All VSS and VDD pins must be connected. Even if one of these pins is not connected, programming may fail.
PIC16F916 can only be programmed with HVP (High Voltage Programming). This means it requires Vpp voltage (higher than Vdd) for programming. NSDSP cannot generate such voltages. Therefore, PIC16F916 requires NSHVX High Voltage Extension or an external HVP circuit.
Target Voltage Below 4.5V
If voltage is less than 4.5V programming is severely limited - it is impossible to bulk erase the device, it is also impossible to erase configuration bits, EEPROM, UID.
NSDSP cannot detect target voltage and it assumes that the voltage is above 4.5V. If the actual target voltage is less, programming will fail. However, if you tell NSDSP that the target voltage is below 4.5V through programming software, NSDSP will use special low-voltage programming mode. In this mode, NSDSP verifies if the desired programming can be performed at voltages below 4.5V, and if it is possible (device is not code protected, configuration bits do not change or only change from 1 to 0, EEPROM is not programmed, UID is not programmed), it performs the programming. If such programming is impossible, NSDSP software will stop and show an error message.
Programming in low-voltage mode may be considerably slower. In addition, you may need to decrease programming speed to 3MHz or below.
NSDSP cannot be used to debug PIC16F916.
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