Help guys...communication issue, I think?

[aratti]

Read this application note. It should help you to solve the problem.

http://www.analog.com/static/importe...tes/AN-960.pdf

Cheers

Al

[HenrikOlsson]

Hi,
Yeah, your tranceiver chips doesn't have a way to disable their drivers.
When two or more of those are connected to the same pair of wires they will fight each other. I think you want the MAX3080 - not 3081 - then take your TxLED signal and wire it to the DE-pin (HIGH to enable the driver) so that ONLY the board which is actually going to put data on the bus has its driver enabled, all other boards should have their drivers disabled.

/Henrik.

[kevlar129bp]

Hey Henrik,

Thanks for your reply. I looked at the Analog datasheet and the only thing that jumped out at me was their termination schema. My bus is built exactly like this one: http://datasheets.maximintegrated.co...80-MAX3089.pdf (page 20). Did I miss something in the datasheet, or is the 3081 only intended for point to point comms? If so, it sure sounds like a board rework is in order huh. bummer.

Thanks again,
Chris

[HenrikOlsson]

Hi Chris,

My bus is built exactly like this one: http://datasheets.maximintegrated.co...80-MAX3089.pdf (page 20)

Yes and no..... The actual bus may be built the same but your tranceiver chips (the MAX3081) doesn't have the DE-pin which you see in the schematic on that page and which you need for multidrop networks so yes, the MAX3081 is basically intended for point-to-point.

If the tranceiver has no way to turn of its driver then it will always drive the bus to one state or the other. Then, when another tranceivers driver is hooked across the same pair of wires and IT too tries to drive the bus to one state or the other there will be a conflict. One tries to drive it high while the other tries to drive it low - for example. On the chips with the DE-pin (Driver Enabled) you can disable the driver outputs all together.

/Henrik.

[kevlar129bp]

Thanks Henrik,

Bummer, I was afraid you were going to tell me that I wonder why the 887 board works with both boards on the bus though? That's the part that stumps me. Do you have any insight on that? Just seems that both of them would crash, not just one...

Chris

[Demon]

If you're stuck with those drivers, what if the PIC controls power to the drivers? Do they take time to "boot up"?

Robert

[HenrikOlsson]

Robert,
The chips are tranceivers...if you power them down they won't be able to receive either.
The PIC will never get any queries to send any data because the receiver is powered down, you might as well throw out the tranceiver all together... ;-)

Chris,
Can't say why it appears to work in some situations. Perhaps one driver is slightly "stronger" than the other (don't think so though).

/Henrik.