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why max232 is needed

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Nirav Barvadia

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Sir,
I have project of starter of 3 phase electrical motor starts on and off through miscalls,
This project must have to use sim300, max232, and micro controller.
What is and why should max232 is needed to interconnect sim300 and 8051?
And what is pin to pin connection between sm300, max232 and 8051?
 

If your SIM300 modem has TTL interface then you can cross connect it to uC UART pins. If your SIM300 doesn't has TTL interface but has RS232 interface then you need AX232 between uC and SIM300 modem. TTL works at 5V and RS232 works at 12V. If distance between uC and SIM300 is more than TTL cannot be used and you need RS232. If distance is not more than 15 cm and SIM300 has TTL interface pins then you can use it directly to connect uC UART pins.
 

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this complete project between 8051 and GSM will help you

**broken link removed**
 

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I get it, thanx
And what is the pin to pin connection between Sim300 max232, and8051
 

Most of the Microcontrller has UART communication, the serail communication Output of the micro-controller is form of TTL (Transistor Transistor Logic) which means that the TTL levels (Digitally 0's and 1's) are as ,High - 5v -3.3v and Low -0volts.
But in standard serial port (RS232) logic high (1) is represented by a negative voltage – anywhere from -3 to -25V – while a logic low (0) transmits a positive voltage that can be anywhere from +3 to +25V. On most PCs these signals swing from -13 to +13V.

So there are a voltage different s in between serial communication of Standard RS232 and Microcontroler .this problem is solved by the max232 ic .
 
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