This article mainly introduced the field busthe MODBUS correspondence protocol and some method of the VB apply in the serial communication-This article mainly introduced the field b usthe MODBUS protocol and some correspondence method of the VB apply

MDB 到RS232（串口）的应用电路图，其中BCX17 PNP管可以使用 9012代替。-MDB to RS232 (serial port) of the application circuit, which BCX17 PNP can use 9012 instead of tubes.