Hi we have seen introduction about serial communication and about MAX232 chip in my previous post. Let us now see at the three main sections of MAX232
- Dual charge pump voltage converter – this section uses two external capacitors. One is used to double the +5V input to +10V and the other is used to invert +10V to -10V.
- Transmitter section – each of the two transmitters is a CMOS inverter powered by +10V internally generated supply. The input is TTL and CMOS compatible with a logic threshold of about 26% of VCC. The input of an unused transmitter section can be left unconnected. An internal 400k ohm pull up resistor connected between the transistor input and VCC will pull the input high forming the unused transistor output low.
- Receiver section – the two receivers fully conform to RS232 specifications. Their input impedance is between 3k ohm either with or without 5V power applied and their switching threshold is within the +3V of RS232 specification. To ensure compatibility with either RS232 input or TTL/CMOS input, the MAX232 receivers have VIL of 0.8V and VIH of 2.4V.