1. Both ISP and JTAG interfaces are extracted and labeled; 2. AD conversion reference voltage is added with filter inductor and capacitor; 3. Two frequency external crystal oscillators can be selected by jumpers; 4. All IO ports are drawn and marked; 5. Reliable reset circuit; 6. Lead up to four LEDs for simple testing; 7.miniUSB or pin power supply; 8. Double-sided copper coating to improve the stability of the board; 9.PCB specification: 49×69 (mm)