I can easily upload code to an Attiny 45 using the Arduino as ISP option. My Arduino Uno is wired to the Mosi, Miso and Sck pins of the Attiny (I believe this is the SPI bus).
I have just received one of these devices Rx63 Overview which has an Atmega 328, a 2.4GHz transceiver and a Hbridge. Because it is a very small device it doesn't have a connection to the Tx pin of the USART and so cannot be programmed using the bootloader. (I can upload the bootloader to the bigger Rx61 devices).
Am I right to think that I can upload a sketch to a 328 in the same way as to the Attiny?