Connecting two PDAs to Cambridge 302 out (Tx)

[Andrzej Kobus]

I hope someone here will be able to help.

Can one safely connect two devices that would read (Rx) from Cambridge
302 (Tx)?

I have a signal right now going to ClearNav only but I would like to
split the Cambridge out signal (Tx) so I can also receive the data in
a backup PDA. The second device would only receive the data from
Cambridge not send anything.

I found some references that suggest this is commonly done with RS232
interfaces, but I am a bit suspicious since connecting 2 devices would
reduce resistance of the load. The manual says two PDAs are not
supported but it is difficult to say if this is dictated by circuit
issues or by protocol being messed up by two PDAs trying to
communicate bi-bidirectionally at the same time. Again, I only want to
receive.

Any knowledgeable reply would be appreciated.

It is also interesting to see PowerFlarm specifying that only one
external device could be connected to the DB9 serial port. I would
like to understand that as well. What is the reason for this, hardware
or software?

[Peter Purdie[_3_]]

As many devices as you like can receive 302 serial data out (at least three
anyway in my experience).

Obvously you know Andrezej, only one can transmit to the 302 and switching
is needed if you want bi-directional communication (for example, task
exchange).

The 302 serial DB-9 connector also has separate power out on pins 6 and 9
to power 2 PDAs.



At 21:41 30 September 2012, Andrzej Kobus wrote:
>I hope someone here will be able to help.
>
>Can one safely connect two devices that would read (Rx) from Cambridge
>302 (Tx)?
>
>I have a signal right now going to ClearNav only but I would like to
>split the Cambridge out signal (Tx) so I can also receive the data in
>a backup PDA. The second device would only receive the data from
>Cambridge not send anything.
>
>I found some references that suggest this is commonly done with RS232
>interfaces, but I am a bit suspicious since connecting 2 devices would
>reduce resistance of the load. The manual says two PDAs are not
>supported but it is difficult to say if this is dictated by circuit
>issues or by protocol being messed up by two PDAs trying to
>communicate bi-bidirectionally at the same time. Again, I only want to
>receive.
>
>Any knowledgeable reply would be appreciated.
>
>It is also interesting to see PowerFlarm specifying that only one
>external device could be connected to the DB9 serial port. I would
>like to understand that as well. What is the reason for this, hardware
>or software?
>

[Andrzej Kobus]

Thank you for the replies!