Usb Pic Programmer Schematic Software Is Set
The hardware is built around a microchip PIC18F2550, this microcontroller has on board USB capabilities. If the Vcc setting on the programmer/software is set higher than is possible after USB voltage drops, diode drop and FET I*R drop, the device's Vcc will vary during programming and there is a good chance that it will fail.Since almost all modern PICs will program just fine at well below 5 volts, setting Vcc below the dropout threshold fixes this problem and I have had zero problems with it: I just have to remember to make sure that it is set there since the programming software doesn't always "remember" this parameter.For programming I use the standalone PicKit programming software from Microchip rather than that built into MPLAB - and it seems to handle the "MCLR" problem just fine (which was never a problem with the Picstart!) whereas this can sometimes be a fight on some devices with MPLAB. Programmer is used just first time for loading the code in microcontroller and after that we can directly load the code in microcontroller through this simpler circuit. PIC18F2550 and PIC18F4550 are famous for their USB Module.When replacing it I settled on the PicKit 3 (which is much faster in all ways!) but quickly found that it had problems - UNLESS I set the target supply voltage down from the default 5 volts to something like 4.0-4.5 volts, whereupon all of the problems with unreliable programming suddenly went away!This is also an EEPROM programmer as it supports 12Cxx EEPROM. USB PIC Programmer - Electronics-Lab.
It charges and discharges the capacitors C8 – C10 by toggling the signals on Pump1 and Pump2 Programming header P1The programming header is used to program a target board using ICSP (in circuit serial programming). Voltage pumpOn top of the schematic you see the voltage pump which converts the 5V of VDD to 12V on VPP. The controller connects to the PC by USB. The firmware is described on the Embedded page. Components MicrocontrollerA PIC18f2550 has been used to convert the USB commands to logical levels on the programming header. The hardware (from version 0.3) is capable of creating levels for PIC24 / PIC33 / PIC18FXXJXX devices as well.
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