STC12LE5616AD datasheet(76/377 Pages) STC

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4.3 I/O port application notes

Traditional 8051 access I/O (signal transition or read status) timing is 12 clocks, STC12C5620AD series MCU is

4 clocks. When you need to read an external signal, if internal output a rising edge signal, for the traditional 8051,

this process is 12 clocks, you can read at once, but for STC12C5620AD series MCU, this process is 4 clocks,

when internal instructions is complete but external signal is not ready, so you must delay 1~2 nop operation.

When MCU is connected to a SPI or I2C or other open-drain peripherals circuit, you need add a 10K pull-up

resistor.

Some IO port connected to a PNP transistor, but no pul-up resistor. The correct access method is IO port pull-up

resistor and transistor base resistor should be consistent, or IO port is set to a strongly push-pull output mode.

Using IO port drive LED directly or matrix key scan, needs add a 470ohm to 1Kohm resistor to limit current.

4.4 Typical transistor control circuit

If I/O is configed as “weak” pull-up, you should add a external pull-up resistor R1(3.3K~10K ohm). If no pull-up

resistor R1, proposal to add a 15K ohm series resistor R2 at least or config I/O as “push-pull” mode.

common I/O port

10K(3.3K~10K)

15K(3.3K~15K)

4.5 Typical diode control circuit

I/O

For weak pull-up / quasi-bidirectional I/O, use sink current drive LED, current limiting resistor as greater than 1K

ohm, minimum not less than 470 ohm.

I/O

For push-pull / strong pull-up I/O, use drive current drive LED.

Vcc

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