https://groups.google.com/forum/#!topic/comp.sys.m6809/nhhvKV3YRD4

you need the "b" (faster clock speed) and the "e" (enhanced instruction set.) The "p" only means a plastic body. so you definitely need a 68b09e (or 68b09ep). They are not that easy to find any more.

The suffix E is for external or internal phase clock generator. Like the MC6800 has the needs two phase generator and the 6802 generates this itself (just needs a crystal).

Letters in the middle 68X00 indicate speed rating. I think there is only 68B09 and 6809

The final P is for plastic package. I don't think it ever came in anything but plastic

Prefix is a manufacturer designation. In this case, means STMicro manufactured the chip.

That is a correct part number for WMS computers like the sys 11 sound board.

Andrew mentioned most already.
MC = Motorola, EF = SGS Thomson, HD = Hitachi....all 6809 manufacturers.
6809 = 1MHz, 68A09 = 1.5MHz, 68B09 = 2Mhz
E version needs an External oscillator, non E has an internal oscillator.
P means Plastic housing, C means Ceramic with enhanced temperature range (i've seen many Hitachi HD6809 with ceramic housing).

Marco