microcode store (was Re: Looking to get into a Mini Computer...)#

Weel, sort-of. There is an 8 byte buffer which can be automaticlaly laoed with a quadword of memeory And there s a way to use the byecode as part of the addess for a microcode jump (basically a 256-wway fork). But there is nothing in the hardware that assume a particualr bytecode. No hardwired bits of decode logic. Obviosuly a 65536 (16 bit) fork would be impossible o na machien with only 4K or 16K fo control store. But there is, AFAIk, nothing to stop a microprogramemr writign code to extract fields from a 16 bit machien instrucion and feed therm int othe fork logic. So implementing a 16 bit instrucion set would not be hard or inefficient. THere is a rumour that there was a PDP11-compatible microcode at 3RCC. I know nothing about it, and AFAIK it doens't still exist :-( -tony