MAX232 chip is a single-supply level-shifting chip designed by MAXIM for the RS-232 standard serial port and operates from a single +5V supply.
The device is particularly well-suited for battery-powered systems because its low-power shutdown mode reduces power consumption to less than 5uW. The MAX225, MAX233, MAX235, and MAX245/MAX246/MAX247 require no external components and are recommended for applications with limited printed circuit board space. The MAX220–MAX249 family of line drivers/receivers are designed for EIA/TIA-232E and V.28/V.24 communication interfaces, especially those that do not provide ±12V power.
The PL2303 is a highly integrated RS232-USB interface converter from Prolific that provides a convenient connection to an RS232 full-duplex asynchronous serial communication device with a USB function interface. The PL2303 has multiple historical versions. The earlier version was PL2303HX. In recent years, PL2303HXA, PL2303HXC, PL2303HXD (Version-D), and PL2303SA have been released, and the application circuits are different. Version-D does not require an external crystal and adds support for Android.
Difference between MAX232 and PL2303, CH340
Principle: The TXD and RXD of the MCU are TTL level, so you have to change the other signals into TTL levels. Only then can the MCU download program be successful! Among them, CH340, PL2303 and other chips directly convert USB signals to TTL level or TTL level to USB signals, while MAX232 and other chips convert TTL to RS232 signals or convert RS232 signals to TTL.
MAX232: Peripheral circuit is simple, but takes up a large area of PCB
PL2303: Parallel is unstable, the peripheral circuit is complicated, and the cost is low.
CH340: stable, simple peripheral circuit, relatively high cost
Method of communication between the computer and the MCU:
1. Desktop with serial port only (very old) Crossed serial cable 》MAX232 chip 》MCU (micro-controller)
2. Computer with serial port interface and USB interface (desktop)
(1) computer serial port interface 》cross serial cable 》MAX232 chip 》MCU (micro-controller)
(2) Computer USB interface 》USB to serial cable 》MAX232 chip 》MCU (micro-controller)
(3) Computer USB interface 》USB2.0 data cable 》PL2303 or CH340 》MCU (micro-controller)
3. Computer with only USB interface (notebook)
(1) Computer USB interface 》USB to serial cable 》MAX232 chip 》MCU (micro-controller)
(2) Computer USB interface 》USB2.0 data cable 》PL2303 or CH340> MCU (micro-controller)
Principle of computer and MCU communication:
(1) Cross-serial line principle: signal line crossing, wire function
(2) USB to serial line principle: USB interface PL2303 or CH340 MAX232 9-pin interface
(3) USB2.0 data line principle: signal line direct connection, wire function
Signal analysis:
Computer serial port interface computer output 232 level signal AX232 chip TTL level
Computer USB interface computer output USB level signal USB to serial line 232 level signal MAX232 chip TTL level
Computer USB interface computer output USB level signal PL2303 or CH340 chip TTL level