I picked up a new Mini from the recent Sparkfun $10 off $20+ sale. My old Mini is mounted on on a Parallax BOE which has the DB9 connector. I wanted to breadboard the new Mini, but breadboarding with a DB9 connecctor is unpleasant to say the least. The Picaxe line of chips use a RS232 programming interface, but it is possible to use a regular USB to serial adapter if TX/RX are inverted. TX from USB/serial is input to the inverter and the output from the inverter is input to RX; and conversely for RX. I decided to try this with the Mini using a 74LVC2G14 Schmitt trigger inverter and it worked. Probably any USB to serial adapter will work, but I used a Prolific PL-2302 at 9600 baud. I was able flash the new 4.2 firmware on the Mini RS232 connection with straight hardware inversion. No problems with SAM-BA, MFdeploy performed its job and happily pings, gives device capabilities and connects.
All of this worked transparently without the USB to RS232 adapter/DB9 connector. The 74LVC2G14 is a SOT23-6 2 gate part and perfect for this application. You can also use a 74HC14 in a dip or SOIC 14-lead arrangement.
The connections are:
USB/serial 74LVC2G14(In) 74LVC2G14(Out) MiniTX --> 1A (pin 1) 1Y (pin 6) --> RX (pin 2) USB/serial 74LVC2G14(Out) 74LVC2G14(In) MiniRX <-- 2Y (pin 4) 2A (pin 3) <-- TX (pin 1) DTR (pin 3, no connection)
Pin 2 of the inverter IC is ground and pin 5 is VCC (5V from the USB serial). I think it is important to use 5V and not 3.3V. Given that hardware inversion works, it can be completely eliminated by doing the inversion in firmware. The FTDI EEPROM programming utility has provision for inversion; download it here:
To use it (assuming you have a FTDI USB/serial adapter), under the menu devices click scan and parse. Invert RS232 is under Hardware specific in the tree. I did a Google search on the Forum for this type of Mini interface, but did not find anything so due apologies if this is a re-post on this topic.