Greetings KumaraGuruparan,You might benefit from putting pull-down resistors on those 8051 IO lines that are giving you problems.
On power-up, all of the digital IO lines come up in tristate mode so a pull-down will make sure that IO lines don't float to an undesired state.
I m using 8051 microcontroller. If i make the relay activation signal low what will happen when i switch off the the board.At that time all the port pins will go high.. The only solution on an 8051 is to make the relay activation signal active low with an inverter stage.
That really depends on the relationship between th micro controller power supply and the relay power supply. Also it depends on the type of relay and weather you are using normally open or normally closed contacts.I m using 8051 microcontroller. If i make the relay activation signal low what will happen when i switch off the the board.At that time all the port pins will go high.
I feel, you need to appreciate the basics of it. 8051 ports goes to high state during power cycle. So you get momentary switching on relay or any devices. If its connected to valve or motor, you definitely get irritated or complains from your customer. This is applicable in case of NO or NC contact.Kumara, tray to put all outs at low with the very first instruction in your code.
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by Jake Hertz