Interface circuit design of SPCE061A microcontroller and fingerprint identification module

 The SPCE061A microcontroller communicates with the fingerprint identification module OM-20 through the serial port. There is a standard full-duplex universal asynchronous receiver/transmitter UART inside the SPCE061A microcontroller. The UART's receiving signal Rx and sending signal Tx are shared with IOB7 and IOB10 respectively, which are special functions of port B. Since the serial port of the SPCE061A microcontroller uses TTL level, and the serial port of the fingerprint identification module OM-20 uses RS232 level, level conversion must be performed in order to achieve communication between the two. The RS232 standard is a serial bus standard officially announced by the Federation of Electronic Industries. The RS232 serial interface bus is suitable for communication distances between devices not greater than 15m, with a maximum transmission rate of 20kBps. RS232 uses negative logic to specify logic levels.

Discrete components or integrated circuit chips can be used to achieve RS232 and TTL logic level conversion. At present, the more widely used integrated circuit conversion devices, such as MC1488 and SN75150 chips, can complete the conversion from TTL level to RS232 level, while MC1489 and SN75154 can realize the conversion from RS232 level to TTL level. Figure 3.1 shows the interface circuit between the SPCE061A microcontroller and the fingerprint identification module OM-20. MAX232 is very sensitive to power supply noise, so a 1μf decoupling capacitor is added to Vcc. The capacitors C1, C2, C3 and C4 take 1μf decoupling capacitors to improve anti-interference. ability.