Can I program a factory fresh ATMega328P using the UART pins without burning a bootloader? These pins are TX, RX, VCC, GND, and DTR pins in the schematic below. They are not the ISP/SPI pins 10-13.
For example, if you program an Arduino Pro Mini (which requires an ICSP programmer) with a programmer, you're not connected to the ISP pins (basically the SPI interface: MOSI, MISO, SCLK, SS), but rather to the serial i/o and reset pins.
My understanding is that a bootloader is required if you want to program through these pins, because the Arduino bootloader looks for UART traffic at these pins upon startup and hands off operation to the user's code if no attempt at programming happens during this time.
That said, I also understand burning a bootloader is done through the ISP/SPI pins, and my PCB is already manufactured, which makes burning a boatloader somewhat of a hassle. So...
Can I program an ATMega328P through the UART pins fresh off the reel, or will I need rig up a way to burn a bootloader through the ISP pins first?