SparkFun Forums 

Where electronics enthusiasts find answers.

Your source for all things Atmel.
By amsung2
forgive me for asking an out dated 8051 question in a high tech AVR forum. but i can't get sleep over this issue....
i programmed the 89c51 using the flash programmer; it took a few seconds. i connected the crystal oscillator etc. and then proceeded to connect the LEDs on port 2. when i connected the vcc to the microcontroller, i expected the LEDs to glow. but nothing is happening, is there a procedure to turn the microcontroller 'on'?
also, how many times can an89c51 be programed and erased? how long does it take to program it using a flash programmer?
i am new to programming microcontrollers, so excuse me for asking this silly question,
i can assure you, there aint any wiring errors. the MCU seems to be fine, i verified it. no question of a programming error, it is a pretty simple program to begin with.
what i want to know is, when is the execution supposed to start?
a)when the vcc is connected
b)when the reset pin is held low
c)any thing else?(i've tried the above 2)
but any sort of help will be greatly appreciated
also, can a microcontroller based circuit be powerd by one or two 9v batteries thru 7805?
By riden
The reset for a 89C51 is logic HIGH not low. In my older Atmel projects, I had a small capacitor between VCC and the RST pin and a 10k pulldown resistor to ground. That configuration would reset the chip on powerup. I Googled "89C51" and found a link that you may find helpful: ... TMEL-89C51
By newbie123
Did you forget to connect the EA (pin 31) on the microcontroller to VCC?
I'll bet that is the problem. IF left floating, the 89C51 will try to execute code from external memory.

Since we can't post files on this forum, I posted a circuit for you here:

the above circuit shows all the necessary connections needed for reset and EA.

Let us know if that was the problem.

Good Luck