STC12LE5616AD datasheet(77/377 Pages) STC

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4.6 3V/5V hybrid system

When STC12C5620AD series 5V MCU connect to 3.3V peripherals. To prevent the 3.3V device can not afford to

5V voltage, the 5V MCU corresponding I/O should first add a 330 ohm current limiting resistor to 3.3 device I/O

ports. And in intialization of procedures the 5V MCU corresponding I/O is set to open drain mode, disconnect the

internal pull-up resistor, the corresponding 3.3V device I/O port add 10K ohm external pull-up resistor to the 3.3V

device VCC, so high level to 3.3V and low to 0V, which can proper functioning

MCU common I/O

external input signal

When STC12LE5620AD series 3V MCU connect to 5V peripherals. To prevent the 3V MCU can not afford to 5V

voltage, if the corresponding I/O port as input port, the port may be in an isolation diode in series, isolated high-

voltage part. When the external signal is higher than MCU operating voltage, the diode cut-off, I/O have been

pulled high by the internal pull-up resistor; when the external signal is low, the diode conduction, I/O port voltage

is limited to 0.7V, it’s low signal to MCU.

5V MCU I/O port

10K

330Ω

3.3V device I/O port

3.3V

When STC12LE5620AD series 3V MCU connect to 5V peripherals. To prevent the 3V MCU can not afford to

5V voltage, if the corresponding I/O port as output port, the port may be connect a NPN transistor to isolate high-

voltage part. The circuit is shown as below.

common I/O port

10K

5V device I/O port

STC12LE5616AD Datasheet(PDF) 77 Page - STCmicro Technology Co,.Ltd