decarus WROTE:does it means i'll need two max232. 1 is 5 V powered that converts RS232 to TTL then the other max232 to lower the voltage to 3.3 with Vcc = 3V.
No, you need to get clear with the operating voltage, not the logic interface voltage. If the MAX232 cannot operate, it mean it is useless. Thus, how can it convert voltage?
The function of MAX232 is to convert RS232 signal to TTL logic signal (0-5V), that is why sometime we call MAX232 as RS232 level shifter. But since the specification of normal MAX232 require 5V or >3.3V to operate, you need to find other type of RS232 level shifter.
You need to get a RS232 that operate with 3.3V, for example MAX3225, MAX3232CDR and more.
Finally, this might be one of the reasons the circuit does not work, do check all the voltage across your circuit to ensure the connectivity is correct.