Multiple PICs on usart network

[dhouston]

The MAX3322E & MAX3323E are designed for this, as well, if using an RS232 transceiver.
http://www.maximintegrated.com/datas...ce=supplyFrame

[JoseJimenez]

Hi,
I am assembling this circuit. 1 Week ago i am suffering of the same situation that you have.
I am conecting 5 PIC 16F690, 1 as master (Tx conected to 4 Rx) and 4 slaves (all tx in parallel with other slaves...)

If I only conected 2 pics (P2P) all works fine, but adding 1 more, the Tx from 1 slave to master is corrupted.

I have the solution, can you reply what did you do to solve?


/jose p

[JoseJimenez]

this is my mail:
[email protected]

[Demon]

Hi,
...can you reply what did you do to solve?

I have only 1 slave enable the TX line at one time:
http://www.picbasic.co.uk/forum/show...809#post116809

Robert

[sayzer]

1. Two Schottky diodes on TX lines could be one solution. This way, one TX line does not effect the other.

or if not using diodes,

2. After each Transmit, you may disable USART and make TX pin input pin. When you need to send again, make TX pin an output pin and enable USART, then transmit.
If one TX line is an input pin, it will not effect the network during the transmission of other TX line.

These two are only suggestions and are not tested.

[Demon]

Can't comment on the diodes, but disabling USART also turns off receive. That's why I disabled only transmit.

[dhouston]

The URL I referenced in post #4 shows diodes in TX lines. There's no coding required. Schottky diodes would be best.
http://cool-emerald.com/?p=711

[JoseJimenez]

Mr Demon,


I definitely solve this.
You will need a couple of transistor per each Tx output and 3 resistor.


As you said, if you disable the usart, also Rx line will be disable.
If you use diodes, you will need a conversor as MAX 232...
Problem with diodos, is due to signal keep positive if Tx is idle. Plus this, Impedance for Tx and Rx line are so sensitive.


If want to communicate several PIC without using interfacing, you can do it using the schematic that I will post next.


/jose p.

[Demon]

The URL I referenced in post #4 shows diodes in TX lines. There's no coding required. Schottky diodes would be best.
http://cool-emerald.com/?p=711

How fast a baud rate do you think this can handle?