance,
> Thomas Brandon.
>