siemens mobile phones communication port voltage levels

[polarized]

Hi,


I am interested if the data in and data out pins on the siemens c35, c45 or mt50 mobile phones follow the ttl/cmos voltage levels or the above mentioned mobiles already have a voltage level translator inside of them capable of directly communicating with RS232 devices? If they do not have a voltage level translator like MAX232 can I assume that they are in fact UART capable and that I can directly connect them to an UART of a microcontroller without "glue logic"?


Bye.

 

[techie]

The C35 as far as I know has about 3.3V level RS232 on its pins. The polarity is reverse that of RS-232 and the same as on the pins of an 8051. So if you are using a 3.3V mirco, just connect directly. Otherwise, you have to use a level translator.

 

[polarized]

level translator for mobile phones

Hi,
If I use a level translator as you suggested I think that I have to place two of them because real RS232 levels are inverted, I mean the logical zero is from +5V to +12V and the logical one is from -5V to -12 V. What do you think can I use a simple resistor divider from the TX pin of a 5V microcontroller and in the other direction I dont use any glue logic but just connect the TX from the mobile to the RX of the microcontroller. I think that the logical "one" treshold of the 8051 for instance Atmel will correctly intepret the logical level? But, many data cables for mobile phones when communicating with PC-s just use a simple MAX232(5V operated) so what is the point of correctly matching the voltage levels if it works without the matching?


Regards.

 

[C-Man]

You do not need two rs232 converters because the max already inverts the signal (in sending and receiving edge).

If you use a microcontroller you can use a simple transistor as inverter in send and receive path.