The problem is that you connect 89C51RD2 to the computer serial port. 89C51 RD2 has bootloader so you don't need programmer device, you connect the 89C51RD2 directly to computer and send the hex file to the 89C51RD2. This is actually interesting choice of microcontroller. Whoever designed that circuit found the crystal they liked, read the crystal datasheet, saw that the crystal needs 22 pF capacitors and put those capacitors into the schematic. The crystal that you buy will have specification in its datasheet of what value capacitors to use. 89C51RD2 is not exactly old, but it has been on the market for the last 10? 15 years?, when it was developed the normal procedure was to use external crystals.įirst question now. However, older and today cheaper microcontrollers still use external crystals. In the past 5 years manufacturers started making controllers that don't need external crystals. NOT EVERY controller needs external crystal.
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