[SOLVED] power on or reset problem with my 89s52 controller

[vinnu1]

Hi...,
i am designing a 89s52 based project.
in that controller port 2 is completely dedicated for outputs.
initially the port is off condition.
when i power on the controller or when i pressed reset button, the port is behaving as One sec on and then it will become off.
i don't know why it is behaving like this.,
please help me....

 

[arun_190175]

according datasheet on rest all ports are goes high while reset pin is high for one mcu cycle
according to your post port2 goes hi and low ,and also check reset network 10uf-10kohm

 

[milan.rajik]

I think on reset or power on reset the Port pins of 8051 remains high. Only after writing 0x00 to Ports it becomes low. Maybe you are doing like this in code.

---

Code C - [expand]
1
2
3
4
P0 = 0x00;
P1 = 0x00;
P2 = 0x00;
P3 = 0x00;

---

When MCU starts or is reset then Ports will be in high state and then PORTS become low.

 

[andre_luis]

You certainly defined the IDLE state for those ports differently from that specified on "Power On Reset" uC port registers. You can turn around either by decreasing the duration of reset state ( reducing the time base of its reset RC network ), or change the IDLE state of ports by inverting its logic 0/1, however this implies on a need to change all external port circuitry, inverting its logic accordingly.

 

[vinnu1]

Thank you so much...