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I need to comunicate serial with 3 devices:

Assuming those devices talk back to the mcu (they are write-only devices), the trick is to use a resistor + mcu pin to isolate them from the bus: from the serial bus, run a resistor (1k) to the device. On the device's serial pin, connect a small resistor (110ohm or less) to a mcu pin (UART_ENx pin). Default the UART_ENx pin to set / output.

When you want to talk to this device, tri-state its UART_ENx pin; at the end of the transmission, turn it as output.

This approach allows you to connect as many write-only uart devices to one hardware uart.
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The manufacturer replied that I will need to communicate without using the RS232 cable provided.
He gave the pin assignment that I had attached here.

My doubt now is if I can only use RX and TX pins do read the serial data.
I will keep searching and trying.


* decoder interface pinout.jpg (8.67 KB, 400x300 - viewed 11 times.)
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Finally solved the problem using a RS232 to TTL converter board and a null modem.

Null modem was need just because both connectors are female, scanner and converter.

Thank you all.
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Finally solved the problem using a RS232 to TTL converter board and a null modem.

Null modem was need just because both connectors are female, scanner and converter.

Thank you all.

Well a male to male null modem connector does more then just allow two female connectors to be attached to each other, as a null modem also crosses the send and receive signals and cross connects a few of the RS-232 control signals between the two connectors. There are straight-through gender changers that can connect two female connectors without changing any of the wiring paths and are simple called gender changers. a null model connector performs wiring modification and are avalible in male to male, female to female, or male to female configurations.

So if your set up works using the null model connector you selected then it was not just because you had two female connectors needing attachment to each other but rather also a change from DTE to DCE identity for one end of the two connections. A DTE serial device cannot direct wire to another DTE device as neither can a DCE wire directly to another DCE device, they must be of opposite identities.

Lefty
« Last Edit: March 02, 2013, 09:20:17 am by retrolefty » Logged

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You are so correct retrolefty,

in fact I have not yet a null modem.
I have bought a gender changer thinking it would solve my problem, but not.
So I removed it, and used simple wires crossing tx and rx like a null modem between the RS232 to TTl converter and the serial cable from the barcode scanner.
It worked perfectly wired this way, so I expect it to work with the null modem (that I will buy soon).

Thanks for your comment.
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