>
> I am new to PICs so please excuse any stupidity.

No such thing here. Thi is a good project. It's on my task list of things to
do. I also want to add storage.

>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.

Personally I vote for 3: Use PICs that do not have UARTS. Distribute the load
by assigning only 1 software UART to each PIC. Use an 8 pin part like a
12C508. Use a clocked serial interface like I2C between the control PIC
like a 16F84. To maintain good clocking you'll probably want to generate
and distribute the 4 Mhz signal to the PIC/UARTS instead of using their
internal oscillators.

The good thing about this arrangement is that you can test with a single
JW part then duplicate the PIC/UARTS with OTP parts.

Thinking about it, I think that having an actual chip select may be useful
to fight the addressing problem of multiple chips. Also a interrupt or a
busy line may be helpful.

So there'd be a 4 wire connection from the control PIC to each PIC/UART. Three
lines CLOCK/DATA/INT are shared among all the PIC/UART and an individual
CS line for each PIC/UART. So a 18 pin PIC could easily drive up to 8
PIC/UARTS.

I just realized that I've used too many pins on the PIC12C508. Will have
to rethink.

BAJ