USB to 25-pin parallel “file transfer cable.” I saw someone tossing this out, and through the transparent shell, I could see too many components for a simple USB bridge chip. Conveniently, the IO is broken out for you, power supplied though USB and, it has a USB interface for your new age convenience. Because the software is stored in an external EEPROM, it’s simple to invoke the built in development bootloader — ground the SCL pin (I added a switch) to bypass the external software. Now, if you want to read or reprogram the EEPROM, just flip the switch back.