This programmer is based on Thomas Fischl’s USBasp design and connects to your computer’s USB port. Not only is it quite compact, but the design is really elegant The USB interface is achieved by using an atmega processor and the rest is done in firmware. For those interested, the firmware source code can be downloaded from the USBasp website.
USB interface can be provided for the 5V power supply to Download and target board, in case of short circuit, computer motherboard dangerous. USB-powered port, 500 mA resettable fuse to prevent damage to the computer USB port (USB port overcurrent protection, but more than a protection more secure). When the output current greater than 500 mA (overcurrent or short-circuit), the self-recovery fuse will immediately cut off the current, the protection of computer motherboards! Resettable fuse will automatically return to normal state when the lifting of the short-circuit, the programmer can continue normal use!
Not simplify the design of the hardware circuit out any impact on the stability of the devices, The 3.6V zener especially firmly province, to ensure that the level of matching. PCB in accordance with the standards of high-speed board design, first-class stability. 10-pin isp socket mount one on the board, while saving space and beautiful, the most critical with multiple plug loose.
USBASP and parallel port download cable, its internal firmware. Many versions of the firmware, good or bad is different, the public version of the firmware governor jumper two tranches governor, inconvenient and speed rating; carefully selected and modify the firmware, multi-level automatic speed control.
Example: AVR microcontroller factory 1MHz internal oscillation circuit, when a lower speed automatic firmware download its download about 4K program required about three seconds; For the same model using an external 12MHz crystal oscillator of the microcontroller, the clock speed up can support higher download speeds, download the same program, the firmware automatically accelerate download only to be less than one second. Above experiment reflects the automatic speed control, customers can authenticate themselves!