Want to receive data in microcontroller

[Hayee]

Hi Guys
I have a scenario in which two devices are connected with rs232 protocol. Device 1 asks for some data and device 2 provides the data to device 1.
Now what I want to do is to add a microcontroller which also send command to Device 2 to get some data. Here I attached the image which shows the scenario.
Device 1 asks for data at a defined interval so my microcontroller will ask for data from Device 2 at a pre-time interval.
My question is Can I do something like that as shown in the picture by placing Diode at Tx side of Both Device 1 and Microcontroller?
Maybe it looks so simple but actually this cannot be achieved.
Required suggestions from your side.

Thanks and best regards

 

[Hayee]

Guidance required guys.

 

[KlausST]

Hi,

in my post#3 I wrongly had the TTL levels in mind. (as already mentioned)

If you want clarificaton, do it the objective way: use one of the free simulation tools.

Klaus

 

[Hayee]

Hi,

in my post#3 I wrongly had the TTL levels in mind. (as already mentioned)

If you want clarificaton, do it the objective way: use one of the free simulation tools.

Klaus

It means post #14. I can implement this

 

[KlausST]

Hi,

I´ve alredy replied to your post#14. Did you read it?
Test the schematic of post#14 ... then also with reversed diodes to see which one is correct.

Klaus

 

[Hayee]

KlausST I will definitely use some simulator and test the results and post it here.
Another scheme coming in my mind, If I convert the logic level of Device1 to TTL and then use Diodes like in the picture and then convert again to MAX232 Level. Will this be OK?

Kindly guide me in this scenario

 

[FvM]

Pull-down resistor common anode to VS- missing,

 

[KlausST]

Hi,

good idea.

But again I doubt that the diode direction is correct.

Truth table of what you need:
(UART is idle HIGH)
A = data coming from device1
B = data coming from microcontroller
Y = data going to device2

 A  B | Y ; Info
 ---------------
 L  L | L ; both are trying to transmit = data collision. Try to avoid this situation
 L  H | L ; A transmits, B is idle
 H  L | L ; A is idle, B transmits
 H  H | H ; A is idle, B is idle

This is an AND logic.
Instead of 2 diodes and a pull up, I´d use single gate logic, like 74HC1G08

Klaus

added:
The disadvantage (compard to post#1) is, that now the "microcontroller" is an essential part.
+ in post#1: when the microcontroller is not powered up or not connected, then device1 and device2 can communicate.

- in post#25: when the microcontroller is not powered up or not connected, then device1 and device2 can not communicate.