> The 9th bit is an address/data bit. When set it indicates an address that
> the packet it targeted for. Reset indicates data.
>
> The usefulness on the PIC is that that its USART can be configured to
generate
> an interrupt only if an address is sent. So the basic gameplan when you
have
> multiple nodes on the line:
>
> - Everyone sets up to just accept addresses.
> - When an address is sent everyone is interrupted and checks the address.
If the
>   address doesn't match, when go back to accepting addresses only.
> - However if the address does match configure the USART to accept data.
>
> So once a matching address is sent, only the targeted station will receive
the
> data. All the other stations will ignore the line until another address is
> sent.

I think that is one of the things that can be done with it. I am simply
using the 9th
bit as a single address bit - if it is set, the "main" 8 bits are for one
PIC, and if the
9th bit is clear the data is for the other PIC.

> This issue comes up time to time on the list. Personally I always thought
the
> best tack was to attach the PC to a PIC which does 9 bits to the rest of
the
> network and uses a 8 bit software UART to talk to the PC. By the time you
> finish contorting your Windows code to mangle the PC UART to simulate 9
bit
> mode, you will have pulled all your hair out of your head.

I thought of that, but I don't have a spare 873 here.

> Since your final target is 2 PICs anyway, why waste time trying to get a
PC
> to simulate?

The PIC that the PC is simulating a PIC which interfaces to a Microsoft
digital joystick. I was having problems with that and wanted to put it on
the back burner and work on the other (receive) side of the link and have a
way to test out the serial input. The main reason I did it is to learn more
about programming a Windows GUI program in C, instead of just the console
stuff I do at school.

Andy


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