Uart ttl rs232

Hello electro tech online

First of, I am using a Uc from cyrpess. I have been using the UART that I can pick in the designer program for the Uc. Then I have placed a MAX232 outside the Uc and then perfectly able to send info to the hyperteminal through my serial cable.

My project is, that I want to send info to an MP3 player I bought, that should be running RS232.

I am using this MP3 player https://www.electro-tech-online.com/custompdfs/2013/03/AU5121Sspec.pdf

I can make the Uc send info to my hyperterminal, but I cant make it work to the MP3 player. I do use the correct baudrate etc.

Quistion 1: Why does it say that my MP3 player use RS232 but also write RX (TTL), the TTL? In my understanding, it isnt the same. What should I be sending to the MP3 player?
Quistion 2: Do I need to have 2 UART's? I am not perfectly understanding the UART, RS232 and TTL stuff, even though I tried reading up on it.

In my Uc I choose the UART, program it etc. But also have to use the MAX232 UART outside the Uc. Do I need another UART again before the MP3 player?
Quistion 3: Do I even need a UART if my Uc send out as RS232 and the MP3 player receive RS232?

Im so confussdled!

When you connect the microcontroller UART to the mp3 player, you can't use the MAX232 interface chip. It converts the signal levels to the standard rs232 levels.. which are little strange. Negative voltages are logical one and positive voltages are logical zeros.

Signal levels from the microcontroller are usually called TTL level: 0 volts is logical zero and the operating voltage level (+5V) is logical one.

Just connect the microconntoller TX pin directly to the RX pin of the mp3 player (and RX to TX). The player seems to have series protection resistors on board so you can directly connect them. The mp3 player and the microcontroller need to share the same ground also.

misterT said:

When you connect the microcontroller UART to the mp3 player, you can't use the MAX232 interface chip. It converts the signal levels to the standard rs232 levels.. which are little strange. Negative voltages are logical one and positive voltages are logical zeros.

Signal levels from the microcontroller are usually called TTL level: 0 volts is logical zero and the operating voltage level (+5V) is logical one.

Just connect the microconntoller TX pin directly to the RX pin of the mp3 player (and RX to TX). The player seems to have series protection resistors on board so you can directly connect them. The mp3 player and the microcontroller need to share the same ground also.

Click to expand...

Thank you. Doesnt work yet, but getting closer I feel
Q1: So the reason why I need to use MAX232 when I connect to my serial port, is because it needs rs232 signals (not TTL) that is high positive and negative voltage?
Q2: So what happens, is that I use the UART inside the Uc to create TTL signals and then convert it with the MAX232 to rs232 signal's to be able to "speak" to my hyperterminal? And since a MAX232 is also referred to as a UART, I use 2 UART (one inside the processor)?

And then you want me to just connect the TTL signals from my Uc directly to the MP3 player which makes alot of sense.

Q3: The reason why RS232 is written on the MP3 player is then because that still is the name for that kinda signal? And that TTL only refers it to be at other voltage lvl's than the old RS232?

SimonTHK said:

Doesnt work yet, but getting closer I feel
Q1: So the reason why I need to use MAX232 when I connect to my serial port, is because it needs rs232 signals (not TTL) that is high positive and negative voltage?
Q2: So what happens, is that I use the UART inside the Uc to create TTL signals and then convert it with the MAX232 to rs232 signal's to be able to "speak" to my hyperterminal?

And then you want me to just connect the TTL signals from my Uc directly to the MP3 player which makes alot of sense.

Q3: The reason why RS232 is written on the MP3 player is then because that still is the name for that kinda signal? And that TTL only refers it to be at other voltage lvl's than the old RS232?

Click to expand...

A1&2: Yes, when you connect UART communication between microcontroller and your PC computer (hyperterminal) you need the MAX232 to change the signal voltage levels. If you connect UART between two microcontrollers you do not need the MAX232.

A3: The "problem" with rs232 standard is that it defines both the digital transmission and physical signal voltage levels.. so when somebody says "rs232 TTL" it means that the physical signal voltage levels are different from the standard rs232. I would prefer the term UART to be used with microcontroller rather than rs232.

misterT said:

A1&2: Yes, when you connect UART communication between microcontroller and your PC computer (hyperterminal) you need the MAX232 to change the signal voltage levels. If you connect UART between two microcontrollers you do not need the MAX232.

A3: The "problem" with rs232 standard is that it defines both the digital transmission and physical signal voltage levels.. so when somebody says "rs232 TTL" it means that the physical signal voltage levels are different from the standard rs232. I would prefer the term UART to be used with microcontroller rather than rs232.

Click to expand...

Ok ty very much. Then that is cleared out It still wont work but Im sure it will. Just need attention

"RS232 TTL" really doesn't exist because as what was said before, RS232 defines the signal levels as well. Way back when it was -3 to -25 and +3 to +25.

The key to remember is that "RS232 TTL" is inverted. You may also find that 1.8, 3.3 and 5v logic could be used, but typically it just means the voltage uses the TTL thresholds and inverted.

KeepItSimpleStupid said:

"RS232 TTL" really doesn't exist because as what was said before, RS232 defines the signal levels as well. Way back when it was -3 to -25 and +3 to +25.

The key to remember is that "RS232 TTL" is inverted. You may also find that 1.8, 3.3 and 5v logic could be used, but typically it just means the voltage uses the TTL thresholds and inverted.

Click to expand...

Ya it is really just to know the way around this. I figured out my Uc sends TTL signals and the MP3 player receive TTL signals. This is all I needed, just directly connect TTL to TTL without any MAX232.
The problem for me was, that I was using a premade Uc circuitboard from cypress, that had UART written inside the developer program and I was reading that the UART did send TTL signals. But they had also placed a max232 on the circuitboard. I ofc used the signals behind the max232 (that some people also call UART, which just make stuff more confusing) instead of directly from the Uc.

Just wanted to end this thread, since it now works.