I connect my MCU (3.3 V) to an RS232 device. I got the right output voltage on each side. And there is communication between them. But I did not get the right answer from the RS232 device. Is the board broken?
The code works well with a previous self-made max3232 board with the maxim max3232 Do I need to add a resistor to the pins T1IN and T2IN on the board? Since we have the resistors on the self-made board
Hello yaoz.
There should be everything on the board it needs to function and it only requires power and connection to your system. Can you provide some photos and a schematic showing how you have the board connected? Maybe we can spot the issue from those.
Hi TS-Chris,
The board is connected exactly as the hookup-diagram from the product side.
I used an oscilloscope to read the signals on RX and TX. What weird is that the oscilloscope shows the correct answer (on the pin R2OUT) from the RS-232 device. But the MC shows a totally different value for the same signal. I am sure that there is no problem with the MC and the program since they work well with our self-made board.
Do you have any ideas about the reason? Thank you.
We don’t have a hookup diagram for this product so I’m unable to understand what your setup looks like.
There is a possibility you have a bad board, but I’m unable to determine that from the information given. Can you please provide some photos and/or a schematic showing how you have the board connected to your devices?
Here’s a high level overview of how signals flow through the board:
Here’s an example of how you would connect the board to a RS-232 and TTL circuit:
The problem is solved. I added a pull-up resistor to the pin TIN, as the following schematic shows. And it works now.
[attachment=2]BOB-11189 hookup-revised.jpg[/attachment]
I would be nice if you can provide a new version with pull-up resistors in the future. Maybe the current board works with Arduino, but it does not work with my MC (Infineon XMC4500). And our self-made board (with the pull-up resistor) also worked well with Arduino.
For someone who may know the reason why it does not work without the pull-up resistor, I will explain my previous hookup and investigations in following.
The board is connected previously as follows:
[attachment=0]BOB-11189 hookup.jpg[/attachment]
However, it does not work with my MC. I read the TTL OUT signal from an oscilloscope. I was the desired answer (e.g. 0x4F) from the RS-232 device. But the interpreting from the MC is different (it turns to be 0x46 or some other values).
Then I made another test to connect the RS232 Out to RS232IN:
[attachment=1]BOB-11189 hookup - invest.jpg[/attachment]
And the MC can receive exactly the same signal as the one it sends out.
I have no idea how does it happen. Maybe you can give an explanation.
I’m glad the resistor fixed the issue for you. We have not had to use a resistor to get these to work and have never had a customer state they do too so I’m not sure what could be causing that issue for you.
