Specific of programming PICmicro

1.Most of the PIC microcontrollers produced by Microchip Technology Corporation require a special HV ISP Programming Mode (High-Voltage in-System Programming Mode). In this mode a relatively high voltage of 13V is applied to the MCLR device pin. The user's equipment to be programmed should be designed in the way tolerating a 13V signal to be applied to the MCLR device pin - in particular this pin should not be connected to the Vcc pin of the device.

2.Though the PIC microcontrollers are capable to work in a certain range on the Vcc voltage (the range varies from 2 to 5V for some PICmicro derivatives) the device being under programming must have the 5V voltage level applied to the Vcc device pin. If in the working mode the target microcontroller works under the Vcc lower than 5V and the target cannot tolerate applying the 5V voltage to the Vcc pin, then, if the user needs to program the PICmicro device in-system, it is necessary to change the schematic to have an ability to connect 5V to the Vcc pin while the target is under the programming. However, verification of the correct programming can be conducted under the voltages allowed by the manufacturer (Vcc min - Vcc max).