Help guys...communication issue, I think?

[Demon]

Have you read this?

http://www.picbasic.co.uk/forum/showthread.php?t=17282

I was able to have a master PIC talk to multiple slave PICs at 115200. The trick is to have slaves enable usart transmit only when spoken to by the master.

I assigned each slave an ID (used in the data stream). The master would wait for a reply when necessary or keep on working.

A calling-all-slaves ID can be used to have them all do something, but they can't reply.

So no need for any comm IC, just straight PIC to PIC connections.

Robert

[kevlar129bp]

Hey Robert,

I actually did try that trick in my posted code above, but I just revisited it just to make sure and bummer...no love If you can take a glance at my code above and double check the technique I used, that would be awesome. Heck, maybe I'm not using it correctly?

Thanks again,
Chris

[Demon]

Check the code for slaves in this post:

http://www.picbasic.co.uk/forum/show...809#post116809

That's all I needed to do. Master TX to slave RXs, slave TXs to master RX, I think I had pull-ups at master.

I'm having a hard time with your code (sick, not feeling right).

I'd suggest making a copy of your program and strip everything except USART logic. Then post that stripped code if you have problems.

Keep it simple; talk to slave 1, wait for reply, talk to slave 2, wait for reply.

You can also use a MAX232 and listen in with your PC and see exactly what is sent. That helped me a lot.

Robert

[HenrikOlsson]

Chris,
You can't use Roberts aproach since you DO have the tranceiver chip in between the PIC and the bus. It doesn't matter if you turn of the USART TX in the PIC, the driver in the tranceiver chip will still be enabled and will still "hold" the line.

Since Robert does NOT have any tranceiver chip in between the PIC and the "bus" turning of the USART TX (ie making its pin high impendence) is effectively the same as what you need to do with your tranceiver chip (turning off the transmitter that is).

If your application invloves any sort of distances and/or deployement in the "real world" I'd definitely stick with some kind of bus like you have now. I wouldn't want to expose the PICs inputs/outputs directly to tens or hundreds of metres wires acting as antennas. Of course YMMV.

/Henrik.

[kevlar129bp]

Thanks guys,

I have succumbed to the fact of the board rework. Bummer for sure. 1 more question...I have looked at so many datasheets for transceivers that I have lost track. On some datasheets it shows the termination resistor on both the Tx and Rx endpoints, and on others it shows it only on the Rx endpoints? I suppose that was more of a statement rather than a question, but you guys get where I'm going with it... I've got my Rx endpoints terminated now...Am I good with that? Don't want to rework twice.

Thanks guys,
Chris

***Little deja vu here http://www.plcforum.it/f/topic/79753...422-multidrop/

[HenrikOlsson]

Hi Chris,
There's a section specifically covering bus termination in the .pdf linked to earlier, it covers the differences.

/Henrik.