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Will the TTL pins on this GSM module be connected directly to AT89C51 microcontroller? Answered

I plan on using this GSM module with an AT89C51 microcontroller and was wondering whether I needed an extra MAX232 chip since the module has Rx and Tx jumpers broken out. Are they TTL? Could they be directly interfaced with the microcontroller? I have circled the pins in question in the picture. 

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verence

3 years ago

RTFM or measure the voltage on the TX pin. Close to 0V/5V = TTL, something <0V, >5V = RS232 levels or near by, use an MAX232 or another level shifter.

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r5sbverence

Answer 3 years ago

Hey, I tested this with a CP2102 board by connecting the Tx and Rx of each board and the serial comm works! So no need for an extra Max232 in this case.

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steveastrouk

3 years ago

Looking at it from here, there's a MAX202 on the back (better than the MAX232, smaller caps), so the output is likely to be bipolar RS232. If you want to make it different, then take the 202 chip off, or hack the input/output of the 202 and connect to the 89C51.

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r5sbsteveastrouk

Answer 3 years ago

Sorry for the late reply! I've tested the module with a CP2102 module and turns out those Rx,Tx pins circled output TTL directly, so no need for an extra MAX232 converter board! :D

Thanks.