為解決當前計算機串行通訊接口只有USB，難以滿足舊型號設備或某些單片機要求RS232通訊的問題，設計出兩款RS232/USB電路。采用CH341A與MAX223集成電路芯片構建標準9線RS232/USB通用接口轉換器，無需編程。采用CH341A與PIC16F877A構建單片機與計算機之間的USB通訊電路，軟件遵循RS232通訊協議，硬件進行電平轉換。實際使用表明，這兩款產品與計算機端Windows 操作系統下的串口應用程序完全兼容，且通訊過程中無握手失敗現象。
Abstract: To solve the problem that current computer serial communication only with USB interface can not satisfy with the old type equipments or MCU to communicate with RS232， two kinds of RS232/USB circuit were designed.CH341A and MAX223 integrated circuit chips were used to create a standard 9-line RS232/USB universal interface convertor without programme. CH341A and PIC16F877A chips were adopted to build the USB communication circuit between computers and MCU. The software follows RS232 communication protocol， and the hardware converts electrical levels. Actual practices indicate that the two manufactures are compatible with serial application program of Windows operation system completely，and get avoid of handshake lost.
The LM35 of National Semiconductors that is used in this project is a precision centigrade temperature sensor, which has an analog output voltage. It has a range of -55潞C to +150潞C and a accuracy of 鹵0.5潞C . The output voltage is 10mV/潞C . The output voltage is converted by the AD convertor of the AT Mega8. The temperature is displayed on an LCD module. In this example the thermometer has a range of 0潞C to 40潞C and a resolution of 0.5潞C. If you want to have a readout in Fahrenheit you can use the LM34.
