The pinout of the M0x is deliberately adjusted to the "biblical" '51 pinout. Look at it: if you cut 4 pins, each in one corner (those belonging to port P4), you'll get the same pinout as the usual QFP44 '51s come in quote for some time, and which is identical to the "biblical" DIP40 pinout rotated by a couple of pins. And we are talking about position of power pins (with some adjustments here and there), xtal pins, dedicated peripherals such as UART and SPI and I2C, and also the structure of general purpose ports! That's quite a difference from the "general" ARM offerings.

You might object that the package size etc. is different so one has to draw a new PCB anyway. Sure; but it's surely simpler when one has only to "shrink" the footprint of a single component, rather than to redesign everything. Also it appears to be simple to design a DIP40 adapter, when it comes to it. Also, Nuvoton offers most of their 12/6-clockers and some of the 4-clockers in a compatible LQFP48 package, and I would not be surprised if there would be other '51s in this package available.

The downside of this all is, that so far I was unable to buy a single Winbond/Nuvoton chip, and I've been trying for quite some time to get some of their LPCs and before that the RD2-equivalent (but the truth is that I was offered samples if I write a dummy project proposal, except I refused to do that as it would not be fair IMO). I also don't know how I would program them.

JW