the 13a has the same footprint as a tiny85. specs are different. less ram, eeprom or flash. it should be doable, but after finding the tiny85 more worthwile i abandoned the 13a. i choose the tiny because of its physical size. the soic-8 is just 7.7 x 5.5 x 1.5 mm and with a internal rc clock you only need one external resistor to make it run.