I think I need to rephrase my question so it doesn't look like I haven't done any research...
I'm new to the 912 series chips. I have a couple of old 912DG128A boards that have a 6 pin port with the bdm pins (gnd, vcc, bkgd, reset, modb, moda) but I can't figure out what I can program them with. I read about the bdm interface in the device datasheet. I've done a lot of googling about bdms and from what I can tell the main open source ones were the OSBDM and the TBDML, but they've now been combined into the USBDM. If I understand correctly, the JS16 version is the current design. Under the JS16 section on usbdm at sourceforge, the HCS12 is listed as supported but the HC12 is not.
I also installed the flash programmer code from usbdm (written by pgo i think?) and ran it in windows but the 912DG128A is not in the device list.
It seems like the USBDM only works with the S (HCS12) chips and I don't understand why. I've emailed various makers of bdms found on ebay (which i think are clones of the USBDM) and they've said their units cannot program the 912DG128A. I found Daniel Malik's old TBDML debugging post and it looks like the old bdm could program this device, but I haven't been able to find any of them.
The 912DG128A is an old part, but it has an internal charge pump for flash and eeprom so Vpp of 12v isn't necessary. I read a post describing the 912 and 912S differences as a die size/technology change. I read the dev support chapter in the datasheet, regarding how to use the bkgd pin to start bdm mode, and then send flash commands to the chip... is the bdm spec for the 912DG128A somehow different from the S versions of the chip? Why can't the USBDM write the flash on this chip?
Any thoughts would be much appreciated.