microcontroller max232
EIA/TIA- 232E and V.28 specification define the logic 0 is +5 up to 15V, and logic 1 is -5 up to -15V.
So, if applied to TTL (or came from) the logic level must be translated from 0.8V (TTL logic 0) to at least +5V (RS232 zero level) and 2.4V (TTL logic 1) to at least -5V (RS232 one's level).
The typical MAX 232 driver output voltage swing is ±8V and is guaranteed to meet these specifications(i.e ±5V minimum driver output levels under worst-case conditions). Input thresholds are both TTL and CMOS compatible.
In the opposite case, MAX 232 receiver translates voltage levels from +5V or higher (the RS 232 level for logic 0) to 0.8V or lower, and from -5V or lower to 2.4V or higher.
The MAX220–MAX249 family (line drivers/receivers)is intended for communications
interfaces, particularly applications where ±12V is
not available - especially in battery-powered systems. In addition, the MAX225,
MAX233, MAX235, and MAX245/MAX246/MAX247 use no external components.